arm64: expose FAR_EL1 tag bits in siginfo

Most architectures with the exception of alpha, mips, parisc and sparc use the same values for these flags. Move their definitions into asm-generic/signal-defs.h and allow the architectures with non-standard values to override them. Also, document the non-standard flag values in order to make it easier to add new generic flags in the future.

A consequence of this change is that on powerpc and x86, the constants' values aside from SA_RESETHAND change signedness from unsigned to signed. This is not expected to impact realistic use of these constants. In particular the typical use of the constants where they are or'ed together and assigned to sa_flags (or another int variable) would not be affected.

Signed-off-by Peter Collingbourne <[email protected]>

Acked-by Geert Uytterhoeven <[email protected]>

Link https://linux-review.googlesource.com/id/Ia3849f18b8009bf41faca374e701cdca36974528

---
v11:
- tweak the commit message to point out the change from unsigned to signed

v10:
- move the comments around and add one for SA_SIGINFO

 arch/alpha/include/uapi/asm/signal.h   | 14 --------
 arch/arm/include/uapi/asm/signal.h     | 28 ++-------------
 arch/h8300/include/uapi/asm/signal.h   | 24 -------------
 arch/ia64/include/uapi/asm/signal.h    | 24 -------------
 arch/m68k/include/uapi/asm/signal.h    | 24 -------------
 arch/mips/include/uapi/asm/signal.h    | 12 -------
 arch/parisc/include/uapi/asm/signal.h  | 13 -------
 arch/powerpc/include/uapi/asm/signal.h | 24 -------------
 arch/s390/include/uapi/asm/signal.h    | 24 -------------
 arch/sparc/include/uapi/asm/signal.h   |  4 +--
 arch/x86/include/uapi/asm/signal.h     | 24 -------------
 arch/xtensa/include/uapi/asm/signal.h  | 24 -------------
 include/uapi/asm-generic/signal-defs.h | 47 ++++++++++++++++++++++++++
 include/uapi/asm-generic/signal.h      | 29 ----------------
 14 files changed, 51 insertions(+), 264 deletions(-)

arch/alpha/include/uapi/asm/signal.h +0 -14

index 74c750bf1c1a..a69dd8d080a8 100644
@@ -60,20 +60,6 @@ typedef unsigned long sigset_t;
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-
 #define SA_ONSTACK	0x00000001
 #define SA_RESTART	0x00000002
 #define SA_NOCLDSTOP	0x00000004

arch/arm/include/uapi/asm/signal.h +3 -25

index 9b4185ba4f8a..7727f0984d26 100644
@@ -60,33 +60,11 @@ typedef unsigned long sigset_t;
 #define SIGSWI		32
 
 /*
- * SA_FLAGS values:
- *
- * SA_NOCLDSTOP		flag to turn off SIGCHLD when children stop.
- * SA_NOCLDWAIT		flag on SIGCHLD to inhibit zombies.
- * SA_SIGINFO		deliver the signal with SIGINFO structs
- * SA_THIRTYTWO		delivers the signal in 32-bit mode, even if the task 
- *			is running in 26-bit.
- * SA_ONSTACK		allows alternate signal stacks (see sigaltstack(2)).
- * SA_RESTART		flag to get restarting signals (which were the default long ago)
- * SA_NODEFER		prevents the current signal from being masked in the handler.
- * SA_RESETHAND		clears the handler when the signal is delivered.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
+ * SA_THIRTYTWO historically meant deliver the signal in 32-bit mode, even if
+ * the task is running in 26-bit. But since the kernel no longer supports
+ * 26-bit mode, the flag has no effect.
  */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002
-#define SA_SIGINFO	0x00000004
 #define SA_THIRTYTWO	0x02000000
-#define SA_RESTORER	0x04000000
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
 
 #define MINSIGSTKSZ	2048
 #define SIGSTKSZ	8192

arch/h8300/include/uapi/asm/signal.h +0 -24

index e15521037348..2cd0dce2b6a6 100644
@@ -57,30 +57,6 @@ typedef unsigned long sigset_t;
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002 /* not supported yet */
-#define SA_SIGINFO	0x00000004
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define SA_RESTORER	0x04000000
 
 #define MINSIGSTKSZ	2048

arch/ia64/include/uapi/asm/signal.h +0 -24

index aa98ff1b9e22..38166a88e4c9 100644
@@ -53,30 +53,6 @@
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002
-#define SA_SIGINFO	0x00000004
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define SA_RESTORER	0x04000000
 
 /*

arch/m68k/include/uapi/asm/signal.h +0 -24

index 915cc755a184..4619291df601 100644
@@ -57,30 +57,6 @@ typedef unsigned long sigset_t;
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002
-#define SA_SIGINFO	0x00000004
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define MINSIGSTKSZ	2048
 #define SIGSTKSZ	8192
 

arch/mips/include/uapi/asm/signal.h +0 -12

index 53104b10aae2..e6c78a15cb2f 100644
@@ -62,18 +62,6 @@ typedef unsigned long old_sigset_t;		/* at least 32 bits */
 #define SIGRTMAX	_NSIG
 
 /*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- *
  * SA_RESTORER used to be defined as 0x04000000 but only the O32 ABI ever
  * supported its use and no libc was using it, so the entire sa-restorer
  * functionality was removed with lmo commit 39bffc12c3580ab for 2.5.48

arch/parisc/include/uapi/asm/signal.h +0 -13

index 9e6f87bc8a73..e5a2657477ac 100644
@@ -41,19 +41,6 @@
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
 #define SA_ONSTACK	0x00000001
 #define SA_RESETHAND	0x00000004
 #define SA_NOCLDSTOP	0x00000008

arch/powerpc/include/uapi/asm/signal.h +0 -24

index 85b0a7aa43e7..04873dd311c2 100644
@@ -60,30 +60,6 @@ typedef struct {
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK is not currently supported, but will allow sigaltstack(2).
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001U
-#define SA_NOCLDWAIT	0x00000002U
-#define SA_SIGINFO	0x00000004U
-#define SA_ONSTACK	0x08000000U
-#define SA_RESTART	0x10000000U
-#define SA_NODEFER	0x40000000U
-#define SA_RESETHAND	0x80000000U
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define SA_RESTORER	0x04000000U
 
 #define MINSIGSTKSZ	2048

arch/s390/include/uapi/asm/signal.h +0 -24

index 9a14a611ed82..0189f326aac5 100644
@@ -65,30 +65,6 @@ typedef unsigned long sigset_t;
 #define SIGRTMIN        32
 #define SIGRTMAX        _NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP    0x00000001
-#define SA_NOCLDWAIT    0x00000002
-#define SA_SIGINFO      0x00000004
-#define SA_ONSTACK      0x08000000
-#define SA_RESTART      0x10000000
-#define SA_NODEFER      0x40000000
-#define SA_RESETHAND    0x80000000
-
-#define SA_NOMASK       SA_NODEFER
-#define SA_ONESHOT      SA_RESETHAND
-
 #define SA_RESTORER     0x04000000
 
 #define MINSIGSTKSZ     2048

arch/sparc/include/uapi/asm/signal.h +1 -3

index ff9505923b9a..53758d53ac0e 100644
@@ -137,13 +137,11 @@ struct sigstack {
 #define SA_STACK	_SV_SSTACK
 #define SA_ONSTACK	_SV_SSTACK
 #define SA_RESTART	_SV_INTR
-#define SA_ONESHOT	_SV_RESET
+#define SA_RESETHAND	_SV_RESET
 #define SA_NODEFER	0x20u
 #define SA_NOCLDWAIT    0x100u
 #define SA_SIGINFO      0x200u
 
