linux-kernel - [PATCH v5 4/4] efi/cper: don't dump the entire memory region

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Message-ID: <f47447094cfa388042ed3563acaeb06c98ee5248.1767804050.git.mchehab+huawei@kernel.org>
Date: Wed,  7 Jan 2026 17:41:52 +0100
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>
Cc: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
	acpica-devel@...ts.linux.dev,
	linux-acpi@...r.kernel.org,
	linux-edac@...r.kernel.org,
	linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v5 4/4] efi/cper: don't dump the entire memory region

The current logic at cper_print_fw_err() doesn't check if the
error record length is big enough to handle offset. On a bad firmware,
if the ofset is above the actual record, length -= offset will
underflow, making it dump the entire memory.

The end result can be:

- the logic taking a lot of time dumping large regions of memory;
- data disclosure due to the memory dumps;
- an OOPS, if it tries to dump an unmapped memory region.

Fix it by checking if the section length is too small before doing
a hex dump.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
---
 drivers/firmware/efi/cper.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index 88fc0293f876..0e938fc5ccb1 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -560,6 +560,11 @@ static void cper_print_fw_err(const char *pfx,
 	} else {
 		offset = sizeof(*fw_err);
 	}
+	if (offset > length) {
+		printk("%s""error section length is too small: offset=%d, length=%d\n",
+		       pfx, offset, length);
+		return;
+	}
 
 	buf += offset;
 	length -= offset;
-- 
2.52.0