Patch "arm: kprobes: Align stack to 8-bytes in test code" has been added to the 4.9-stable tree

Patch "arm: kprobes: Align stack to 8-bytes in test code" has been added to the 4.9-stable tree

[gregkh]

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

    arm: kprobes: Align stack to 8-bytes in test code

to the 4.9-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:
     arm-kprobes-align-stack-to-8-bytes-in-test-code.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Dec 21 09:02:40 CET 2017
From: Jon Medhurst <tixy@linaro.org>
Date: Thu, 2 Mar 2017 13:04:09 +0000
Subject: arm: kprobes: Align stack to 8-bytes in test code

From: Jon Medhurst <tixy@linaro.org>


[ Upstream commit 974310d047f3c7788a51d10c8d255eebdb1fa857 ]

kprobes test cases need to have a stack that is aligned to an 8-byte
boundary because they call other functions (and the ARM ABI mandates
that alignment) and because test cases include 64-bit accesses to the
stack. Unfortunately, GCC doesn't ensure this alignment for inline
assembler and for the code in question seems to always misalign it by
pushing just the LR register onto the stack. We therefore need to
explicitly perform stack alignment at the start of each test case.

Without this fix, some test cases will generate alignment faults on
systems where alignment is enforced. Even if the kernel is configured to
handle these faults in software, triggering them is ugly. It also
exposes limitations in the fault handling code which doesn't cope with
writes to the stack. E.g. when handling this instruction

   strd r6, [sp, #-64]!

the fault handling code will write to a stack location below the SP
value at the point the fault occurred, which coincides with where the
exception handler has pushed the saved register context. This results in
corruption of those registers.

Signed-off-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm/probes/kprobes/test-core.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/arch/arm/probes/kprobes/test-core.c
+++ b/arch/arm/probes/kprobes/test-core.c
@@ -976,7 +976,10 @@ static void coverage_end(void)
 void __naked __kprobes_test_case_start(void)
 {
 	__asm__ __volatile__ (
-		"stmdb	sp!, {r4-r11}				\n\t"
+		"mov	r2, sp					\n\t"
+		"bic	r3, r2, #7				\n\t"
+		"mov	sp, r3					\n\t"
+		"stmdb	sp!, {r2-r11}				\n\t"
 		"sub	sp, sp, #"__stringify(TEST_MEMORY_SIZE)"\n\t"
 		"bic	r0, lr, #1  @ r0 = inline data		\n\t"
 		"mov	r1, sp					\n\t"
@@ -996,7 +999,8 @@ void __naked __kprobes_test_case_end_32(
 		"movne	pc, r0					\n\t"
 		"mov	r0, r4					\n\t"
 		"add	sp, sp, #"__stringify(TEST_MEMORY_SIZE)"\n\t"
-		"ldmia	sp!, {r4-r11}				\n\t"
+		"ldmia	sp!, {r2-r11}				\n\t"
+		"mov	sp, r2					\n\t"
 		"mov	pc, r0					\n\t"
 	);
 }
@@ -1012,7 +1016,8 @@ void __naked __kprobes_test_case_end_16(
 		"bxne	r0					\n\t"
 		"mov	r0, r4					\n\t"
 		"add	sp, sp, #"__stringify(TEST_MEMORY_SIZE)"\n\t"
-		"ldmia	sp!, {r4-r11}				\n\t"
+		"ldmia	sp!, {r2-r11}				\n\t"
+		"mov	sp, r2					\n\t"
 		"bx	r0					\n\t"
 	);
 }


Patches currently in stable-queue which might be from tixy@linaro.org are

queue-4.9/arm-kprobes-fix-the-return-address-of-multiple-kretprobes.patch
queue-4.9/arm-kprobes-align-stack-to-8-bytes-in-test-code.patch