Patch "arm64: compat: fix stxr failure case in SWP emulation" has been added to the 4.2-stable tree

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

arm64: compat: fix stxr failure case in SWP emulation

to the 4.2-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:
arm64-compat-fix-stxr-failure-case-in-swp-emulation.patch
and it can be found in the queue-4.2 subdirectory.

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

From: Will Deacon <[email protected]>
Date: Thu, 15 Oct 2015 13:55:53 +0100
Subject: arm64: compat: fix stxr failure case in SWP emulation

From: Will Deacon <[email protected]>

commit 589cb22bbedacf325951014c07a35a2b01ca57f6 upstream.

If the STXR instruction fails in the SWP emulation code, we leave *data overwritten with the loaded value, therefore corrupting the data written by a subsequent, successful attempt.

This patch re-jigs the code so that we only write back to *data once we know that the update has happened.

---
 arch/arm64/kernel/armv8_deprecated.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

@@ -279,22 +279,24 @@ static void register_insn_emulation_sysc
  */
 #define __user_swpX_asm(data, addr, res, temp, B)		\
 	__asm__ __volatile__(					\
-	"	mov		%w2, %w1\n"			\
-	"0:	ldxr"B"		%w1, [%3]\n"			\
-	"1:	stxr"B"		%w0, %w2, [%3]\n"		\
+	"0:	ldxr"B"		%w2, [%3]\n"			\
+	"1:	stxr"B"		%w0, %w1, [%3]\n"		\
 	"	cbz		%w0, 2f\n"			\
 	"	mov		%w0, %w4\n"			\
+	"	b		3f\n"				\
 	"2:\n"							\
+	"	mov		%w1, %w2\n"			\
+	"3:\n"							\
 	"	.pushsection	 .fixup,\"ax\"\n"		\
 	"	.align		2\n"				\
-	"3:	mov		%w0, %w5\n"			\
-	"	b		2b\n"				\
+	"4:	mov		%w0, %w5\n"			\
+	"	b		3b\n"				\
 	"	.popsection"					\
 	"	.pushsection	 __ex_table,\"a\"\n"		\
 	"	.align		3\n"				\
-	"	.quad		0b, 3b\n"			\
-	"	.quad		1b, 3b\n"			\
-	"	.popsection"					\
+	"	.quad		0b, 4b\n"			\
+	"	.quad		1b, 4b\n"			\
+	"	.popsection\n"					\
 	: "=&r" (res), "+r" (data), "=&r" (temp)		\
 	: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)		\
 	: "memory")

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

queue-4.2/arm64-kernel-fix-tcr_el1.t0sz-restore-on-systems-with-extended-idmap.patch queue-4.2/arm64-compat-fix-stxr-failure-case-in-swp-emulation.patch queue-4.2/revert-arm64-unwind-fix-pc-calculation.patch