linux-kernel - Re: [PATCH v3 2/3] x86: Use static_cpu_has in uaccess region to avoid instrumentation

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Date:   Thu, 13 Jun 2019 11:21:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     aryabinin@...tuozzo.com, dvyukov@...gle.com, glider@...gle.com,
        andreyknvl@...gle.com, mark.rutland@....com, hpa@...or.com,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        x86@...nel.org, arnd@...db.de, jpoimboe@...hat.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 2/3] x86: Use static_cpu_has in uaccess region to
 avoid instrumentation

On Fri, May 31, 2019 at 05:08:30PM +0200, Marco Elver wrote:
> This patch is a pre-requisite for enabling KASAN bitops instrumentation;
> using static_cpu_has instead of boot_cpu_has avoids instrumentation of
> test_bit inside the uaccess region. With instrumentation, the KASAN
> check would otherwise be flagged by objtool.
> 
> For consistency, kernel/signal.c was changed to mirror this change,
> however, is never instrumented with KASAN (currently unsupported under
> x86 32bit).

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Thanks!

> 
> Signed-off-by: Marco Elver <elver@...gle.com>
> Suggested-by: H. Peter Anvin <hpa@...or.com>
> ---
> Changes in v3:
> * Use static_cpu_has instead of moving boot_cpu_has outside uaccess
>   region.
> 
> Changes in v2:
> * Replaces patch: 'tools/objtool: add kasan_check_* to uaccess
>   whitelist'
> ---
>  arch/x86/ia32/ia32_signal.c | 2 +-
>  arch/x86/kernel/signal.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
> index 629d1ee05599..1cee10091b9f 100644
> --- a/arch/x86/ia32/ia32_signal.c
> +++ b/arch/x86/ia32/ia32_signal.c
> @@ -358,7 +358,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
>  		put_user_ex(ptr_to_compat(&frame->uc), &frame->puc);
>  
>  		/* Create the ucontext.  */
> -		if (boot_cpu_has(X86_FEATURE_XSAVE))
> +		if (static_cpu_has(X86_FEATURE_XSAVE))
>  			put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
>  		else
>  			put_user_ex(0, &frame->uc.uc_flags);
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index 364813cea647..52eb1d551aed 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -391,7 +391,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
>  		put_user_ex(&frame->uc, &frame->puc);
>  
>  		/* Create the ucontext.  */
> -		if (boot_cpu_has(X86_FEATURE_XSAVE))
> +		if (static_cpu_has(X86_FEATURE_XSAVE))
>  			put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
>  		else
>  			put_user_ex(0, &frame->uc.uc_flags);
> -- 
> 2.22.0.rc1.257.g3120a18244-goog
>