From: Will Deacon <will.deacon@arm.com>
Date: Wed, 10 Apr 2019 10:49:11 +0000 (+0100)
Subject: arm64: futex: Avoid copying out uninitialised stack in failed cmpxchg()
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=8e4e0ac02b449297b86498ac24db5786ddd9f647;p=openwrt%2Fstaging%2Fblogic.git

arm64: futex: Avoid copying out uninitialised stack in failed cmpxchg()

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>
---

diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 2d78ea6932b7..bdb3c05070a2 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -134,7 +134,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *_uaddr,
 	: "memory");
 	uaccess_disable();
 
-	*uval = val;
+	if (!ret)
+		*uval = val;
+
 	return ret;
 }