-#define SA_NOMASK	SA_NODEFER
-
 #define SIG_BLOCK          0x01	/* for blocking signals */
 #define SIG_UNBLOCK        0x02	/* for unblocking signals */
 #define SIG_SETMASK        0x04	/* for setting the signal mask */

arch/x86/include/uapi/asm/signal.h +0 -24

index e5745d593dc7..164a22a72984 100644
@@ -62,30 +62,6 @@ typedef unsigned long sigset_t;
 #define SIGRTMIN	32
 #define SIGRTMAX	_NSIG
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001u
-#define SA_NOCLDWAIT	0x00000002u
-#define SA_SIGINFO	0x00000004u
-#define SA_ONSTACK	0x08000000u
-#define SA_RESTART	0x10000000u
-#define SA_NODEFER	0x40000000u
-#define SA_RESETHAND	0x80000000u
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define SA_RESTORER	0x04000000
 
 #define MINSIGSTKSZ	2048

arch/xtensa/include/uapi/asm/signal.h +0 -24

index 005dec5bfde4..79ddabaa4e5d 100644
@@ -72,30 +72,6 @@ typedef struct {
 #define SIGRTMIN	32
 #define SIGRTMAX	(_NSIG-1)
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002 /* not supported yet */
-#define SA_SIGINFO	0x00000004
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
 #define SA_RESTORER	0x04000000
 
 #define MINSIGSTKSZ	2048

include/uapi/asm-generic/signal-defs.h +47 -0

index e9304c95ceea..493953fe319b 100644
@@ -4,6 +4,53 @@
 
 #include <linux/compiler.h>
 
+/*
+ * SA_FLAGS values:
+ *
+ * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
+ * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
+ * SA_SIGINFO delivers the signal with SIGINFO structs.
+ * SA_ONSTACK indicates that a registered stack_t will be used.
+ * SA_RESTART flag to get restarting signals (which were the default long ago)
+ * SA_NODEFER prevents the current signal from being masked in the handler.
+ * SA_RESETHAND clears the handler when the signal is delivered.
+ *
+ * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
+ * Unix names RESETHAND and NODEFER respectively.
+ *
+ * The following bits are used in architecture-specific SA_* definitions and
+ * should be avoided for new generic flags: 3, 4, 5, 6, 7, 8, 9, 16, 24, 25, 26.
+ */
+#ifndef SA_NOCLDSTOP
+#define SA_NOCLDSTOP	0x00000001
+#endif
+#ifndef SA_NOCLDWAIT
+#define SA_NOCLDWAIT	0x00000002
+#endif
+#ifndef SA_SIGINFO
+#define SA_SIGINFO	0x00000004
+#endif
+#ifndef SA_ONSTACK
+#define SA_ONSTACK	0x08000000
+#endif
+#ifndef SA_RESTART
+#define SA_RESTART	0x10000000
+#endif
+#ifndef SA_NODEFER
+#define SA_NODEFER	0x40000000
+#endif
+#ifndef SA_RESETHAND
+#define SA_RESETHAND	0x80000000
+#endif
+
+#define SA_NOMASK	SA_NODEFER
+#define SA_ONESHOT	SA_RESETHAND
+
+/*
+ * New architectures should not define the obsolete
+ *	SA_RESTORER	0x04000000
+ */
+
 #ifndef SIG_BLOCK
 #define SIG_BLOCK          0	/* for blocking signals */
 #endif

include/uapi/asm-generic/signal.h +0 -29

index 5c716a952cbe..f634822906e4 100644
@@ -52,35 +52,6 @@
 #define SIGRTMAX	_NSIG
 #endif
 
-/*
- * SA_FLAGS values:
- *
- * SA_ONSTACK indicates that a registered stack_t will be used.
- * SA_RESTART flag to get restarting signals (which were the default long ago)
- * SA_NOCLDSTOP flag to turn off SIGCHLD when children stop.
- * SA_RESETHAND clears the handler when the signal is delivered.
- * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
- * SA_NODEFER prevents the current signal from being masked in the handler.
- *
- * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
- * Unix names RESETHAND and NODEFER respectively.
- */
-#define SA_NOCLDSTOP	0x00000001
-#define SA_NOCLDWAIT	0x00000002
-#define SA_SIGINFO	0x00000004
-#define SA_ONSTACK	0x08000000
-#define SA_RESTART	0x10000000
-#define SA_NODEFER	0x40000000
-#define SA_RESETHAND	0x80000000
-
-#define SA_NOMASK	SA_NODEFER
-#define SA_ONESHOT	SA_RESETHAND
-
-/*
- * New architectures should not define the obsolete
- *	SA_RESTORER	0x04000000
- */
-
 #if !defined MINSIGSTKSZ || !defined SIGSTKSZ
 #define MINSIGSTKSZ	2048
 #define SIGSTKSZ	8192

Signature · 7 lines

2.29.0.rc1.297.gfa9743e501-goog


_______________________________________________
linux-arm-kernel mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Previously we were not clearing non-uapi flag bits in sigaction.sa_flags when storing the userspace-provided sa_flags or when returning them via oldact. Start doing so.

This allows userspace to detect missing support for flag bits and allows the kernel to use non-uapi bits internally, as we are already doing in arch/x86 for two flag bits. Now that this change is in place, we no longer need the code in arch/x86 that was hiding these bits from userspace, so remove it.

This is technically a userspace-visible behavior change for sigaction, as the unknown bits returned via oldact.sa_flags are no longer set. However, we are free to define the behavior for unknown bits exactly because their behavior is currently undefined, so for now we can define the meaning of each of them to be "clear the bit in oldact.sa_flags unless the bit becomes known in the future". Furthermore, this behavior is consistent with OpenBSD [1], illumos [2] and XNU [3] (FreeBSD [4] and NetBSD [5] fail the syscall if unknown bits are set). So there is some precedent for this behavior in other kernels, and in particular in XNU, which is probably the most popular kernel among those that I looked at, which means that this change is less likely to be a compatibility issue.

Link [1] https://github.com/openbsd/src/blob/f634a6a4b5bf832e9c1de77f7894ae2625e74484/sys/kern/kern_sig.c#L278

Link [2] https://github.com/illumos/illumos-gate/blob/76f19f5fdc974fe5be5c82a556e43a4df93f1de1/usr/src/uts/common/syscall/sigaction.c#L86

Link [3] https://github.com/apple/darwin-xnu/blob/a449c6a3b8014d9406c2ddbdc81795da24aa7443/bsd/kern/kern_sig.c#L480

Link [4] https://github.com/freebsd/freebsd/blob/eded70c37057857c6e23fae51f86b8f8f43cd2d0/sys/kern/kern_sig.c#L699

Link [5] https://github.com/NetBSD/src/blob/3365779becdcedfca206091a645a0e8e22b2946e/sys/kern/sys_sig.c#L473

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/I35aab6f5be932505d90f3b3450c083b4db1eca86

---
v10:
- rename SA_UAPI_FLAGS -> UAPI_SA_FLAGS
- refactor how we define it to avoid mentioning flags more than once

 arch/arm/include/asm/signal.h    |  2 ++
 arch/parisc/include/asm/signal.h |  2 ++
 arch/x86/kernel/signal_compat.c  |  7 -------
 include/linux/signal_types.h     | 12 ++++++++++++
 kernel/signal.c                  | 10 ++++++++++
 5 files changed, 26 insertions(+), 7 deletions(-)

arch/arm/include/asm/signal.h +2 -0

index 65530a042009..430be7774402 100644
@@ -17,6 +17,8 @@ typedef struct {
 	unsigned long sig[_NSIG_WORDS];
 } sigset_t;
 
