FAILED: patch "[PATCH] s390/ftrace: use expoline for indirect branches" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message May 20, 2018

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2018-05-20 08:30 UTC #0 lore raw

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 23a4d7fd34856da8218c4cfc23dba7a6ec0a423a Mon Sep 17 00:00:00 2001

From: Martin Schwidefsky <[email protected]>
Date: Wed, 25 Apr 2018 18:35:26 +0200
Subject: [PATCH] s390/ftrace: use expoline for indirect branches

The return from the ftrace_stub, _mcount, ftrace_caller and return_to_handler functions is done with "br %r14" and "br %r1". These are indirect branches as well and need to use execute trampolines for CONFIG_EXPOLINE=y.

The ftrace_caller function is a special case as it returns to the start of a function and may only use %r0 and %r1. For a pre z10 machine the standard execute trampoline uses a LARL + EX to do this, but this requires *two* registers in the range %r1..%r15. To get around this the 'br %r1' located in the lowcore is used, then the EX instruction does not need an address register. But the lowcore trick may only be used for pre z14 machines, with noexec=on the mapping for the first page may not contain instructions. The solution for that is an ALTERNATIVE in the expoline THUNK generated by 'GEN_BR_THUNK %r1' to switch to EXRL, this relies on the fact that a machine that supports noexec=on has EXRL as well.

Cc [email protected] # 4.16

Fixes f19fbd5ed6 ("s390: introduce execute-trampolines for branches")

Signed-off-by Martin Schwidefsky <[email protected]>

arch/s390/include/asm/nospec-insn.h +12 -0

index 440689cbcf51..7d7640e1cf90 100644
@@ -2,12 +2,16 @@
 #ifndef _ASM_S390_NOSPEC_ASM_H
 #define _ASM_S390_NOSPEC_ASM_H
 
+#include <asm/alternative-asm.h>
+#include <asm/asm-offsets.h>
 #include <asm/dwarf.h>
 
 #ifdef __ASSEMBLY__
 
 #ifdef CONFIG_EXPOLINE
 
+_LC_BR_R1 = __LC_BR_R1
+
 /*
  * The expoline macros are used to create thunks in the same format
  * as gcc generates them. The 'comdat' section flag makes sure that

@@ -78,13 +82,21 @@
 	.endm
 
 	.macro __THUNK_EX_BR reg,ruse
+	# Be very careful when adding instructions to this macro!
+	# The ALTERNATIVE replacement code has a .+10 which targets
+	# the "br \reg" after the code has been patched.
 #ifdef CONFIG_HAVE_MARCH_Z10_FEATURES
 	exrl	0,555f
 	j	.
 #else
+	.ifc \reg,%r1
+	ALTERNATIVE "ex %r0,_LC_BR_R1", ".insn ril,0xc60000000000,0,.+10", 35
+	j	.
+	.else
 	larl	\ruse,555f
 	ex	0,0(\ruse)
 	j	.
+	.endif
 #endif
 555:	br	\reg
 	.endm

arch/s390/kernel/asm-offsets.c +1 -0

index eb2a5c0443cd..11aea745a2a6 100644
@@ -181,6 +181,7 @@ int main(void)
 	OFFSET(__LC_MACHINE_FLAGS, lowcore, machine_flags);
 	OFFSET(__LC_PREEMPT_COUNT, lowcore, preempt_count);
 	OFFSET(__LC_GMAP, lowcore, gmap);
+	OFFSET(__LC_BR_R1, lowcore, br_r1_trampoline);
 	/* software defined ABI-relevant lowcore locations 0xe00 - 0xe20 */
 	OFFSET(__LC_DUMP_REIPL, lowcore, ipib);
 	/* hardware defined lowcore locations 0x1000 - 0x18ff */

arch/s390/kernel/mcount.S +9 -5

index 82df7d80fab2..27110f3294ed 100644
@@ -9,13 +9,17 @@
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
 #include <asm/ftrace.h>
+#include <asm/nospec-insn.h>
 #include <asm/ptrace.h>
 #include <asm/export.h>
 
+	GEN_BR_THUNK %r1
+	GEN_BR_THUNK %r14
+
 	.section .kprobes.text, "ax"
 
 ENTRY(ftrace_stub)
-	br	%r14
+	BR_EX	%r14
 
 #define STACK_FRAME_SIZE  (STACK_FRAME_OVERHEAD + __PT_SIZE)
 #define STACK_PTREGS	  (STACK_FRAME_OVERHEAD)

@@ -23,7 +27,7 @@ ENTRY(ftrace_stub)
 #define STACK_PTREGS_PSW  (STACK_PTREGS + __PT_PSW)
 
 ENTRY(_mcount)
-	br	%r14
+	BR_EX	%r14
 
 EXPORT_SYMBOL(_mcount)

@@ -53,7 +57,7 @@ ENTRY(ftrace_caller)
 #endif
 	lgr	%r3,%r14
 	la	%r5,STACK_PTREGS(%r15)
-	basr	%r14,%r1
+	BASR_EX	%r14,%r1
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 # The j instruction gets runtime patched to a nop instruction.
 # See ftrace_enable_ftrace_graph_caller.

@@ -68,7 +72,7 @@ ftrace_graph_caller_end:
 #endif
 	lg	%r1,(STACK_PTREGS_PSW+8)(%r15)
 	lmg	%r2,%r15,(STACK_PTREGS_GPRS+2*8)(%r15)
-	br	%r1
+	BR_EX	%r1
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER

@@ -81,6 +85,6 @@ ENTRY(return_to_handler)
 	aghi	%r15,STACK_FRAME_OVERHEAD
 	lgr	%r14,%r2
 	lmg	%r2,%r5,32(%r15)
-	br	%r14
+	BR_EX	%r14
 
 #endif