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

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@linux-foundation.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.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@kernel.org>

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 7afb0e2f07f40d69ccbe44a70baea52bc70ef685..48febf07e828099d0580be40ad82a8baee6ade18 100644 (file)
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -328,13 +328,13 @@ 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)