+#define __ARCH_UAPI_SA_FLAGS	(SA_THIRTYTWO | SA_RESTORER)
+
 #define __ARCH_HAS_SA_RESTORER
 
 #include <asm/sigcontext.h>

arch/parisc/include/asm/signal.h +2 -0

index 715c96ba2ec8..30dd1e43ef88 100644
@@ -21,6 +21,8 @@ typedef struct {
 	unsigned long sig[_NSIG_WORDS];
 } sigset_t;
 
+#define __ARCH_UAPI_SA_FLAGS	_SA_SIGGFAULT
+
 #include <asm/sigcontext.h>
 
 #endif /* !__ASSEMBLY */

arch/x86/kernel/signal_compat.c +0 -7

index a7f3e12cfbdb..ddfd919be46c 100644
@@ -165,16 +165,9 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
 {
 	signal_compat_build_tests();
 
-	/* Don't leak in-kernel non-uapi flags to user-space */
-	if (oact)
-		oact->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
-
 	if (!act)
 		return;
 
-	/* Don't let flags to be set from userspace */
-	act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
-
 	if (in_ia32_syscall())
 		act->sa.sa_flags |= SA_IA32_ABI;
 	if (in_x32_syscall())

include/linux/signal_types.h +12 -0

index f8a90ae9c6ec..a7887ad84d36 100644
@@ -68,4 +68,16 @@ struct ksignal {
 	int sig;
 };
 
+#ifndef __ARCH_UAPI_SA_FLAGS
+#ifdef SA_RESTORER
+#define __ARCH_UAPI_SA_FLAGS	SA_RESTORER
+#else
+#define __ARCH_UAPI_SA_FLAGS	0
+#endif
+#endif
+
+#define UAPI_SA_FLAGS                                                          \
+	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \
+	 SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS)
+
 #endif /* _LINUX_SIGNAL_TYPES_H */

kernel/signal.c +10 -0

index a38b3edc6851..2ef8c238679e 100644
@@ -3984,6 +3984,16 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 	if (oact)
 		*oact = *k;
 
+	/*
+	 * Clear unknown flag bits in order to allow userspace to detect missing
+	 * support for flag bits and to allow the kernel to use non-uapi bits
+	 * internally.
+	 */
+	if (act)
+		act->sa.sa_flags &= UAPI_SA_FLAGS;
+	if (oact)
+		oact->sa.sa_flags &= UAPI_SA_FLAGS;
+
 	sigaction_compat_abi(act, oact);
 
 	if (act) {

Signature · 7 lines

2.29.0.rc1.297.gfa9743e501-goog


_______________________________________________
linux-arm-kernel mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

This field will contain flags that may be used by signal handlers to determine whether other fields in the _sigfault portion of siginfo are valid. An example use case is the following patch, which introduces the si_addr_tag_bits{,_mask} fields.

A new sigcontext flag, SA_XFLAGS, is introduced in order to allow a signal handler to require the kernel to set the field (but note that the field will be set anyway if the kernel supports the flag, regardless of its value). In combination with the previous patches, this allows a userspace program to determine whether the kernel will set the field.

It is possible for an si_xflags-unaware program to cause a signal handler in an si_xflags-aware program to be called with a provided siginfo data structure by using one of the following syscalls:

- ptrace(PTRACE_SETSIGINFO)
- pidfd_send_signal
- rt_sigqueueinfo
- rt_tgsigqueueinfo

So we need to prevent the si_xflags-unaware program from causing an uninitialized read of si_xflags in the si_xflags-aware program when it uses one of these syscalls.

The last three cases can be handled by observing that each of these syscalls fails if si_code >= 0. We also observe that kill(2) and tgkill(2) may be used to send a signal where si_code == 0 (SI_USER), so we define si_xflags to only be valid if si_code > 0.

There is no such check on si_code in ptrace(PTRACE_SETSIGINFO), so we make ptrace(PTRACE_SETSIGINFO) clear the si_xflags field if it detects that the signal would use the _sigfault layout, and introduce a new ptrace request type, PTRACE_SETSIGINFO2, that a si_xflags-aware program may use to opt out of this behavior.

It is also possible for the kernel to inject a signal specified to use _sigfault by calling force_sig (e.g. there are numerous calls to force_sig(SIGSEGV)). In this case si_code is set to SI_KERNEL and the _kill union member is used, so document that si_code must be < SI_KERNEL.

Ideally this field could have just been named si_flags, but that name was already taken by ia64, so a different name was chosen.

I considered making ia64's si_flags a generic field and having it appear at the end of _sigfault (in the same place as this patch has si_xflags) on non-ia64, keeping it in the same place on ia64. ia64's si_flags is a 32-bit field with only one flag bit allocated, so we would have 31 bits to use if we do this. However, it seems simplest to avoid entangling these fields.

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/Ide155ce29366c3eab2a944ae4c51205982e5b8b2

---
v12:
- Change type of si_xflags to u32 to avoid increasing alignment
- Add si_xflags to signal_compat.c test cases

v11:
- update comment to say that si_code must > 0
- change ptrace(PTRACE_SETSIGINFO2) to take a flags argument

v10:
- make the new field compatible with the various ways that a siginfo can be injected from another process
- eliminate some duplication by adding a refactoring patch before this one

 arch/powerpc/platforms/powernv/vas-fault.c |  1 +
 arch/x86/kernel/signal_compat.c            |  7 +++--
 include/linux/compat.h                     |  2 ++
 include/linux/signal_types.h               |  2 +-
 include/uapi/asm-generic/siginfo.h         |  4 +++
 include/uapi/asm-generic/signal-defs.h     |  4 +++
 include/uapi/linux/ptrace.h                | 12 ++++++++
 kernel/ptrace.c                            | 32 ++++++++++++++++++----
 kernel/signal.c                            |  3 ++
 9 files changed, 58 insertions(+), 9 deletions(-)

arch/powerpc/platforms/powernv/vas-fault.c +1 -0

index 3d21fce254b7..3bbb335561f5 100644
@@ -154,6 +154,7 @@ static void update_csb(struct vas_window *window,
 	info.si_errno = EFAULT;
 	info.si_code = SEGV_MAPERR;
 	info.si_addr = csb_addr;
+	info.si_xflags = 0;
 
 	/*
 	 * process will be polling on csb.flags after request is sent to

arch/x86/kernel/signal_compat.c +5 -2

index ddfd919be46c..243a8cc3b41b 100644
@@ -121,8 +121,8 @@ static inline void signal_compat_build_tests(void)
 #endif
 
 	CHECK_CSI_OFFSET(_sigfault);
-	CHECK_CSI_SIZE  (_sigfault, 4*sizeof(int));
-	CHECK_SI_SIZE   (_sigfault, 8*sizeof(int));
+	CHECK_CSI_SIZE  (_sigfault, 8*sizeof(int));
+	CHECK_SI_SIZE   (_sigfault, 16*sizeof(int));
 
 	BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x10);
 	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr) != 0x0C);

@@ -138,6 +138,9 @@ static inline void signal_compat_build_tests(void)
 	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x20);
 	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pkey) != 0x14);
 
+	BUILD_BUG_ON(offsetof(siginfo_t, si_xflags) != 0x48);
+	BUILD_BUG_ON(offsetof(compat_siginfo_t, si_xflags) != 0x28);
+
 	CHECK_CSI_OFFSET(_sigpoll);
 	CHECK_CSI_SIZE  (_sigpoll, 2*sizeof(int));
 	CHECK_SI_SIZE   (_sigpoll, 4*sizeof(int));

include/linux/compat.h +2 -0

index 14d514233e1d..ea77a24ce6a2 100644
@@ -236,7 +236,9 @@ typedef struct compat_siginfo {
 					char _dummy_pkey[__COMPAT_ADDR_BND_PKEY_PAD];
 					u32 _pkey;
 				} _addr_pkey;
+				compat_uptr_t _pad[6];
 			};
+			u32 _xflags;
 		} _sigfault;
 
