linux-kernel - [PATCH 3.10 089/139] x86/io: Add "memory" clobber to insb/insw/insl/outsb/outsw/outsl

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Date:   Wed,  1 Nov 2017 22:26:30 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...nel.org>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 089/139] x86/io: Add "memory" clobber to insb/insw/insl/outsb/outsw/outsl

From: Arnd Bergmann <arnd@...db.de>

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.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tom Lendacky <thomas.lendacky@....com>
Link: http://lkml.kernel.org/r/20170719125310.2487451-5-arnd@arndb.de
Link: https://lkml.org/lkml/2017/7/12/605
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/include/asm/io.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index d8e8eef..86ec87d 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -296,13 +296,13 @@ static inline unsigned type in##bwl##_p(int port)			\
 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)
-- 
2.8.0.rc2.1.gbe9624a