[PATCH 6.19 822/844] drm/xe: Add bounds check on pat_index to prevent OOB kernel read in madvise

[Sasha Levin]

From: Jia Yao <jia.yao@xxxxxxxxx>

[ Upstream commit fbbe32618e97eff81577a01eb7d9adcd64a216d7 ]

When user provides a bogus pat_index value through the madvise IOCTL, the
xe_pat_index_get_coh_mode() function performs an array access without
validating bounds. This allows a malicious user to trigger an out-of-bounds
kernel read from the xe->pat.table array.

The vulnerability exists because the validation in madvise_args_are_sane()
directly calls xe_pat_index_get_coh_mode(xe, args->pat_index.val) without
first checking if pat_index is within [0, xe->pat.n_entries).

Although xe_pat_index_get_coh_mode() has a WARN_ON to catch this in debug
builds, it still performs the unsafe array access in production kernels.

v2(Matthew Auld)
- Using array_index_nospec() to mitigate spectre attacks when the value
is used

v3(Matthew Auld)
- Put the declarations at the start of the block

Fixes: ada7486c5668 ("drm/xe: Implement madvise ioctl for xe")
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v6.18+
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Shuicheng Lin <shuicheng.lin@xxxxxxxxx>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@xxxxxxxxx>
Cc: "Thomas Hellström" <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Signed-off-by: Jia Yao <jia.yao@xxxxxxxxx>
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Link: https://patch.msgid.link/20260205161529.1819276-1-jia.yao@xxxxxxxxx
(cherry picked from commit 944a3329b05510d55c69c2ef455136e2fc02de29)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/gpu/drm/xe/xe_vm_madvise.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
index cad3cf627c3f2..fe7e1b45f5c0c 100644
--- a/drivers/gpu/drm/xe/xe_vm_madvise.c
+++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
@@ -268,8 +268,13 @@ static bool madvise_args_are_sane(struct xe_device *xe, const struct drm_xe_madv
 		break;
 	case DRM_XE_MEM_RANGE_ATTR_PAT:
 	{
-		u16 coh_mode = xe_pat_index_get_coh_mode(xe, args->pat_index.val);
+		u16 pat_index, coh_mode;
 
+		if (XE_IOCTL_DBG(xe, args->pat_index.val >= xe->pat.n_entries))
+			return false;
+
+		pat_index = array_index_nospec(args->pat_index.val, xe->pat.n_entries);
+		coh_mode = xe_pat_index_get_coh_mode(xe, pat_index);
 		if (XE_IOCTL_DBG(xe, !coh_mode))
 			return false;
 
-- 
2.51.0