 		/* SIGPOLL */

include/linux/signal_types.h +1 -1

index a7887ad84d36..75ca861d982a 100644
@@ -78,6 +78,6 @@ struct ksignal {
 
 #define UAPI_SA_FLAGS                                                          \
 	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \
-	 SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS)
+	 SA_NODEFER | SA_RESETHAND | SA_XFLAGS | __ARCH_UAPI_SA_FLAGS)
 
 #endif /* _LINUX_SIGNAL_TYPES_H */

include/uapi/asm-generic/siginfo.h +4 -0

index 7aacf9389010..8158d5df666a 100644
@@ -91,7 +91,9 @@ union __sifields {
 				char _dummy_pkey[__ADDR_BND_PKEY_PAD];
 				__u32 _pkey;
 			} _addr_pkey;
+			void *_pad[6];
 		};
+		__u32 _xflags;
 	} _sigfault;
 
 	/* SIGPOLL */

@@ -152,6 +154,8 @@ typedef struct siginfo {
 #define si_trapno	_sifields._sigfault._trapno
 #endif
 #define si_addr_lsb	_sifields._sigfault._addr_lsb
+/* si_xflags is only valid if 0 < si_code < SI_KERNEL */
+#define si_xflags	_sifields._sigfault._xflags
 #define si_lower	_sifields._sigfault._addr_bnd._lower
 #define si_upper	_sifields._sigfault._addr_bnd._upper
 #define si_pkey		_sifields._sigfault._addr_pkey._pkey

include/uapi/asm-generic/signal-defs.h +4 -0

index 0126ebda4d31..cd522819f4ba 100644
@@ -20,6 +20,9 @@
  * so this bit allows flag bit support to be detected from userspace while
  * allowing an old kernel to be distinguished from a kernel that supports every
  * flag bit.
+ * SA_XFLAGS indicates that the signal handler requires the siginfo.si_xflags
+ * field to be valid. Note that if the kernel supports SA_XFLAGS, the field will
+ * be valid regardless of the value of this flag.
  *
  * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
  * Unix names RESETHAND and NODEFER respectively.

@@ -49,6 +52,7 @@
 #define SA_RESETHAND	0x80000000
 #endif
 #define SA_UNSUPPORTED	0x00000400
+#define SA_XFLAGS	0x00000800
 
 #define SA_NOMASK	SA_NODEFER
 #define SA_ONESHOT	SA_RESETHAND

include/uapi/linux/ptrace.h +12 -0

index a71b6e3b03eb..93946edf0139 100644
@@ -101,6 +101,18 @@ struct ptrace_syscall_info {
 	};
 };
 
+#define PTRACE_SETSIGINFO2	0x420f
+/*
+ * These flags are passed as the addr argument to ptrace.
+ */
+
+/*
+ * Asserts that the caller is aware of the field siginfo.si_xflags. Prevents
+ * the kernel from automatically setting the field to 0 when the signal uses
+ * a sigfault layout.
+ */
+#define PTRACE_SIGINFO_XFLAGS	0x1
+
 /*
  * These values are stored in task->ptrace_message
  * by tracehook_report_syscall_* to describe the current syscall-stop.

kernel/ptrace.c +18 -4

index 43d6179508d6..85b5b4e38661 100644
@@ -687,18 +687,32 @@ static int ptrace_getsiginfo(struct task_struct *child, kernel_siginfo_t *info)
 	return error;
 }
 
-static int ptrace_setsiginfo(struct task_struct *child, const kernel_siginfo_t *info)
+static int ptrace_setsiginfo(struct task_struct *child, unsigned long flags,
+			     kernel_siginfo_t *info)
 {
-	unsigned long flags;
+	unsigned long lock_flags;
 	int error = -ESRCH;
 
-	if (lock_task_sighand(child, &flags)) {
+	if (flags & ~PTRACE_SIGINFO_XFLAGS) {
+		return -EINVAL;
+	}
+
+	/*
+	 * If the caller is unaware of si_xflags and we're using a layout that
+	 * requires it, set it to 0 which means "no fields are available".
+	 */
+	if (!(flags & PTRACE_SIGINFO_XFLAGS) &&
+	    siginfo_layout_is_fault(
+		    siginfo_layout(info->si_signo, info->si_code)))
+		info->si_xflags = 0;
+
+	if (lock_task_sighand(child, &lock_flags)) {
 		error = -EINVAL;
 		if (likely(child->last_siginfo != NULL)) {
 			copy_siginfo(child->last_siginfo, info);
 			error = 0;
 		}
-		unlock_task_sighand(child, &flags);
+		unlock_task_sighand(child, &lock_flags);
 	}
 	return error;
 }

Quoted 11 lines · Peter Collingbourne

This field will contain flags that may be used by signal handlers to determine whether other fields in the _sigfault portion of siginfo are valid. An example use case is the following patch, which introduces the si_addr_tag_bits{,_mask} fields.

A new sigcontext flag, SA_XFLAGS, is introduced in order to allow a signal handler to require the kernel to set the field (but note that the field will be set anyway if the kernel supports the flag, regardless of its value). In combination with the previous patches, this allows a userspace program to determine whether the kernel will set the field.

Apologies for this coming rather late:

It occurs to me that we might want a more specific name, since this only applies to fault signals -- say, SA_FAULTFLAGS.

If we end up wanting to add flags fields for other signal types, then we might end up needing a SA_ flag for each, which would be a bit annoying.

So, alternatively. I wonder whether it's worth preemptively adding an extra flags to every kind of kernel-generated siginfo. If so, then having a single SA_XFLAGS would be fine.

If added flags fields all over the place is considered overkill, then I guess it's sufficient to rename this flag.

If renaming, the actual flags field in siginfo should also be renamed to match.

Quoted 241 lines

It is possible for an si_xflags-unaware program to cause a signal handler in an si_xflags-aware program to be called with a provided siginfo data structure by using one of the following syscalls:

- ptrace(PTRACE_SETSIGINFO)
- pidfd_send_signal
- rt_sigqueueinfo
- rt_tgsigqueueinfo

So we need to prevent the si_xflags-unaware program from causing an uninitialized read of si_xflags in the si_xflags-aware program when it uses one of these syscalls.

The last three cases can be handled by observing that each of these syscalls fails if si_code >= 0. We also observe that kill(2) and tgkill(2) may be used to send a signal where si_code == 0 (SI_USER), so we define si_xflags to only be valid if si_code > 0.

There is no such check on si_code in ptrace(PTRACE_SETSIGINFO), so we make ptrace(PTRACE_SETSIGINFO) clear the si_xflags field if it detects that the signal would use the _sigfault layout, and introduce a new ptrace request type, PTRACE_SETSIGINFO2, that a si_xflags-aware program may use to opt out of this behavior.

It is also possible for the kernel to inject a signal specified to use _sigfault by calling force_sig (e.g. there are numerous calls to force_sig(SIGSEGV)). In this case si_code is set to SI_KERNEL and the _kill union member is used, so document that si_code must be < SI_KERNEL.

Ideally this field could have just been named si_flags, but that name was already taken by ia64, so a different name was chosen.

