linux-hardening - [PATCH][next] drm/amd/pm: Replace one-element array with flexible-array in struct _ATOM_Vega10_GFXCLK_Dependency

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Date:   Wed, 10 Feb 2021 17:26:00 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Evan Quan <evan.quan@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] drm/amd/pm: Replace one-element array with
 flexible-array in struct _ATOM_Vega10_GFXCLK_Dependency_Table

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Use flexible-array member in struct _ATOM_Vega10_GFXCLK_Dependency_Table,
instead of one-element array.

Also, this helps with the ongoing efforts to enable -Warray-bounds and
fix the following warning:

drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega10_hwmgr.c: In function ‘vega10_get_pp_table_entry_callback_func’:
drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega10_hwmgr.c:3113:30: warning: array subscript 4 is above array bounds of ‘ATOM_Vega10_GFXCLK_Dependency_Record[1]’ {aka ‘struct _ATOM_Vega10_GFXCLK_Dependency_Record[1]’} [-Warray-bounds]
 3113 |     gfxclk_dep_table->entries[4].ulClk;
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Build-tested-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/6023ff3d.WY3sSCkGRQPdPlVo%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_pptable.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_pptable.h b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_pptable.h
index c934e9612c1b..9c479bd9a786 100644
--- a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_pptable.h
+++ b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_pptable.h
@@ -161,9 +161,9 @@ typedef struct _ATOM_Vega10_MCLK_Dependency_Record {
 } ATOM_Vega10_MCLK_Dependency_Record;
 
 typedef struct _ATOM_Vega10_GFXCLK_Dependency_Table {
-    UCHAR ucRevId;
-    UCHAR ucNumEntries;                                         /* Number of entries. */
-    ATOM_Vega10_GFXCLK_Dependency_Record entries[1];            /* Dynamically allocate entries. */
+	UCHAR ucRevId;
+	UCHAR ucNumEntries;					/* Number of entries. */
+	ATOM_Vega10_GFXCLK_Dependency_Record entries[];		/* Dynamically allocate entries. */
 } ATOM_Vega10_GFXCLK_Dependency_Table;
 
 typedef struct _ATOM_Vega10_MCLK_Dependency_Table {
-- 
2.27.0