linux-kernel - Re: [PATCH] x86/uaccess: instrument copy_from_user

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Message-ID: <Y1j+Tt9mnMDU0zO+@hirez.programming.kicks-ass.net>
Date:   Wed, 26 Oct 2022 11:30:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org
Subject: Re: [PATCH] x86/uaccess: instrument copy_from_user_nmi()

On Wed, Oct 26, 2022 at 12:17:55AM +0200, Alexander Potapenko wrote:
> Make sure usercopy hooks from linux/instrumented.h are invoked for
> copy_from_user_nmi().
> This fixes KMSAN false positives reported when dumping opcodes for a
> stack trace.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: x86@...nel.org
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
>  arch/x86/lib/usercopy.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
> index f1bb186171562..24b48af274173 100644
> --- a/arch/x86/lib/usercopy.c
> +++ b/arch/x86/lib/usercopy.c
> @@ -6,6 +6,7 @@
>  
>  #include <linux/uaccess.h>
>  #include <linux/export.h>
> +#include <linux/instrumented.h>
>  
>  #include <asm/tlbflush.h>
>  
> @@ -44,7 +45,9 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
>  	 * called from other contexts.
>  	 */
>  	pagefault_disable();
> +	instrument_copy_from_user_before(to, from, n);
>  	ret = raw_copy_from_user(to, from, n);
> +	instrument_copy_from_user_after(to, from, n, ret);
>  	pagefault_enable();
>  
>  	return ret;

Is all that instrumentation NMI safe? ISTR having seen locks in some of
that *SAN stuff.

Also did this want:

Fixes: 59298997df89 ("x86/uaccess: avoid check_object_size() in copy_from_user_nmi()")

?