[PATCH] drm/amd/pm: bound SCLK FCW range entries to the table size

[Hari Mishal <harimishal1@gmail.com>]

atomctrl_get_smc_sclk_range_table() copies ucSclkEntryNum entries from
the VBIOS SMU_Info table into pp_atom_ctrl_sclk_range_table. Both the
source (asSclkFcwRangeEntry[]) and destination (table->entry[]) arrays
are fixed at MAX_SCLK_RANGE (8) entries, but ucSclkEntryNum is an
unchecked u8 read straight from the VBIOS, so it can be up to 255. The
destination is stack-allocated in both callers
(polaris10_get_sclk_range_table(), vegam_get_sclk_range_table()), so a
count above 8 overflows a stack buffer, not just a heap read.

Reject counts above MAX_SCLK_RANGE rather than clamping to it. Only
one version of this VBIOS struct (ATOM_SMU_INFO_V2_1) has ever
existed, so a count above 8 corresponds to no legitimate table format
and means either a corrupted or a tampered VBIOS.

Fixes: a23eefa2f461 ("drm/amd/powerplay: enable dpm for baffin.")
Assisted-by: gkh_clanker_t1000
Signed-off-by: Hari Mishal <harimishal1@gmail.com>
---
 drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c
index 4b796d60b03d..3217ad3c1d17 100644
--- a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c
+++ b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/ppatomctrl.c
@@ -1025,6 +1025,9 @@ int atomctrl_get_smc_sclk_range_table(struct pp_hwmgr *hwmgr, struct pp_atom_ctr
 	if (!psmu_info)
 		return -EINVAL;
 
+	if (psmu_info->ucSclkEntryNum > MAX_SCLK_RANGE)
+		return -EINVAL;
+
 	for (i = 0; i < psmu_info->ucSclkEntryNum; i++) {
 		table->entry[i].ucVco_setting = psmu_info->asSclkFcwRangeEntry[i].ucVco_setting;
 		table->entry[i].ucPostdiv = psmu_info->asSclkFcwRangeEntry[i].ucPostdiv;
-- 
2.43.0