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Message-ID: <lsq.1500213406.779816183@decadent.org.uk>
Date: Sun, 16 Jul 2017 14:56:46 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org,
"Martin Schwidefsky" <schwidefsky@...ibm.com>,
"Heiko Carstens" <heiko.carstens@...ibm.com>,
"Al Viro" <viro@...iv.linux.org.uk>
Subject: [PATCH 3.16 101/178] s390/uaccess: get_user() should zero on
failure (again)
3.16.46-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Heiko Carstens <heiko.carstens@...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@...iv.linux.org.uk>
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
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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