linux-hardening - [PATCH 06/14] drm/amd/pm: Replace one-element array with flexible-array in struct phm_phase_shedding_limits

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Message-ID: <c3584841a052b031fe9dd963b5d6effe65aae640.1602020074.git.gustavoars@kernel.org>
Date:   Wed, 7 Oct 2020 11:06:14 -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 06/14] drm/amd/pm: Replace one-element array with
 flexible-array in struct phm_phase_shedding_limits_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_phase_shedding_limits_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
ptable->ucNumEntries by sizeof(struct phm_phase_shedding_limits_table)
when it should have multiplied it by sizeof(struct phm_phase_shedding_limits_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/5f7c5d36.6PStUZp2HRxAz7IM%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 | 12 ++++--------
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/amd/pm/inc/hwmgr.h b/drivers/gpu/drm/amd/pm/inc/hwmgr.h
index 361cb1125351..ad614e32079e 100644
--- a/drivers/gpu/drm/amd/pm/inc/hwmgr.h
+++ b/drivers/gpu/drm/amd/pm/inc/hwmgr.h
@@ -161,7 +161,7 @@ struct phm_vce_clock_voltage_dependency_record {
 
 struct phm_phase_shedding_limits_table {
 	uint32_t                           count;
-	struct phm_phase_shedding_limits_record  entries[1];
+	struct phm_phase_shedding_limits_record  entries[];
 };
 
 struct phm_vceclock_voltage_dependency_table {
diff --git a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
index a1b198045978..b2ef76580c6a 100644
--- a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
+++ b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c
@@ -1530,16 +1530,12 @@ static int init_phase_shedding_table(struct pp_hwmgr *hwmgr,
 				(((unsigned long)powerplay_table4) +
 				le16_to_cpu(powerplay_table4->usVddcPhaseShedLimitsTableOffset));
 			struct phm_phase_shedding_limits_table *table;
-			unsigned long size, i;
+			unsigned long i;
 
 
-			size = sizeof(unsigned long) +
-				(sizeof(struct phm_phase_shedding_limits_table) *
-				ptable->ucNumEntries);
-
-			table = kzalloc(size, GFP_KERNEL);
-
-			if (table == NULL)
+			table = kzalloc(struct_size(table, entries, ptable->ucNumEntries),
+					GFP_KERNEL);
+			if (!table)
 				return -ENOMEM;
 
 			table->count = (unsigned long)ptable->ucNumEntries;
-- 
2.27.0