[PATCH v3 08/10] ACPI: APEI: GHES: Validate memory error section length before payload access

sashiko-bot flagged that the memory error length check was placed too
late, leaving the other payload consumers unprotected.

ghes_do_proc() hands the CPER_SEC_PLATFORM_MEM payload to the report
chain, arch_apei_report_mem_error() and ghes_handle_memory_failure()
without checking gdata->error_data_length. These read validation_bits
and physical_addr (offsets 0 and 16), so a shorter section reads past the
record.

Validate error_data_length once in ghes_do_proc(), before any consumer
runs, so every consumer is covered. Bound against struct
cper_sec_mem_err_old (the UEFI 2.1/2.2 layout) rather than the full
struct: the section length is authoritative, older firmware legitimately
emits the shorter record, and the trailing fields, though packed
unconditionally by cper_mem_err_pack(), are only acted on under
validation bits that a short record leaves clear. This matches the lower
bound already used in drivers/firmware/efi/cper.c.

A malformed sub-record no longer reaches ghes_handle_memory_failure().

Reported-by: [email protected]
Closes: https://sashiko.dev/#/patchset/[email protected]?part=7
Fixes: ca104edc1784 ("ACPI, APEI, GHES: Cleanup ghes memory error handling")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dave Jiang <[email protected]>
---
v3:
- Move the length check into ghes_do_proc() so the report chain and arch
  reporter are covered too, and bound against the older UEFI 2.1/2.2
  layout instead of the full struct (sashiko).
---
 drivers/acpi/apei/ghes.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index b8dbd99da47e..1d2966a437bd 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -940,6 +940,17 @@ static void ghes_do_proc(struct ghes *ghes,
 		if (guid_equal(sec_type, &CPER_SEC_PLATFORM_MEM)) {
 			struct cper_sec_mem_err *mem_err = acpi_hest_get_payload(gdata);
 
+			/*
+			 * Several consumers below dereference the record, so
+			 * check the length once here. Bound against the shorter
+			 * UEFI 2.1/2.2 layout that older firmware still emits;
+			 * the extra fields are only used under validation bits
+			 * such records leave clear.
+			 */
+			if (gdata->error_data_length <
+			    sizeof(struct cper_sec_mem_err_old))
+				continue;
+
 			atomic_notifier_call_chain(&ghes_report_chain, sev, mem_err);
 
 			arch_apei_report_mem_error(sev, mem_err);
-- 
2.55.0