I considered making ia64's si_flags a generic field and having it appear at the end of _sigfault (in the same place as this patch has si_xflags) on non-ia64, keeping it in the same place on ia64. ia64's si_flags is a 32-bit field with only one flag bit allocated, so we would have 31 bits to use if we do this. However, it seems simplest to avoid entangling these fields.

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/Ide155ce29366c3eab2a944ae4c51205982e5b8b2

---
v12:
- Change type of si_xflags to u32 to avoid increasing alignment
- Add si_xflags to signal_compat.c test cases

v11:
- update comment to say that si_code must > 0
- change ptrace(PTRACE_SETSIGINFO2) to take a flags argument

v10:
- make the new field compatible with the various ways that a siginfo can be injected from another process
- eliminate some duplication by adding a refactoring patch before this one

 arch/powerpc/platforms/powernv/vas-fault.c |  1 +
 arch/x86/kernel/signal_compat.c            |  7 +++--
 include/linux/compat.h                     |  2 ++
 include/linux/signal_types.h               |  2 +-
 include/uapi/asm-generic/siginfo.h         |  4 +++
 include/uapi/asm-generic/signal-defs.h     |  4 +++
 include/uapi/linux/ptrace.h                | 12 ++++++++
 kernel/ptrace.c                            | 32 ++++++++++++++++++----
 kernel/signal.c                            |  3 ++
 9 files changed, 58 insertions(+), 9 deletions(-)

arch/powerpc/platforms/powernv/vas-fault.c +1 -0

index 3d21fce254b7..3bbb335561f5 100644
@@ -154,6 +154,7 @@ static void update_csb(struct vas_window *window,
      info.si_errno = EFAULT;
      info.si_code = SEGV_MAPERR;
      info.si_addr = csb_addr;
+     info.si_xflags = 0;
 
      /*
       * process will be polling on csb.flags after request is sent to

arch/x86/kernel/signal_compat.c +5 -2

index ddfd919be46c..243a8cc3b41b 100644
@@ -121,8 +121,8 @@ static inline void signal_compat_build_tests(void)
 #endif
 
      CHECK_CSI_OFFSET(_sigfault);
-     CHECK_CSI_SIZE  (_sigfault, 4*sizeof(int));
-     CHECK_SI_SIZE   (_sigfault, 8*sizeof(int));
+     CHECK_CSI_SIZE  (_sigfault, 8*sizeof(int));
+     CHECK_SI_SIZE   (_sigfault, 16*sizeof(int));
 
      BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x10);
      BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr) != 0x0C);

@@ -138,6 +138,9 @@ static inline void signal_compat_build_tests(void)
      BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x20);
      BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pkey) != 0x14);
 
+     BUILD_BUG_ON(offsetof(siginfo_t, si_xflags) != 0x48);
+     BUILD_BUG_ON(offsetof(compat_siginfo_t, si_xflags) != 0x28);
+
      CHECK_CSI_OFFSET(_sigpoll);
      CHECK_CSI_SIZE  (_sigpoll, 2*sizeof(int));
      CHECK_SI_SIZE   (_sigpoll, 4*sizeof(int));

include/linux/compat.h +2 -0

index 14d514233e1d..ea77a24ce6a2 100644
@@ -236,7 +236,9 @@ typedef struct compat_siginfo {
                                      char _dummy_pkey[__COMPAT_ADDR_BND_PKEY_PAD];
                                      u32 _pkey;
                              } _addr_pkey;
+                             compat_uptr_t _pad[6];
                      };
+                     u32 _xflags;
              } _sigfault;
 
              /* SIGPOLL */

include/linux/signal_types.h +1 -1

index a7887ad84d36..75ca861d982a 100644
@@ -78,6 +78,6 @@ struct ksignal {
 
 #define UAPI_SA_FLAGS                                                          \
      (SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \
-      SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS)
+      SA_NODEFER | SA_RESETHAND | SA_XFLAGS | __ARCH_UAPI_SA_FLAGS)
 
 #endif /* _LINUX_SIGNAL_TYPES_H */

include/uapi/asm-generic/siginfo.h +4 -0

index 7aacf9389010..8158d5df666a 100644
@@ -91,7 +91,9 @@ union __sifields {
                              char _dummy_pkey[__ADDR_BND_PKEY_PAD];
                              __u32 _pkey;
                      } _addr_pkey;
+                     void *_pad[6];
              };
+             __u32 _xflags;
      } _sigfault;
 
      /* SIGPOLL */

@@ -152,6 +154,8 @@ typedef struct siginfo {
 #define si_trapno    _sifields._sigfault._trapno
 #endif
 #define si_addr_lsb  _sifields._sigfault._addr_lsb
+/* si_xflags is only valid if 0 < si_code < SI_KERNEL */
+#define si_xflags    _sifields._sigfault._xflags
 #define si_lower     _sifields._sigfault._addr_bnd._lower
 #define si_upper     _sifields._sigfault._addr_bnd._upper
 #define si_pkey              _sifields._sigfault._addr_pkey._pkey

include/uapi/asm-generic/signal-defs.h +4 -0

index 0126ebda4d31..cd522819f4ba 100644
@@ -20,6 +20,9 @@
  * so this bit allows flag bit support to be detected from userspace while
  * allowing an old kernel to be distinguished from a kernel that supports every
  * flag bit.
+ * SA_XFLAGS indicates that the signal handler requires the siginfo.si_xflags
+ * field to be valid. Note that if the kernel supports SA_XFLAGS, the field will
+ * be valid regardless of the value of this flag.
  *
  * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
  * Unix names RESETHAND and NODEFER respectively.

@@ -49,6 +52,7 @@
 #define SA_RESETHAND 0x80000000
 #endif
 #define SA_UNSUPPORTED       0x00000400
+#define SA_XFLAGS    0x00000800
 
 #define SA_NOMASK    SA_NODEFER
 #define SA_ONESHOT   SA_RESETHAND

include/uapi/linux/ptrace.h +12 -0

index a71b6e3b03eb..93946edf0139 100644
@@ -101,6 +101,18 @@ struct ptrace_syscall_info {
      };
 };
 
+#define PTRACE_SETSIGINFO2   0x420f
+/*
+ * These flags are passed as the addr argument to ptrace.
+ */
+
+/*
+ * Asserts that the caller is aware of the field siginfo.si_xflags. Prevents
+ * the kernel from automatically setting the field to 0 when the signal uses
+ * a sigfault layout.
+ */
+#define PTRACE_SIGINFO_XFLAGS        0x1
+
 /*
  * These values are stored in task->ptrace_message
  * by tracehook_report_syscall_* to describe the current syscall-stop.

kernel/ptrace.c +18 -4

index 43d6179508d6..85b5b4e38661 100644
@@ -687,18 +687,32 @@ static int ptrace_getsiginfo(struct task_struct *child, kernel_siginfo_t *info)
      return error;
 }
 
-static int ptrace_setsiginfo(struct task_struct *child, const kernel_siginfo_t *info)
+static int ptrace_setsiginfo(struct task_struct *child, unsigned long flags,
+                          kernel_siginfo_t *info)
 {
-     unsigned long flags;
+     unsigned long lock_flags;
      int error = -ESRCH;
 
-     if (lock_task_sighand(child, &flags)) {
+     if (flags & ~PTRACE_SIGINFO_XFLAGS) {
+             return -EINVAL;
+     }
+
+     /*
+      * If the caller is unaware of si_xflags and we're using a layout that
+      * requires it, set it to 0 which means "no fields are available".
+      */
+     if (!(flags & PTRACE_SIGINFO_XFLAGS) &&
+         siginfo_layout_is_fault(
+                 siginfo_layout(info->si_signo, info->si_code)))
+             info->si_xflags = 0;
+
+     if (lock_task_sighand(child, &lock_flags)) {
              error = -EINVAL;
              if (likely(child->last_siginfo != NULL)) {
                      copy_siginfo(child->last_siginfo, info);
                      error = 0;
              }
-             unlock_task_sighand(child, &flags);
+             unlock_task_sighand(child, &lock_flags);
      }
      return error;
 }

kernel/ptrace.c int ptrace_request(struct task_struct *child, long request, · line 1055

Quoted 4 lines

kernel/ptrace.c +1 -0

@@ -1038,9 +1052,12 @@ int ptrace_request(struct task_struct *child, long request,
              break;
 
      case PTRACE_SETSIGINFO:
+             addr = 0;

If this is intended to fall through, please add a

                /* fall through */

comment here (newer GCC has warnings to catch this; not sure about clang, but I'd be surprised if no version warns).

