linux-kernel - [PATCH 09/14] drm/amd/pm: Replace one-element array with flexible-array in struct phm_samu_clock_voltage_dependency

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Message-ID: <7aa857a6242477b90da3643678d2798c7037b30f.1602020074.git.gustavoars@kernel.org>
Date:   Wed, 7 Oct 2020 11:08:08 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-hardening@...r.kernel.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH 09/14] drm/amd/pm: Replace one-element array with
 flexible-array in struct phm_samu_clock_voltage_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].

Refactor the code according to the use of a flexible-array member in
struct phm_samu_clock_voltage_dependency_table, instead of a one-element array,
and use the struct_size() helper to calculate the size for the allocation.

Also, save some heap space as the original code is multiplying
table->numEntries by sizeof(struct phm_samu_clock_voltage_dependency_table)
when it should have been multiplied it by
sizeof(struct phm_samu_clock_voltage_dependency_record) instead.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays

Build-tested-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/5f7c5d3a.ryM4GmZr3e0JeZy+%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/gpu/drm/amd/pm/inc/hwmgr.h                    |  2 +-
 .../gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c  | 11 ++++-------
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/amd/pm/inc/hwmgr.h b/drivers/gpu/drm/amd/pm/inc/hwmgr.h
index 7e0c948a7097..dad703ba0522 100644
--- a/drivers/gpu/drm/amd/pm/inc/hwmgr.h
+++ b/drivers/gpu/drm/amd/pm/inc/hwmgr.h
@@ -404,7 +404,7 @@ struct phm_samu_clock_voltage_dependency_record {
 
 struct phm_samu_clock_voltage_dependency_table {
 	uint8_t count;
-	struct phm_samu_clock_voltage_dependency_record entries[1];
+	struct phm_samu_clock_voltage_dependency_record entries[];
 };
 
 struct phm_cac_tdp_table {
diff --git a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
index e059802d1e25..48d550d26c6a 100644
--- a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
+++ b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
@@ -1163,15 +1163,12 @@ static int get_samu_clock_voltage_limit_table(struct pp_hwmgr *hwmgr,
 		 struct phm_samu_clock_voltage_dependency_table **ptable,
 		 const ATOM_PPLIB_SAMClk_Voltage_Limit_Table *table)
 {
-	unsigned long table_size, i;
+	unsigned long i;
 	struct phm_samu_clock_voltage_dependency_table *samu_table;
 
-	table_size = sizeof(unsigned long) +
-		sizeof(struct phm_samu_clock_voltage_dependency_table) *
-		table->numEntries;
-
-	samu_table = kzalloc(table_size, GFP_KERNEL);
-	if (NULL == samu_table)
+	samu_table = kzalloc(struct_size(samu_table, entries, table->numEntries),
+			     GFP_KERNEL);
+	if (!samu_table)
 		return -ENOMEM;
 
 	samu_table->count = table->numEntries;
-- 
2.27.0