[tip: efi/urgent] efi/libstub: arm64: Warn when efi_random_alloc() fails

[tip-bot2 for Ard Biesheuvel]

The following commit has been merged into the efi/urgent branch of tip:

Commit-ID:     ff80ef5bf5bd59e5eab82d1d846acc613ebbf6c4
Gitweb:        https://git.kernel.org/tip/ff80ef5bf5bd59e5eab82d1d846acc613ebbf6c4
Author:        Ard Biesheuvel <ardb@xxxxxxxxxx>
AuthorDate:    Mon, 26 Jul 2021 16:24:01 +02:00
Committer:     Ard Biesheuvel <ardb@xxxxxxxxxx>
CommitterDate: Tue, 03 Aug 2021 07:43:07 +02:00

efi/libstub: arm64: Warn when efi_random_alloc() fails

Randomization of the physical load address of the kernel image relies on
efi_random_alloc() returning successfully, and currently, we ignore any
failures and just carry on, using the ordinary, non-randomized page
allocator routine. This means we never find out if a failure occurs,
which could harm security, so let's at least warn about this condition.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Tested-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/firmware/efi/libstub/arm64-stub.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 6f214c9..010564f 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -130,6 +130,8 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 		 */
 		status = efi_random_alloc(*reserve_size, min_kimg_align,
 					  reserve_addr, phys_seed);
+		if (status != EFI_SUCCESS)
+			efi_warn("efi_random_alloc() failed: 0x%lx\n", status);
 	} else {
 		status = EFI_OUT_OF_RESOURCES;
 	}