linux-kernel - [PATCH 1/2] kernel.h: use parentheses around argument in u64_to_user

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Message-Id: <20190328212321.92463-1-jannh@google.com>
Date:   Thu, 28 Mar 2019 22:23:20 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, jannh@...gle.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Signed-off-by : Qiaowei Ren" <qiaowei.ren@...el.com>
Subject: [PATCH 1/2] kernel.h: use parentheses around argument in u64_to_user_ptr()

Use parentheses around uses of the argument in u64_to_user_ptr() to ensure
that the cast doesn't apply to part of the argument.

There are existing uses of the macro of the form `u64_to_user_ptr(A + B)`,
which expands to `(void __user *)(uintptr_t)A + B` (the cast applies to the
first operand of the addition, the addition is a pointer addition). This
happens to still work as intended, the semantic difference doesn't cause a
difference in behavior.
But I want to use u64_to_user_ptr() with a ternary operator in the
argument, like so: `u64_to_user_ptr(A ? B : C)`. This currently doesn't
work as intended.

Fixes: f09174c501f8 ("x86: add user_atomic_cmpxchg_inatomic at uaccess.h")
Signed-off-by: Jann Horn <jannh@...gle.com>
---
Can we take this patch through the x86 tree with the following one, or
do we need to get this one through akpm's tree first?

 include/linux/kernel.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 34a5036debd3..2d14e21c16c0 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -47,8 +47,8 @@

 #define u64_to_user_ptr(x) (		\
 {					\
-	typecheck(u64, x);		\
-	(void __user *)(uintptr_t)x;	\
+	typecheck(u64, (x));		\
+	(void __user *)(uintptr_t)(x);	\
 }					\
 )

-- 
2.21.0.392.gf8f6787159e-goog