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Subject[PATCH 3.18 029/124] s390/uaccess: get_user() should zero on failure (again)
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Heiko Carstens <heiko.carstens@de.ibm.com>

commit d09c5373e8e4eaaa09233552cbf75dc4c4f21203 upstream.

Commit fd2d2b191fe7 ("s390: get_user() should zero on failure")
intended to fix s390's get_user() implementation which did not zero
the target operand if the read from user space faulted. Unfortunately
the patch has no effect: the corresponding inline assembly specifies
that the operand is only written to ("=") and the previous value is
discarded.

Therefore the compiler is free to and actually does omit the zero
initialization.

To fix this simply change the contraint modifier to "+", so the
compiler cannot omit the initialization anymore.

Fixes: c9ca78415ac1 ("s390/uaccess: provide inline variants of get_user/put_user")
Fixes: fd2d2b191fe7 ("s390: get_user() should zero on failure")
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/include/asm/uaccess.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -148,7 +148,7 @@ unsigned long __must_check __copy_to_use
" jg 2b\n" \
".popsection\n" \
EX_TABLE(0b,3b) EX_TABLE(1b,3b) \
- : "=d" (__rc), "=Q" (*(to)) \
+ : "=d" (__rc), "+Q" (*(to)) \
: "d" (size), "Q" (*(from)), \
"d" (__reg0), "K" (-EFAULT) \
: "cc"); \

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