From: Will Deacon <will.deacon@arm.com>

Date: Wed, 10 Apr 2019 11:49:11 +0100

Subject: arm64: futex: Avoid copying out uninitialised stack in failed

 cmpxchg()

Git-commit: 8e4e0ac02b449297b86498ac24db5786ddd9f647

Patch-mainline: v5.2-rc1

References: git-fixes

Returning an error code from futex_atomic_cmpxchg_inatomic() indicates

that the caller should not make any use of *uval, and should instead act

upon on the value of the error code. Although this is implemented

correctly in our futex code, we needlessly copy uninitialised stack to

*uval in the error case, which can easily be avoided.

Signed-off-by: Will Deacon <will.deacon@arm.com>

Acked-by: Ivan T. Ivanov <iivanov@suse.de>

---

 arch/arm64/include/asm/futex.h |    4 +++-

 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/futex.h

+++ b/arch/arm64/include/asm/futex.h

@@ -134,7 +134,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval,

 	: "memory");

 	uaccess_disable();

-	*uval = val;

+	if (!ret)

+		*uval = val;

+

 	return ret;

 }