[PATCH v2] efi_loader: fix use after free in efi_exit() with tcg2

[Vincent Stehlé]

The efi_exit() function frees the loaded image memory by calling
efi_delete_image(). However, when CONFIG_EFI_TCG2_PROTOCOL is enabled, the
image_obj->image_type structure member is accessed after the memory has
been freed.

Fix this by performing the tcg2 measurement before the image deletion.

Fixes: 8fc4e0b4273a ("efi_loader: add boot variable measurement")
Suggested-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
Signed-off-by: Vincent Stehlé <vincent.stehle at arm.com>
Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
Cc: Tom Rini <trini at konsulko.com>
Cc: Masahisa Kojima <kojima.masahisa at socionext.com>
---

Hi,

Here is a respin after feedbacks. [1]

Changes for v2:
- Move the event measurement before image deletion instead of keeping a
  copy of image_type (thanks Ilias!)

This can be verified with sandbox_defconfig + CONFIG_VALGRIND=y and the
following command:

  valgrind --suppressions=scripts/u-boot.supp \
    ./u-boot -T -c "setenv efi_selftest start image return; \
                    bootefi selftest"

This was lightly tested for regression with sandbox_defconfig and the
following commands:

  ./u-boot -T -c "ut measurement"

  ./test/py/test.py --build-dir="$PWD" -s -k "test_efi_bootmgr \
	or test_efi_loader or test_efi_selftest or test_efi_secboot"

Adding some instrumentation in efi_exit() and tcg2_log_append() shows no
change in the event measurements sequence.

[1] https://lore.kernel.org/u-boot/20260123105814.1083834-1-vincent.stehle@arm.com/

 lib/efi_loader/efi_boottime.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index ddc935d2240..b424d924896 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -3494,12 +3494,6 @@ static efi_status_t EFIAPI efi_exit(efi_handle_t image_handle,
 		if (ret != EFI_SUCCESS)
 			EFI_PRINT("%s: out of memory\n", __func__);
 	}
-	/* efi_delete_image() frees image_obj. Copy before the call. */
-	exit_jmp = image_obj->exit_jmp;
-	*image_obj->exit_status = exit_status;
-	if (image_obj->image_type == IMAGE_SUBSYSTEM_EFI_APPLICATION ||
-	    exit_status != EFI_SUCCESS)
-		efi_delete_image(image_obj, loaded_image_protocol);
 
 	if (IS_ENABLED(CONFIG_EFI_TCG2_PROTOCOL)) {
 		if (image_obj->image_type == IMAGE_SUBSYSTEM_EFI_APPLICATION) {
@@ -3510,6 +3504,13 @@ static efi_status_t EFIAPI efi_exit(efi_handle_t image_handle,
 		}
 	}
 
+	/* efi_delete_image() frees image_obj. Copy before the call. */
+	exit_jmp = image_obj->exit_jmp;
+	*image_obj->exit_status = exit_status;
+	if (image_obj->image_type == IMAGE_SUBSYSTEM_EFI_APPLICATION ||
+	    exit_status != EFI_SUCCESS)
+		efi_delete_image(image_obj, loaded_image_protocol);
+
 	/* Make sure entry/exit counts for EFI world cross-overs match */
 	EFI_EXIT(exit_status);
 
-- 
2.51.0