From ef6c3af96ee190927aa285c4dc187af765821d13 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Sat, 7 Dec 2019 22:26:44 +0000
Subject: drm/i915/gem: Comment on inability to check args.pad for MMAP_OFFSET
Git-commit: 8d65859a4cbae92f441b9aec8780055a361cc3d0
Patch-mainline: v5.6-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322
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
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/i915/gem/i915_gem_mman.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index 3a3f30bc8ac7..879fff8adc48 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -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)
--
2.28.0