Quoted 30 lines · Dave Martin

Quoted 11 lines · Peter Collingbourne

This field will contain flags that may be used by signal handlers to determine whether other fields in the _sigfault portion of siginfo are valid. An example use case is the following patch, which introduces the si_addr_tag_bits{,_mask} fields.

A new sigcontext flag, SA_XFLAGS, is introduced in order to allow a signal handler to require the kernel to set the field (but note that the field will be set anyway if the kernel supports the flag, regardless of its value). In combination with the previous patches, this allows a userspace program to determine whether the kernel will set the field.

Apologies for this coming rather late:

It occurs to me that we might want a more specific name, since this only applies to fault signals -- say, SA_FAULTFLAGS.

If we end up wanting to add flags fields for other signal types, then we might end up needing a SA_ flag for each, which would be a bit annoying.

So, alternatively. I wonder whether it's worth preemptively adding an extra flags to every kind of kernel-generated siginfo. If so, then having a single SA_XFLAGS would be fine.

If added flags fields all over the place is considered overkill, then I guess it's sufficient to rename this flag.

Quoted 2 lines

If renaming, the actual flags field in siginfo should also be renamed to match.

I'd prefer not to add flags fields to every union member at this point. I agree that faultflags is a better name, and I guess it's one more reason not to try and reuse the ia64 field. Renamed in v13.

Quoted 49 lines

Quoted 42 lines

kernel/ptrace.c +18 -4

index 43d6179508d6..85b5b4e38661 100644
@@ -687,18 +687,32 @@ static int ptrace_getsiginfo(struct task_struct *child, kernel_siginfo_t *info)
      return error;
 }
 
-static int ptrace_setsiginfo(struct task_struct *child, const kernel_siginfo_t *info)
+static int ptrace_setsiginfo(struct task_struct *child, unsigned long flags,
+                          kernel_siginfo_t *info)
 {
-     unsigned long flags;
+     unsigned long lock_flags;
      int error = -ESRCH;
 
-     if (lock_task_sighand(child, &flags)) {
+     if (flags & ~PTRACE_SIGINFO_XFLAGS) {
+             return -EINVAL;
+     }
+
+     /*
+      * If the caller is unaware of si_xflags and we're using a layout that
+      * requires it, set it to 0 which means "no fields are available".
+      */
+     if (!(flags & PTRACE_SIGINFO_XFLAGS) &&
+         siginfo_layout_is_fault(
+                 siginfo_layout(info->si_signo, info->si_code)))
+             info->si_xflags = 0;
+
+     if (lock_task_sighand(child, &lock_flags)) {
              error = -EINVAL;
              if (likely(child->last_siginfo != NULL)) {
                      copy_siginfo(child->last_siginfo, info);
                      error = 0;
              }
-             unlock_task_sighand(child, &flags);
+             unlock_task_sighand(child, &lock_flags);
      }
      return error;
 }

kernel/ptrace.c int ptrace_request(struct task_struct *child, long request, · line 1055

Quoted 4 lines

kernel/ptrace.c +1 -0

@@ -1038,9 +1052,12 @@ int ptrace_request(struct task_struct *child, long request,
              break;
 
      case PTRACE_SETSIGINFO:
+             addr = 0;

If this is intended to fall through, please add a

Quoted 4 lines

                /* fall through */

comment here (newer GCC has warnings to catch this; not sure about clang, but I'd be surprised if no version warns).

Yes, clang has this warning, but it looks like it is currently disabled in clang due to differences between the compilers [1] so I didn't see it.

It looks like the kernel is moving towards using the fallthrough macro/attribute defined in include/linux/compiler_attributes.h (and to me this personally seems better than relying on parsing comments), so I've used that macro in v13.

The kernel currently clears the tag bits (i.e. bits 56-63) in the fault address exposed via siginfo.si_addr and sigcontext.fault_address. However, the tag bits may be needed by tools in order to accurately diagnose memory errors, such as HWASan [1] or future tools based on the Memory Tagging Extension (MTE).

We should not stop clearing these bits in the existing fault address fields, because there may be existing userspace applications that are expecting the tag bits to be cleared. Instead, create a new pair of union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 there, together with a mask specifying which bits are valid.

A flag is added to si_xflags to allow userspace to determine whether the values in the fields are valid.

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446

---
v12:
- add new fields to signal_compat.c test cases
- rebased to 5.10-rc1
- mask out bits 63:60 for tag check faults

v11:
- add a comment explaining what the arch hook should do
- rename ignored bits to tag bits

v10:
- rename the flag to SIXFLAG_ADDR_IGNORED_BITS
- use an arch hook to specify which bits are ignored, instead of passing them explicitly
- while refactoring for the arch hook, noticed that my previous patches missed a case involving cache maintenance instructions, so expose the tag bits for that signal as well

v9:
- make the ignored bits fields generic
- add some new dependent patches that prepare us to store the field in such a way that userspace can detect their presence

v8:
- rebase onto 5.8rc2

v7:
- switch to a new siginfo field instead of using sigcontext
- merge the patch back into one since the other patches are now unnecessary

v6:
- move fault address and fault code into the kernel_siginfo data structure
- split the patch in three since it was getting large and now has generic and arch-specific parts

v5:
- add padding to fault_addr_top_byte_context in order to ensure the correct size and preserve sp alignment

v4:
- expose only the tag bits in the context instead of the entire FAR_EL1
- remove mention of the new context from the sigcontext.__reserved[] note

v3:
- add documentation to tagged-pointers.rst
- update comments in sigcontext.h

v2:
- revert changes to hw_breakpoint.c
- rename set_thread_esr to set_thread_far_esr

 Documentation/arm64/tagged-pointers.rst | 21 +++++---
 arch/arm64/include/asm/exception.h      |  2 +-
 arch/arm64/include/asm/signal.h         | 19 +++++++
 arch/arm64/include/asm/system_misc.h    |  2 +-
 arch/arm64/include/asm/traps.h          |  6 +--
 arch/arm64/kernel/debug-monitors.c      |  5 +-
 arch/arm64/kernel/entry-common.c        |  2 -
 arch/arm64/kernel/ptrace.c              |  7 +--
 arch/arm64/kernel/sys_compat.c          |  5 +-
 arch/arm64/kernel/traps.c               | 29 ++++++-----
 arch/arm64/mm/fault.c                   | 68 ++++++++++++++-----------
 arch/x86/kernel/signal_compat.c         |  9 +++-
 include/linux/compat.h                  |  2 +
 include/linux/signal.h                  | 16 ++++++
 include/uapi/asm-generic/siginfo.h      | 10 ++++
 kernel/signal.c                         | 18 ++++++-
 16 files changed, 148 insertions(+), 73 deletions(-)
 create mode 100644 arch/arm64/include/asm/signal.h

