linux-kernel - [PATCH] drm/amd/display: Use kmalloc

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Message-ID: <20250913052109.2638-1-bold.zone2373@fastmail.com>
Date: Fri, 12 Sep 2025 22:19:52 -0700
From: James Flowers <bold.zone2373@...tmail.com>
To: harry.wentland@....com,
	sunpeng.li@....com,
	siqueira@...lia.com,
	alexander.deucher@....com,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	roman.li@....com,
	alvin.lee2@....com,
	skhan@...uxfoundation.org
Cc: James Flowers <bold.zone2373@...tmail.com>,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev
Subject: [PATCH] drm/amd/display: Use kmalloc_array() instead of kmalloc()

Documentation/process/deprecated.rst recommends against the use of kmalloc
with dynamic size calculations due to the risk of overflow and smaller
allocation being made than the caller was expecting. This could lead to
buffer overflow in code similar to the memcpy in
amdgpu_dm_plane_add_modifier().

Signed-off-by: James Flowers <bold.zone2373@...tmail.com>
---
I see that in amdgpu_dm_plane_get_plane_modifiers, capacity is initialized to 
only 128, but it is probably preferable to refactor.
 
Tested on a Steam Deck OLED with no apparent regressions using these test suites from
igt-gpu-tools: 
1) kms_plane
2) amd_plane
3) amd_fuzzing
4) testdisplay 

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
index b7c6e8d13435..b587d2033f0b 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
@@ -146,7 +146,7 @@ static void amdgpu_dm_plane_add_modifier(uint64_t **mods, uint64_t *size, uint64
 
 	if (*cap - *size < 1) {
 		uint64_t new_cap = *cap * 2;
-		uint64_t *new_mods = kmalloc(new_cap * sizeof(uint64_t), GFP_KERNEL);
+		uint64_t *new_mods = kmalloc_array(new_cap, sizeof(uint64_t), GFP_KERNEL);
 
 		if (!new_mods) {
 			kfree(*mods);
@@ -732,7 +732,7 @@ static int amdgpu_dm_plane_get_plane_modifiers(struct amdgpu_device *adev, unsig
 	if (adev->family < AMDGPU_FAMILY_AI)
 		return 0;
 
-	*mods = kmalloc(capacity * sizeof(uint64_t), GFP_KERNEL);
+	*mods = kmalloc_array(capacity, sizeof(uint64_t), GFP_KERNEL);
 
 	if (plane_type == DRM_PLANE_TYPE_CURSOR) {
 		amdgpu_dm_plane_add_modifier(mods, &size, &capacity, DRM_FORMAT_MOD_LINEAR);
-- 
2.51.0