Re: [Intel-gfx] [PATCH 3/4] drm/i915/selftest: Clear the output buffers before GPU writes

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 3/14/22 19:20, Ramalingam C wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
>
> When testing whether we can get the GPU to leak information about
> non-privileged state, we first need to ensure that the output buffer is
> set to a known value as the HW may opt to skip the write into memory for
> a non-privileged read of a sensitive register. We chose POISON_INUSE (0x5a)
> so that is both non-zero and distinct from the poison values used during
> the test.
>
> Reported-by: CQ Tang <cq.tang@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: CQ Tang <cq.tang@intel.com>
> cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>



> ---
>   drivers/gpu/drm/i915/gt/selftest_lrc.c | 32 ++++++++++++++++++++++----
>   1 file changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index 0a8ed4246082..b9cc89de01bf 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -1346,6 +1346,30 @@ static int compare_isolation(struct intel_engine_cs *engine,
>   	return err;
>   }
>   
> +static struct i915_vma *
> +create_result_vma(struct i915_address_space *vm, unsigned long sz)
> +{
> +	struct i915_vma *vma;
> +	void *ptr;
> +
> +	vma = create_user_vma(vm, sz);
> +	if (IS_ERR(vma))
> +		return vma;
> +
> +	/* Set the results to a known value distinct from the poison */
> +	ptr = i915_gem_object_pin_map(vma->obj, I915_MAP_WC);
> +	if (IS_ERR(ptr)) {
> +		i915_vma_put(vma);
> +		return ERR_CAST(ptr);
> +	}
> +
> +	memset(ptr, POISON_INUSE, vma->size);
> +	i915_gem_object_flush_map(vma->obj);
> +	i915_gem_object_unpin_map(vma->obj);
> +
> +	return vma;
> +}
> +
>   static int __lrc_isolation(struct intel_engine_cs *engine, u32 poison)
>   {
>   	u32 *sema = memset32(engine->status_page.addr + 1000, 0, 1);
> @@ -1364,13 +1388,13 @@ static int __lrc_isolation(struct intel_engine_cs *engine, u32 poison)
>   		goto err_A;
>   	}
>   
> -	ref[0] = create_user_vma(A->vm, SZ_64K);
> +	ref[0] = create_result_vma(A->vm, SZ_64K);
>   	if (IS_ERR(ref[0])) {
>   		err = PTR_ERR(ref[0]);
>   		goto err_B;
>   	}
>   
> -	ref[1] = create_user_vma(A->vm, SZ_64K);
> +	ref[1] = create_result_vma(A->vm, SZ_64K);
>   	if (IS_ERR(ref[1])) {
>   		err = PTR_ERR(ref[1]);
>   		goto err_ref0;
> @@ -1392,13 +1416,13 @@ static int __lrc_isolation(struct intel_engine_cs *engine, u32 poison)
>   	}
>   	i915_request_put(rq);
>   
> -	result[0] = create_user_vma(A->vm, SZ_64K);
> +	result[0] = create_result_vma(A->vm, SZ_64K);
>   	if (IS_ERR(result[0])) {
>   		err = PTR_ERR(result[0]);
>   		goto err_ref1;
>   	}
>   
> -	result[1] = create_user_vma(A->vm, SZ_64K);
> +	result[1] = create_result_vma(A->vm, SZ_64K);
>   	if (IS_ERR(result[1])) {
>   		err = PTR_ERR(result[1]);
>   		goto err_result0;