Patch "signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Eric W. Biederman" <[email protected]>
Date: Sat, 19 Aug 2017 15:26:01 -0500
Subject: signal/powerpc: Document conflicts with SI_USER and SIGFPE and SIGTRAP

From: "Eric W. Biederman" <[email protected]>

[ Upstream commit cf4674c46c66e45f238f8f7e81af2a444b970c0a ]

Setting si_code to 0 results in a userspace seeing an si_code of 0. This is the same si_code as SI_USER. Posix and common sense requires that SI_USER not be a signal specific si_code. As such this use of 0 for the si_code is a pretty horribly broken ABI.

Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a value of __SI_KILL and now sees a value of SIL_KILL with the result that uid and pid fields are copied and which might copying the si_addr field by accident but certainly not by design. Making this a very flakey implementation.

Utilizing FPE_FIXME and TRAP_FIXME, siginfo_layout() will now return SIL_FAULT and the appropriate fields will be reliably copied.

Possible ABI fixes includee:
- Send the signal without siginfo
- Don't generate a signal
- Possibly assign and use an appropriate si_code
- Don't handle cases which can't happen
Cc: Paul Mackerras <[email protected]>
Cc: Kumar Gala <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: [email protected]
Ref: 9bad068c24d7 ("[PATCH] ppc32: support for e500 and 85xx")
Ref: 0ed70f6105ef ("PPC32: Provide proper siginfo information on various exceptions.") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git

---
 arch/powerpc/include/uapi/asm/siginfo.h |   15 +++++++++++++++
 arch/powerpc/kernel/traps.c             |   10 +++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)

@@ -18,4 +18,19 @@
 #undef NSIGTRAP
 #define NSIGTRAP	4
 
+/*
+ * SIGFPE si_codes
+ */
+#ifdef __KERNEL__
+#define FPE_FIXME	0	/* Broken dup of SI_USER */
+#endif /* __KERNEL__ */
+
+/*
+ * SIGTRAP si_codes
+ */
+#ifdef __KERNEL__
+#define TRAP_FIXME	0	/* Broken dup of SI_USER */
+#endif /* __KERNEL__ */
+
+
 #endif	/* _ASM_POWERPC_SIGINFO_H */

@@ -720,7 +720,7 @@ void unknown_exception(struct pt_regs *r
 	printk("Bad trap at PC: %lx, SR: %lx, vector=%lx\n",
 	       regs->nip, regs->msr, regs->trap);
 
-	_exception(SIGTRAP, regs, 0, 0);
+	_exception(SIGTRAP, regs, TRAP_FIXME, 0);
 
 	exception_exit(prev_state);
 }

@@ -742,7 +742,7 @@ bail:
 
 void RunModeException(struct pt_regs *regs)
 {
-	_exception(SIGTRAP, regs, 0, 0);
+	_exception(SIGTRAP, regs, TRAP_FIXME, 0);
 }
 
 void single_step_exception(struct pt_regs *regs)

@@ -781,7 +781,7 @@ static void emulate_single_step(struct p
 
 static inline int __parse_fpscr(unsigned long fpscr)
 {
-	int ret = 0;
+	int ret = FPE_FIXME;
 
 	/* Invalid operation */
 	if ((fpscr & FPSCR_VE) && (fpscr & FPSCR_VX))

@@ -1769,7 +1769,7 @@ void SPEFloatingPointException(struct pt
 	extern int do_spe_mathemu(struct pt_regs *regs);
 	unsigned long spefscr;
 	int fpexc_mode;
-	int code = 0;
+	int code = FPE_FIXME;
 	int err;
 
 	flush_spe_to_thread(current);

@@ -1838,7 +1838,7 @@ void SPEFloatingPointRoundException(stru
 		printk(KERN_ERR "unrecognized spe instruction "
 		       "in %s at %lx\n", current->comm, regs->nip);
 	} else {
-		_exception(SIGFPE, regs, 0, regs->nip);
+		_exception(SIGFPE, regs, FPE_FIXME, regs->nip);
 		return;
 	}
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch queue-4.14/signal-arm-document-conflicts-with-si_user-and-sigfpe.patch queue-4.14/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch