Re: [PATCH v2] drm/i915: Fix a VMA UAF for multi-gt platform

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

On 06.06.2023 22:27, Nirmoy Das wrote:
> Ensure correct handling of closed VMAs on multi-gt platforms to prevent
> Use-After-Free. Currently, when GT0 goes idle, closed VMAs that are
> exclusively added to GT0's closed_vma link (gt->closed_vma) and
> subsequently freed by i915_vma_parked(), which assumes the entire GPU is
> idle. However, on platforms with multiple GTs, such as MTL, GT1 may
> remain active while GT0 is idle. This causes GT0 to mistakenly consider
> the closed VMAs in its closed_vma list as unnecessary, potentially
> leading to Use-After-Free issues if a job for GT1 attempts to access a
> freed VMA.
>
> Although we do take a wakeref for GT0 but it happens later, after
> evaluating VMAs. To mitigate this, it is necessary to hold a GT0 wakeref
> early.
>
> v2: Use gt id to detect multi-tile(Andi)
>      Fix the incorrect error path.
>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Cc: Chris Wilson <chris.p.wilson@xxxxxxxxx>
> Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> Cc: Sushma Venkatesh Reddy <sushma.venkatesh.reddy@xxxxxxxxx>
> Tested-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 3aeede6aee4d..c2a67435acfa 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -2683,6 +2683,7 @@ static int
>   eb_select_engine(struct i915_execbuffer *eb)
>   {
>   	struct intel_context *ce, *child;
> +	struct intel_gt *gt;
>   	unsigned int idx;
>   	int err;
>   
> @@ -2706,10 +2707,16 @@ eb_select_engine(struct i915_execbuffer *eb)
>   		}
>   	}
>   	eb->num_batches = ce->parallel.number_children + 1;
> +	gt = ce->engine->gt;
>   
>   	for_each_child(ce, child)
>   		intel_context_get(child);
>   	intel_gt_pm_get(ce->engine->gt);

intel_gt_pm_get(gt)


> +	/* Keep GT0 active on MTL so that i915_vma_parked() doesn't
> +	 * free VMAs while execbuf ioctl is validating VMAs.
> +	 */
> +	if (gt->info.id)
> +		intel_gt_pm_get(to_gt(gt->i915));
>   
>   	if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
>   		err = intel_context_alloc_state(ce);
> @@ -2748,6 +2755,9 @@ eb_select_engine(struct i915_execbuffer *eb)
>   	return err;
>   
>   err:
> +	if (gt->info.id)
> +		intel_gt_pm_put(to_gt(gt->i915));
> +
>   	intel_gt_pm_put(ce->engine->gt);

intel_gt_pm_put(gt)


Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>

Regards
Andrzej

>   	for_each_child(ce, child)
>   		intel_context_put(child);
> @@ -2761,6 +2771,8 @@ eb_put_engine(struct i915_execbuffer *eb)
>   	struct intel_context *child;
>   
>   	i915_vm_put(eb->context->vm);
> +	if (eb->gt->info.id)
> +		intel_gt_pm_put(to_gt(eb->gt->i915));
>   	intel_gt_pm_put(eb->gt);
>   	for_each_child(eb->context, child)
>   		intel_context_put(child);