This clarifies the comment above the access_ok check so a missing VERIFY_READ doesn't alarm anyone.
Signed-off-by: Kees Cook keescook@chromium.org Cc: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/gpu/drm/i915/i915_gem_execbuffer.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c index 2f2daeb..752e399 100644 --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c @@ -747,7 +747,11 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
length = exec[i].relocation_count * sizeof(struct drm_i915_gem_relocation_entry); - /* we may also need to update the presumed offsets */ + /* + * Validate memory range. Since we may need to update the + * presumed offsets, use VERIFY_WRITE. (Writable implies + * readable.) + */ if (!access_ok(VERIFY_WRITE, ptr, length)) return -EFAULT;
On Mon, Mar 11, 2013 at 12:26:30PM -0700, Kees Cook wrote:
This clarifies the comment above the access_ok check so a missing VERIFY_READ doesn't alarm anyone.
Do we really need to copy the interface documentation?
/** * access_ok: - Checks if a user space pointer is valid * @type: Type of access: %VERIFY_READ or %VERIFY_WRITE. Note that * %VERIFY_WRITE is a superset of %VERIFY_READ - if it is safe * to write to a block, it is always safe to read from it. * @addr: User space pointer to start of block to check * @size: Size of block to check */ -Chris
On Mon, Mar 11, 2013 at 1:51 PM, Chris Wilson chris@chris-wilson.co.uk wrote:
On Mon, Mar 11, 2013 at 12:26:30PM -0700, Kees Cook wrote:
This clarifies the comment above the access_ok check so a missing VERIFY_READ doesn't alarm anyone.
Do we really need to copy the interface documentation?
/**
- access_ok: - Checks if a user space pointer is valid
- @type: Type of access: %VERIFY_READ or %VERIFY_WRITE. Note that
%VERIFY_WRITE is a superset of %VERIFY_READ - if it is safeto write to a block, it is always safe to read from it.- @addr: User space pointer to start of block to check
- @size: Size of block to check
*/ -Chris
Probably not. It just seemed like the existing comment was insufficient after the removal of the redundant VERIFY_READ check that happened recently.
-Kees
On Mon, Mar 11, 2013 at 02:04:51PM -0700, Kees Cook wrote:
Probably not. It just seemed like the existing comment was insufficient after the removal of the redundant VERIFY_READ check that happened recently.
That's certainly true, the remaining comment is a little cryptic. Something more like:
/* We need to check that we can read the entire relocation array, but * as we may need to update the presumed_offsets upon execution, we * need to check now for full write access. */ -Chris
dri-devel@lists.freedesktop.org
-
Chris Wilson -
Kees Cook