linux-kernel - Re: [PATCH RESEND 3/4] drm/i915/gem: Replace user_access_begin by user_write_access

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Date:   Thu, 2 Apr 2020 00:52:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, airlied@...ux.ie,
        daniel@...ll.ch, torvalds@...ux-foundation.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, hpa@...or.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH RESEND 3/4] drm/i915/gem: Replace user_access_begin by
 user_write_access_begin

On Thu, Apr 02, 2020 at 07:34:18AM +0000, Christophe Leroy wrote:
> When i915_gem_execbuffer2_ioctl() is using user_access_begin(),
> that's only to perform unsafe_put_user() so use
> user_write_access_begin() in order to only open write access.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Why is this split from the other conversions?

Reviewed-by: Kees Cook <keescook@...omium.org>


> ---
>  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 7643a30ba4cd..4be8205a70b6 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1611,14 +1611,14 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
>  		 * happened we would make the mistake of assuming that the
>  		 * relocations were valid.
>  		 */
> -		if (!user_access_begin(urelocs, size))
> +		if (!user_write_access_begin(urelocs, size))
>  			goto end;
>  
>  		for (copied = 0; copied < nreloc; copied++)
>  			unsafe_put_user(-1,
>  					&urelocs[copied].presumed_offset,
>  					end_user);
> -		user_access_end();
> +		user_write_access_end();
>  
>  		eb->exec[i].relocs_ptr = (uintptr_t)relocs;
>  	}
> @@ -1626,7 +1626,7 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
>  	return 0;
>  
>  end_user:
> -	user_access_end();
> +	user_write_access_end();
>  end:
>  	kvfree(relocs);
>  	err = -EFAULT;
> @@ -2991,7 +2991,8 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
>  		 * And this range already got effectively checked earlier
>  		 * when we did the "copy_from_user()" above.
>  		 */
> -		if (!user_access_begin(user_exec_list, count * sizeof(*user_exec_list)))
> +		if (!user_write_access_begin(user_exec_list,
> +					     count * sizeof(*user_exec_list)))
>  			goto end;
>  
>  		for (i = 0; i < args->buffer_count; i++) {
> @@ -3005,7 +3006,7 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
>  					end_user);
>  		}
>  end_user:
> -		user_access_end();
> +		user_write_access_end();
>  end:;
>  	}
>  
> -- 
> 2.25.0
> 

-- 
Kees Cook