linux-hardening - [PATCH v2 1/4] efi: pstore: Request at most 512 bytes for variable names

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Date: Thu, 28 Mar 2024 21:50:30 +0100
From: Tim Schumacher <timschumi@....de>
To: linux-efi@...r.kernel.org
Cc: Tim Schumacher <timschumi@....de>,
	Ard Biesheuvel <ardb@...nel.org>,
	linux-hardening@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>
Subject: [PATCH v2 1/4] efi: pstore: Request at most 512 bytes for variable names

Work around a quirk in a few old (2011-ish) UEFI implementations, where
a call to `GetNextVariableName` with a buffer size larger than 512 bytes
will always return EFI_INVALID_PARAMETER.

This was already done to efivarfs in commit f45812cc23fb ("efivarfs:
Request at most 512 bytes for variable names"), but the second copy of
the variable iteration implementation was overlooked.

Signed-off-by: Tim Schumacher <timschumi@....de>
---
Changes from v1:
 - None, resubmitted as a part of a chain.
---
 drivers/firmware/efi/efi-pstore.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 833cbb995dd3f..5b9dc26e6bcb9 100644
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -162,7 +162,15 @@ static ssize_t efi_pstore_read(struct pstore_record *record)
 	efi_status_t status;

 	for (;;) {
-		varname_size = 1024;
+		/*
+		 * A small set of old UEFI implementations reject sizes
+		 * above a certain threshold, the lowest seen in the wild
+		 * is 512.
+		 *
+		 * TODO: Commonize with the iteration implementation in
+		 *       fs/efivarfs to keep all the quirks in one place.
+		 */
+		varname_size = 512;

 		/*
 		 * If this is the first read() call in the pstore enumeration,
--
2.44.0