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@kernel.org>
Tested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 6f214c9..010564f 100644 (file)
--- 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;
        }