s390/uaccess: get_user() should zero on failure (again)

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commit d09c5373e8 upstream.

Commit fd2d2b191f ("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: c9ca78415a ("s390/uaccess: provide inline variants of get_user/put_user")
Fixes: fd2d2b191f ("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>

...

This commit is contained in:

Heiko Carstens 2017-03-27 09:48:04 +02:00 • committed by Greg Kroah-Hartman

parent f4938792af

commit 7b68273f79

1 changed files with 1 additions and 1 deletions

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arch/s390/include/asm/uaccess.h

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