Re: [PATCH v18 10/15] drm/radeon: untag user pointers in radeon_gem_userptr_ioctl

[Kees Cook <keescook@chromium.org>]

On Mon, Jun 24, 2019 at 04:32:55PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends kernel ABI to allow to pass
> tagged user pointers (with the top byte set to something else other than
> 0x00) as syscall arguments.
> 
> In radeon_gem_userptr_ioctl() an MMU notifier is set up with a (tagged)
> userspace pointer. The untagged address should be used so that MMU
> notifiers for the untagged address get correctly matched up with the right
> BO. This funcation also calls radeon_ttm_tt_pin_userptr(), which uses
> provided user pointers for vma lookups, which can only by done with
> untagged pointers.
> 
> This patch untags user pointers in radeon_gem_userptr_ioctl().
> 
> Suggested-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

-Kees

> ---
>  drivers/gpu/drm/radeon/radeon_gem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
> index 44617dec8183..90eb78fb5eb2 100644
> --- a/drivers/gpu/drm/radeon/radeon_gem.c
> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> @@ -291,6 +291,8 @@ int radeon_gem_userptr_ioctl(struct drm_device *dev, void *data,
>  	uint32_t handle;
>  	int r;
>  
> +	args->addr = untagged_addr(args->addr);
> +
>  	if (offset_in_page(args->addr | args->size))
>  		return -EINVAL;
>  
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook