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drm/i915/gem: Comment on inability to check args.pad for MMAP_OFFSET

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Since we didn't check and insist that args.pad must be zero for MMAP_GTT
historically, we cannot insert a check now as old userspace may be
feeding in garbage. As such the lack of check is enshrined into the ABI,
so add a comment to remind us we cannot add the check later.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191207222644.2830129-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2019-12-07 22:26:44 +00:00
parent d634110007
commit 8d65859a4c
1 changed files with 9 additions and 0 deletions
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9
drivers/gpu/drm/i915/gem/i915_gem_mman.c
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@ -620,6 +620,15 @@ i915_gem_mmap_offset_ioctl(struct drm_device *dev, void *data,
enum i915_mmap_type type;
int err;
/*
* Historically we failed to check args.pad and args.offset
* and so we cannot use those fields for user input and we cannot
* add -EINVAL for them as the ABI is fixed, i.e. old userspace
* may be feeding in garbage in those fields.
*
* if (args->pad) return -EINVAL; is verbotten!
*/
err = i915_user_extensions(u64_to_user_ptr(args->extensions),
NULL, 0, NULL);
if (err)