Documentation/arm64/tagged-pointers.rst +15 -6

index eab4323609b9..032c09a876f4 100644
@@ -53,12 +53,21 @@ visibility.
 Preserving tags
 ---------------
 
-Non-zero tags are not preserved when delivering signals. This means that
-signal handlers in applications making use of tags cannot rely on the
-tag information for user virtual addresses being maintained for fields
-inside siginfo_t. One exception to this rule is for signals raised in
-response to watchpoint debug exceptions, where the tag information will
-be preserved.
+Non-zero tags are not preserved in the fault address fields
+siginfo.si_addr or sigcontext.fault_address when delivering
+signals. This means that signal handlers in applications making use
+of tags cannot rely on the tag information for user virtual addresses
+being maintained in these fields. One exception to this rule is for
+signals raised in response to watchpoint debug exceptions, where the
+tag information will be preserved.
+
+The fault address tag is preserved in the si_addr_tag_bits field
+of siginfo, which is set for signals raised in response to data aborts
+and instruction aborts. The si_addr_tag_bits_mask field indicates
+which bits of the field are valid. The validity of these fields is
+indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags,
+and the validity of si_xflags in turn is indicated by the kernel
+indicating support for the sigaction.sa_flags flag SA_XFLAGS.
 
 The architecture prevents the use of a tagged PC, so the upper byte will
 be set to a sign-extension of bit 55 on exception return.

arch/arm64/include/asm/exception.h +1 -1

index 99b9383cd036..2a8aa1884d8a 100644
@@ -32,7 +32,7 @@ static inline u32 disr_to_esr(u64 disr)
 }
 
 asmlinkage void enter_from_user_mode(void);
-void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs);
+void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs);
 void do_undefinstr(struct pt_regs *regs);
 void do_bti(struct pt_regs *regs);
 asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr);

arch/arm64/include/asm/signal.h new file +4 -0

new file mode 100644
index 000000000000..46f9b3c61896
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_ASM_SIGNAL_H
+#define __ARM64_ASM_SIGNAL_H
+

Quoted 145 lines · Peter Collingbourne

The kernel currently clears the tag bits (i.e. bits 56-63) in the fault address exposed via siginfo.si_addr and sigcontext.fault_address. However, the tag bits may be needed by tools in order to accurately diagnose memory errors, such as HWASan [1] or future tools based on the Memory Tagging Extension (MTE).

We should not stop clearing these bits in the existing fault address fields, because there may be existing userspace applications that are expecting the tag bits to be cleared. Instead, create a new pair of union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 there, together with a mask specifying which bits are valid.

A flag is added to si_xflags to allow userspace to determine whether the values in the fields are valid.

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446

---
v12:
- add new fields to signal_compat.c test cases
- rebased to 5.10-rc1
- mask out bits 63:60 for tag check faults

v11:
- add a comment explaining what the arch hook should do
- rename ignored bits to tag bits

v10:
- rename the flag to SIXFLAG_ADDR_IGNORED_BITS
- use an arch hook to specify which bits are ignored, instead of passing them explicitly
- while refactoring for the arch hook, noticed that my previous patches missed a case involving cache maintenance instructions, so expose the tag bits for that signal as well

v9:
- make the ignored bits fields generic
- add some new dependent patches that prepare us to store the field in such a way that userspace can detect their presence

v8:
- rebase onto 5.8rc2

v7:
- switch to a new siginfo field instead of using sigcontext
- merge the patch back into one since the other patches are now unnecessary

v6:
- move fault address and fault code into the kernel_siginfo data structure
- split the patch in three since it was getting large and now has generic and arch-specific parts

v5:
- add padding to fault_addr_top_byte_context in order to ensure the correct size and preserve sp alignment

v4:
- expose only the tag bits in the context instead of the entire FAR_EL1
- remove mention of the new context from the sigcontext.__reserved[] note

v3:
- add documentation to tagged-pointers.rst
- update comments in sigcontext.h

v2:
- revert changes to hw_breakpoint.c
- rename set_thread_esr to set_thread_far_esr

 Documentation/arm64/tagged-pointers.rst | 21 +++++---
 arch/arm64/include/asm/exception.h      |  2 +-
 arch/arm64/include/asm/signal.h         | 19 +++++++
 arch/arm64/include/asm/system_misc.h    |  2 +-
 arch/arm64/include/asm/traps.h          |  6 +--
 arch/arm64/kernel/debug-monitors.c      |  5 +-
 arch/arm64/kernel/entry-common.c        |  2 -
 arch/arm64/kernel/ptrace.c              |  7 +--
 arch/arm64/kernel/sys_compat.c          |  5 +-
 arch/arm64/kernel/traps.c               | 29 ++++++-----
 arch/arm64/mm/fault.c                   | 68 ++++++++++++++-----------
 arch/x86/kernel/signal_compat.c         |  9 +++-
 include/linux/compat.h                  |  2 +
 include/linux/signal.h                  | 16 ++++++
 include/uapi/asm-generic/siginfo.h      | 10 ++++
 kernel/signal.c                         | 18 ++++++-
 16 files changed, 148 insertions(+), 73 deletions(-)
 create mode 100644 arch/arm64/include/asm/signal.h

Documentation/arm64/tagged-pointers.rst +15 -6

index eab4323609b9..032c09a876f4 100644
@@ -53,12 +53,21 @@ visibility.
 Preserving tags
 ---------------
 
-Non-zero tags are not preserved when delivering signals. This means that
-signal handlers in applications making use of tags cannot rely on the
-tag information for user virtual addresses being maintained for fields
-inside siginfo_t. One exception to this rule is for signals raised in
-response to watchpoint debug exceptions, where the tag information will
-be preserved.
+Non-zero tags are not preserved in the fault address fields
+siginfo.si_addr or sigcontext.fault_address when delivering
+signals. This means that signal handlers in applications making use
+of tags cannot rely on the tag information for user virtual addresses
+being maintained in these fields. One exception to this rule is for
+signals raised in response to watchpoint debug exceptions, where the
+tag information will be preserved.
+
+The fault address tag is preserved in the si_addr_tag_bits field
+of siginfo, which is set for signals raised in response to data aborts
+and instruction aborts. The si_addr_tag_bits_mask field indicates
+which bits of the field are valid. The validity of these fields is
+indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags,
+and the validity of si_xflags in turn is indicated by the kernel
+indicating support for the sigaction.sa_flags flag SA_XFLAGS.
 
 The architecture prevents the use of a tagged PC, so the upper byte will
 be set to a sign-extension of bit 55 on exception return.

arch/arm64/include/asm/exception.h +1 -1

index 99b9383cd036..2a8aa1884d8a 100644
@@ -32,7 +32,7 @@ static inline u32 disr_to_esr(u64 disr)
 }
 
 asmlinkage void enter_from_user_mode(void);
-void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs);
+void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs);
 void do_undefinstr(struct pt_regs *regs);
 void do_bti(struct pt_regs *regs);
 asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr);

arch/arm64/include/asm/signal.h new file +4 -0

new file mode 100644
index 000000000000..46f9b3c61896
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_ASM_SIGNAL_H
+#define __ARM64_ASM_SIGNAL_H
+

arch/arm64/include/asm/signal.h line 14

Quoted 10 lines

arch/arm64/include/asm/signal.h new file +10 -0

+#include <uapi/asm/signal.h>
+#include <uapi/asm/siginfo.h>
+
+static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig,
+                                                 unsigned long si_code)
+{
+     if (sig == SIGTRAP && si_code == TRAP_BRKPT)
+             return 0;
+     if (sig == SIGSEGV && si_code == SEGV_MTESERR)
+             return 0xfUL << 56;

Should this be 0xffUL << 56?

