[coreboot-gerrit] Change in coreboot[master]: device/dram/ddr4: Check spd_bytes_total and spd_bytes_used values

[Nico Huber (Code Review)]

Nico Huber has submitted this change. ( https://review.coreboot.org/c/coreboot/+/35558 )

Change subject: device/dram/ddr4: Check spd_bytes_total and spd_bytes_used values
......................................................................

device/dram/ddr4: Check spd_bytes_total and spd_bytes_used values

The value stored to 'spd_bytes_total' is never read. Now it is fixed.
This is spotted using clang-tool v9.
Also add a check if spd_bytes_used and/or spd_bytes_total are reserved
and make sure that spd_bytes_used is not greater than spd_bytes_total.

Change-Id: I426a7e64cc4c0bcced91d03387e02c8d965a21dc
Signed-off-by: Elyes HAOUAS 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35558
Tested-by: build bot (Jenkins) 
Reviewed-by: Nico Huber 
---
M src/device/dram/ddr4.c
1 file changed, 16 insertions(+), 2 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Nico Huber: Looks good to me, approved

diff --git a/src/device/dram/ddr4.c b/src/device/dram/ddr4.c
index 4f99ecc..07f9dec 100644
--- a/src/device/dram/ddr4.c
+++ b/src/device/dram/ddr4.c
@@ -111,17 +111,31 @@
    	return SPD_STATUS_INVALID;
    }

-	spd_bytes_total = (spd[0] >> 4) & ((1 << 3) - 1);
-	spd_bytes_used = spd[0] & ((1 << 4) - 1);
+	spd_bytes_total = (spd[0] >> 4) & 0x7;
+	spd_bytes_used = spd[0] & 0xf;

if (!spd_bytes_total || !spd_bytes_used) {
    	printk(BIOS_ERR, "SPD failed basic sanity checks\n");
    	return SPD_STATUS_INVALID;
    }

+	if (spd_bytes_total >= 3)
+		printk(BIOS_WARNING, "SPD Bytes Total value is reserved\n");
+
    spd_bytes_total = 256 << (spd_bytes_total - 1);
+
+	if (spd_bytes_used > 4) {
+		printk(BIOS_ERR, "SPD Bytes Used value is reserved\n");
+		return SPD_STATUS_INVALID;
+	}
+
    spd_bytes_used = spd_bytes_used_table[spd_bytes_used];

+	if (spd_bytes_used > spd_bytes_total) {
+		printk(BIOS_ERR, "SPD Bytes Used is greater than SPD Bytes Total\n");
+		return SPD_STATUS_INVALID;
+	}
+
    /* Verify CRC of blocks that have them, do not step over 'used' length */
    for (int i = 0; i < ARRAY_SIZE(spd_blocks); i++) {
    	/* this block is not checksumed */