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

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Date:   Fri, 29 Mar 2019 11:29:26 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Jann Horn <jannh@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.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: Re: [PATCH 1/2] kernel.h: use parentheses around argument in
 u64_to_user_ptr()


On 3/29/2019 2:53 AM, Jann Horn wrote:
> 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>


Looks good to me.
Reviewed-by: Mukesh Ojha <mojha@...eaurora.org>

-Mukesh

> ---
> 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);	\
>   }					\
>   )
>