[PATCH] drm/i915: Fix potential spectre vulnerability

[Tvrtko Ursulin]

On 02/11/2023 10:16, chentao wrote:
> Fix smatch warning:
> drivers/gpu/drm/i915/gem/i915_gem_context.c:847 set_proto_ctx_sseu()
> warn: potential spectre issue 'pc->user_engines' [r] (local cap)
> 
> Signed-off-by: chentao <chentao at kylinos.cn>

I don't know if this is actually exploitable given the time deltas between the index is read from userspace and acted upon here, which is at least two ioctls apart. But I suppose no harm in fixing and for safety so we need to add:

Fixes: d4433c7600f7 ("drm/i915/gem: Use the proto-context to handle create parameters (v5)")
Cc: <stable at vger.kernel.org> # v5.15+

> ---
>   drivers/gpu/drm/i915/gem/i915_gem_context.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 9a9ff84c90d7..b2fdfc7ca4de 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -843,7 +843,7 @@ static int set_proto_ctx_sseu(struct drm_i915_file_private *fpriv,
>   
>   		if (idx >= pc->num_user_engines)
>   			return -EINVAL;
> -

Just please refrain from random whitespace modifications like this blank line removal. If you resend without that you can add my r-b.

Regards,

Tvrtko

> +		idx = array_index_nospec(idx, pc->num_user_engines);
>   		pe = &pc->user_engines[idx];
>   
>   		/* Only render engine supports RPCS configuration. */