I thought MTE ignored bits 63:60, rather than requiring them to be 0?

The whole tag byte may be relevant for debugging purposes, even if only some of the bits are checked in hardware.

For consistency, I wonder whether it makes sense to expose the bits as tag bits for watchpoint execeptions, even if they are left un-cleared in si_addr for historical reasons.

Quoted 160 lines · Dave Martin

Quoted 145 lines · Peter Collingbourne

The kernel currently clears the tag bits (i.e. bits 56-63) in the fault address exposed via siginfo.si_addr and sigcontext.fault_address. However, the tag bits may be needed by tools in order to accurately diagnose memory errors, such as HWASan [1] or future tools based on the Memory Tagging Extension (MTE).

We should not stop clearing these bits in the existing fault address fields, because there may be existing userspace applications that are expecting the tag bits to be cleared. Instead, create a new pair of union fields in siginfo._sigfault, and store the tag bits of FAR_EL1 there, together with a mask specifying which bits are valid.

A flag is added to si_xflags to allow userspace to determine whether the values in the fields are valid.

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446

---
v12:
- add new fields to signal_compat.c test cases
- rebased to 5.10-rc1
- mask out bits 63:60 for tag check faults

v11:
- add a comment explaining what the arch hook should do
- rename ignored bits to tag bits

v10:
- rename the flag to SIXFLAG_ADDR_IGNORED_BITS
- use an arch hook to specify which bits are ignored, instead of passing them explicitly
- while refactoring for the arch hook, noticed that my previous patches missed a case involving cache maintenance instructions, so expose the tag bits for that signal as well

v9:
- make the ignored bits fields generic
- add some new dependent patches that prepare us to store the field in such a way that userspace can detect their presence

v8:
- rebase onto 5.8rc2

v7:
- switch to a new siginfo field instead of using sigcontext
- merge the patch back into one since the other patches are now unnecessary

v6:
- move fault address and fault code into the kernel_siginfo data structure
- split the patch in three since it was getting large and now has generic and arch-specific parts

v5:
- add padding to fault_addr_top_byte_context in order to ensure the correct size and preserve sp alignment

v4:
- expose only the tag bits in the context instead of the entire FAR_EL1
- remove mention of the new context from the sigcontext.__reserved[] note

v3:
- add documentation to tagged-pointers.rst
- update comments in sigcontext.h

v2:
- revert changes to hw_breakpoint.c
- rename set_thread_esr to set_thread_far_esr

 Documentation/arm64/tagged-pointers.rst | 21 +++++---
 arch/arm64/include/asm/exception.h      |  2 +-
 arch/arm64/include/asm/signal.h         | 19 +++++++
 arch/arm64/include/asm/system_misc.h    |  2 +-
 arch/arm64/include/asm/traps.h          |  6 +--
 arch/arm64/kernel/debug-monitors.c      |  5 +-
 arch/arm64/kernel/entry-common.c        |  2 -
 arch/arm64/kernel/ptrace.c              |  7 +--
 arch/arm64/kernel/sys_compat.c          |  5 +-
 arch/arm64/kernel/traps.c               | 29 ++++++-----
 arch/arm64/mm/fault.c                   | 68 ++++++++++++++-----------
 arch/x86/kernel/signal_compat.c         |  9 +++-
 include/linux/compat.h                  |  2 +
 include/linux/signal.h                  | 16 ++++++
 include/uapi/asm-generic/siginfo.h      | 10 ++++
 kernel/signal.c                         | 18 ++++++-
 16 files changed, 148 insertions(+), 73 deletions(-)
 create mode 100644 arch/arm64/include/asm/signal.h

Documentation/arm64/tagged-pointers.rst +15 -6

index eab4323609b9..032c09a876f4 100644
@@ -53,12 +53,21 @@ visibility.
 Preserving tags
 ---------------
 
-Non-zero tags are not preserved when delivering signals. This means that
-signal handlers in applications making use of tags cannot rely on the
-tag information for user virtual addresses being maintained for fields
-inside siginfo_t. One exception to this rule is for signals raised in
-response to watchpoint debug exceptions, where the tag information will
-be preserved.
+Non-zero tags are not preserved in the fault address fields
+siginfo.si_addr or sigcontext.fault_address when delivering
+signals. This means that signal handlers in applications making use
+of tags cannot rely on the tag information for user virtual addresses
+being maintained in these fields. One exception to this rule is for
+signals raised in response to watchpoint debug exceptions, where the
+tag information will be preserved.
+
+The fault address tag is preserved in the si_addr_tag_bits field
+of siginfo, which is set for signals raised in response to data aborts
+and instruction aborts. The si_addr_tag_bits_mask field indicates
+which bits of the field are valid. The validity of these fields is
+indicated by the SIXFLAG_ADDR_TAG_BITS flag in siginfo.si_xflags,
+and the validity of si_xflags in turn is indicated by the kernel
+indicating support for the sigaction.sa_flags flag SA_XFLAGS.
 
 The architecture prevents the use of a tagged PC, so the upper byte will
 be set to a sign-extension of bit 55 on exception return.

arch/arm64/include/asm/exception.h +1 -1

index 99b9383cd036..2a8aa1884d8a 100644
@@ -32,7 +32,7 @@ static inline u32 disr_to_esr(u64 disr)
 }
 
 asmlinkage void enter_from_user_mode(void);
-void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs);
+void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs);
 void do_undefinstr(struct pt_regs *regs);
 void do_bti(struct pt_regs *regs);
 asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr);

arch/arm64/include/asm/signal.h new file +4 -0

new file mode 100644
index 000000000000..46f9b3c61896
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_ASM_SIGNAL_H
+#define __ARM64_ASM_SIGNAL_H
+

arch/arm64/include/asm/signal.h line 14

Quoted 10 lines

arch/arm64/include/asm/signal.h new file +10 -0

+#include <uapi/asm/signal.h>
+#include <uapi/asm/siginfo.h>
+
+static inline unsigned long arch_addr_tag_bits_mask(unsigned long sig,
+                                                 unsigned long si_code)
+{
+     if (sig == SIGTRAP && si_code == TRAP_BRKPT)
+             return 0;
+     if (sig == SIGSEGV && si_code == SEGV_MTESERR)
+             return 0xfUL << 56;

Should this be 0xffUL << 56?

Quoted 1 line

I thought MTE ignored bits 63:60, rather than requiring them to be 0?

Yes, but the architecture defines FAR_EL1[63:60] as UNKNOWN for tag check faults. As such the bits are masked out in do_tag_check_fault and excluded from the mask here to indicate that they are not present.

Quoted 3 lines

The whole tag byte may be relevant for debugging purposes, even if only some of the bits are checked in hardware.

Yes and that's why it's a bit of a shame that the bits were defined as UNKNOWN. We had an idea for how to improve error reports by using those bits to link tag check faults to previous allocations, which was precluded by the missing bits.

Hopefully a future revision of the architecture will define these bits for tag check faults (at least optionally). If that ever happens and support for the architecture extension is detected we could stop masking the bits out in do_tag_check_fault and set si_addr_tag_bits_mask to 0xffUL << 56, which would let userspace know that the bits are now present.

Quoted 3 lines

For consistency, I wonder whether it makes sense to expose the bits as tag bits for watchpoint execeptions, even if they are left un-cleared in si_addr for historical reasons.

I don't have a strong opinion on whether to do this or not, but it seems like a nice property that the bits are either defined in si_addr or in si_addr_tag_bits. I think we could leave the watchpoint exception on arm64 as "weird for historical reasons" and insist that any future architectures adopting tagged addresses handle the tag bits uniformly.