Patch "x86/io: Add "memory" clobber to insb/insw/insl/outsb/outsw/outsl" has been added to the 4.4-stable tree

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

x86/io: Add "memory" clobber to insb/insw/insl/outsb/outsw/outsl

to the 4.4-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:
x86-io-add-memory-clobber-to-insb-insw-insl-outsb-outsw-outsl.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Arnd Bergmann <[email protected]>
Date: Wed, 19 Jul 2017 14:53:02 +0200
Subject: x86/io: Add "memory" clobber to insb/insw/insl/outsb/outsw/outsl
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From: Arnd Bergmann <[email protected]>

commit 7206f9bf108eb9513d170c73f151367a1bdf3dbf upstream.

The x86 version of insb/insw/insl uses an inline assembly that does not have the target buffer listed as an output. This can confuse the compiler, leading it to think that a subsequent access of the buffer is uninitialized:

drivers/net/wireless/wl3501_cs.c: In function ‘wl3501_mgmt_scan_confirm’:
drivers/net/wireless/wl3501_cs.c:665:9: error: ‘sig.status’ is used uninitialized in this function [-Werror=uninitialized] drivers/net/wireless/wl3501_cs.c:668:12: error: ‘sig.cap_info’ may be used uninitialized in this function [-Werror=maybe-uninitialized] drivers/net/sb1000.c: In function 'sb1000_rx':
drivers/net/sb1000.c:775:9: error: 'st[0]' is used uninitialized in this function [-Werror=uninitialized] drivers/net/sb1000.c:776:10: error: 'st[1]' may be used uninitialized in this function [-Werror=maybe-uninitialized] drivers/net/sb1000.c:784:11: error: 'st[1]' may be used uninitialized in this function [-Werror=maybe-uninitialized]

I tried to mark the exact input buffer as an output here, but couldn't figure it out. As suggested by Linus, marking all memory as clobbered however is good enough too. For the outs operations, I also add the memory clobber, to force the input to be written to local variables. This is probably already guaranteed by the "asm volatile", but it can't hurt to do this for symmetry.

---
 arch/x86/include/asm/io.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -304,13 +304,13 @@ static inline unsigned type in##bwl##_p(
 static inline void outs##bwl(int port, const void *addr, unsigned long count) \
 {									\
 	asm volatile("rep; outs" #bwl					\
-		     : "+S"(addr), "+c"(count) : "d"(port));		\
+		     : "+S"(addr), "+c"(count) : "d"(port) : "memory");	\
 }									\
 									\
 static inline void ins##bwl(int port, void *addr, unsigned long count)	\
 {									\
 	asm volatile("rep; ins" #bwl					\
-		     : "+D"(addr), "+c"(count) : "d"(port));		\
+		     : "+D"(addr), "+c"(count) : "d"(port) : "memory");	\
 }
 
 BUILDIO(b, b, char)

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

queue-4.4/x86-io-add-memory-clobber-to-insb-insw-insl-outsb-outsw-outsl.patch queue-4.4/scsi-isci-avoid-array-subscript-warning.patch