[PATCH v4 01/13] efi/cper: Reject CPER records with an out-of-range error_data_length

cper_estatus_check() sizes each section with acpi_hest_get_record_size(),
which adds the firmware-controlled u32 error_data_length to the header size
as a signed int (see <acpi/ghes.h>). A value in the top sizeof(*gdata)
bytes of the u32 range wraps the sum small rather than large, so it slips
past the "record_size > data_len" check: against the 72-byte v300 header,
0xffffffb9 sizes the record at 1 and acpi_hest_get_next() walks it a byte
at a time, off the end. 0xffffffb8 sizes it at 0 and loops forever.

Sum in u64 so the check sees the real size, and reject a size the int
helpers cannot carry, since the walk advances by their return value.

This is the per-section upper bound the later "len < sizeof(*foo)" guards
rely on; they are lower bounds only.

Reported-by: [email protected]
Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
Fixes: 45b14a4ffcc1 ("efi: cper: Fix possible out-of-bounds access")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dave Jiang <[email protected]>
---
v4:
- Do the arithmetic in u64 at the choke point instead of bounding the u32
  error_data_length against data_len, so the check no longer depends on the
  signed helpers in <acpi/ghes.h> behaving (Tony Luck). Bounding the u32
  still left a window when data_length itself was within a header of
  U32_MAX, and it did not stop acpi_hest_get_next() advancing by a wrapped
  int. The v3 "< 0" arm was dead either way, since data_len is unsigned and
  promoted the int back (Tony Luck, Shuai Xue).
- Dropped Alison's and Shuai's Reviewed-by; the check was reworked after
  they reviewed it.
---
 drivers/firmware/efi/cper.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index 06b4fdb59917..ec092729cacc 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -752,7 +752,7 @@ EXPORT_SYMBOL_GPL(cper_estatus_check_header);
 int cper_estatus_check(const struct acpi_hest_generic_status *estatus)
 {
 	struct acpi_hest_generic_data *gdata;
-	unsigned int data_len, record_size;
+	unsigned int data_len;
 	int rc;
 
 	rc = cper_estatus_check_header(estatus);
@@ -762,11 +762,21 @@ int cper_estatus_check(const struct acpi_hest_generic_status *estatus)
 	data_len = estatus->data_length;
 
 	apei_estatus_for_each_section(estatus, gdata) {
+		u64 record_size;
+
 		if (acpi_hest_get_size(gdata) > data_len)
 			return -EINVAL;
 
-		record_size = acpi_hest_get_record_size(gdata);
-		if (record_size > data_len)
+		/*
+		 * acpi_hest_get_record_size() sums these as a signed int (see
+		 * <acpi/ghes.h>), which wraps small for a huge
+		 * error_data_length and slips past the check below. Sum in u64,
+		 * and reject what those helpers cannot carry, since the walk
+		 * advances by their return value.
+		 */
+		record_size = (u64)acpi_hest_get_size(gdata) +
+			      gdata->error_data_length;
+		if (record_size > data_len || record_size > INT_MAX)
 			return -EINVAL;
 
 		data_len -= record_size;
-- 
2.54.0