[igt-dev] [PATCH] kms_prop_blob: Add new subtest for write-only blobs

[Petri Latvala]

On Wed, May 25, 2022 at 03:18:01PM -0400, Mark Yacoub wrote:
> [Why]
> Some blobs support secret data injected into the kernel that should be
> retrieved back to user space (like HDCP key provisioned from a server
> and injected to the kernel)
> 
> [How]
> Create a blob using the write only flag and validate that the data it
> holds can't be read again by the user space.
> Compare this behavior against a blob created without the flag.
> 
> TEST=blob-write-only
> TESTED-ON=Trogdor
> 
> Signed-off-by: Mark Yacoub <markyacoub at chromium.org>
> ---
>  include/drm-uapi/drm_mode.h |  6 ++++++
>  tests/kms_prop_blob.c       | 39 +++++++++++++++++++++++++++++++++++--
>  2 files changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/include/drm-uapi/drm_mode.h b/include/drm-uapi/drm_mode.h
> index e4a2570a..38d6c1f0 100644
> --- a/include/drm-uapi/drm_mode.h
> +++ b/include/drm-uapi/drm_mode.h
> @@ -1075,6 +1075,9 @@ struct drm_format_modifier {
>  	__u64 modifier;
>  };
>  
> +#define DRM_MODE_CREATE_BLOB_WRITE_ONLY                                        \
> +       (1 << 0) /* data of the blob can't be read by user space */
> +
>  /**
>   * struct drm_mode_create_blob - Create New blob property
>   *
> @@ -1088,6 +1091,9 @@ struct drm_mode_create_blob {
>  	__u32 length;
>  	/** @blob_id: Return: new property ID. */
>  	__u32 blob_id;
> +	/** Flags for special handling. */
> +       __u32 flags;
> +       __u32 pad;
>  };
>  
>  /**

Have the changes to drm-uapi in a separate commit and state which
kernel sha they're copied from. And actually copy, no hand editing.


> diff --git a/tests/kms_prop_blob.c b/tests/kms_prop_blob.c
> index 96aa6d8d..c130a432 100644
> --- a/tests/kms_prop_blob.c
> +++ b/tests/kms_prop_blob.c
> @@ -75,6 +75,7 @@ validate_prop(int fd, uint32_t prop_id)
>  {
>  	struct drm_mode_get_blob get;
>  	struct drm_mode_modeinfo ret_mode;
> +	ret_mode.clock = 0;
>  
>  	get.blob_id = prop_id;
>  	get.length = 0;
> @@ -94,12 +95,13 @@ validate_prop(int fd, uint32_t prop_id)
>  }
>  
>  static uint32_t
> -create_prop(int fd)
> +create_prop_with_flags(int fd, uint32_t flags)
>  {
>  	struct drm_mode_create_blob create;
>  
>  	create.length = sizeof(test_mode_valid);
> -	create.data = (uintptr_t) &test_mode_valid;
> +	create.data = (uintptr_t)&test_mode_valid;
> +	create.flags = flags;
>  
>  	do_ioctl(fd, DRM_IOCTL_MODE_CREATEPROPBLOB, &create);

How does this behave if the running kernel doesn't have flags support
at all? Is that discoverable from userspace somehow?


-- 
Petri Latvala



>  	igt_assert_neq_u32(create.blob_id, 0);
> @@ -107,6 +109,12 @@ create_prop(int fd)
>  	return create.blob_id;
>  }
>  
> +static uint32_t
> +create_prop(int fd)
> +{
> +	return create_prop_with_flags(fd, 0);
> +}
> +
>  static int
>  destroy_prop(int fd, uint32_t prop_id)
>  {
> @@ -223,6 +231,29 @@ test_multiple(int fd)
>  		igt_assert_eq(validate_prop(fd, prop_ids[i]), ENOENT);
>  }
>  
> +/* Create 2 blobs, a write-only and a read-write blob.
> +   The only difference is the flag.
> +   Check that we can't read the value of the blob with the write-only flag.
> +*/
> +static void
> +test_write_only(int fd) {
> +	uint32_t rw_blob_id, wo_blob_id;
> +	int wo_ret = 0;
> +
> +	rw_blob_id = create_prop_with_flags(fd, 0);
> +	wo_blob_id = create_prop_with_flags(fd, DRM_MODE_CREATE_BLOB_WRITE_ONLY);
> +
> +	igt_assert_eq(validate_prop(fd, rw_blob_id), 0);
> +
> +	wo_ret = validate_prop(fd, wo_blob_id);
> +	/* The correct length should be copied to the length field. */
> +	igt_assert_neq(wo_ret, ENOMEM);
> +	igt_assert_eq(wo_ret, EINVAL);
> +
> +	igt_assert_eq(destroy_prop(fd, rw_blob_id), 0);
> +	igt_assert_eq(destroy_prop(fd, wo_blob_id), 0);
> +}
> +
>  static void
>  test_core(int fd)
>  {
> @@ -335,6 +366,10 @@ igt_main
>  	igt_subtest("blob-multiple")
>  		test_multiple(fd);
>  
> +	igt_describe("Test validates Write-only blobs can't be read back by user space.");
> +	igt_subtest("blob-write-only")
> +		test_write_only(fd);
> +
>  	prop_tests(fd);
>  
>  	igt_fixture
> -- 
> 2.36.1.124.g0e6072fb45-goog
>