[PATCH 6.12.y] drm/i915/dmc: Harden DMC firmware payload parsing

[Sasha Levin <sashal@kernel.org>]

From: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>

[ Upstream commit 8bb1858db453cd4250e3b633f5d2d09206024ca6 ]

Validate the conversion of the DMC firmware size from dwords to bytes
using check_mul_overflow() before calculating the firmware payload size.

Reject zero-length payloads and zero MMIO counts in the DMC firmware
header so malformed firmware is caught early. Also set dmc_fw_size only
after the payload allocation succeeds.

Fixes: eb805623d8b1 ("drm/i915/skl: Add support to load SKL CSR firmware.")
Cc: stable@vger.kernel.org
Assisted-by: Claude-Code:Sonnet-5
Signed-off-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian@intel.com>
Reviewed-by: Mitul Golani<mitulkumar.ajitkumar.golani@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patch.msgid.link/20260922133535.3180973-5-dibin.moolakadan.subrahmanian@intel.com
(cherry picked from commit efde6601a1f1daedfe3dcc2816c934ddb44e3eef)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
[ sashal: Changed logging arguments from `display->drm` to `&i915->drm`. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/i915/display/intel_dmc.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
index 7c756d5ba2a22..641dabf275e73 100644
--- a/drivers/gpu/drm/i915/display/intel_dmc.c
+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
@@ -796,7 +796,7 @@ static u32 parse_dmc_fw_header(struct intel_dmc *dmc,
 	}
 
 	/* Cache the dmc header info. */
-	if (mmio_count > mmio_count_max) {
+	if (!mmio_count || mmio_count > mmio_count_max) {
 		drm_err(&i915->drm, "DMC firmware has wrong mmio count %u\n", mmio_count);
 		return 0;
 	}
@@ -819,13 +819,21 @@ static u32 parse_dmc_fw_header(struct intel_dmc *dmc,
 			    disable_dmc_evt(i915, dmc_id, dmc_info->mmioaddr[i],
 					    dmc_info->mmiodata[i]) ? " (disabling)" : "");
 	}
-	dmc_info->mmio_count = mmio_count;
-	dmc_info->start_mmioaddr = start_mmioaddr;
 
 	rem_size -= header_len_bytes;
 
 	/* fw_size is in dwords, so multiplied by 4 to convert into bytes. */
-	payload_size = dmc_header->fw_size * 4;
+	if (check_mul_overflow(dmc_header->fw_size, 4u, &payload_size)) {
+		drm_err(&i915->drm, "DMC fw_size too large (%u dwords)\n",
+			dmc_header->fw_size);
+		return 0;
+	}
+
+	if (!payload_size) {
+		drm_err(&i915->drm, "DMC firmware has empty payload\n");
+		return 0;
+	}
+
 	if (rem_size < payload_size)
 		goto error_truncated;
 
@@ -833,12 +841,15 @@ static u32 parse_dmc_fw_header(struct intel_dmc *dmc,
 		drm_err(&i915->drm, "DMC FW too big (%u bytes)\n", payload_size);
 		return 0;
 	}
-	dmc_info->dmc_fw_size = dmc_header->fw_size;
 
 	dmc_info->payload = kmalloc(payload_size, GFP_KERNEL);
 	if (!dmc_info->payload)
 		return 0;
 
+	dmc_info->mmio_count = mmio_count;
+	dmc_info->start_mmioaddr = start_mmioaddr;
+	dmc_info->dmc_fw_size = dmc_header->fw_size;
+
 	payload = (u8 *)(dmc_header) + header_len_bytes;
 	memcpy(dmc_info->payload, payload, payload_size);
 
-- 
2.53.0