hw: arm: Support direct boot for Linux/arm64 EFI zboot images

Fedora 39 will ship its arm64 kernels in the new generic EFI zboot
format, using gzip compression for the payload.

For doing EFI boot in QEMU, this is completely transparent, as the
firmware or bootloader will take care of this. However, for direct
kernel boot without firmware, we will lose the ability to boot such
distro kernels unless we deal with the new format directly.

EFI zboot images contain metadata in the header regarding the placement
of the compressed payload inside the image, and the type of compression
used. This means we can wire up the existing gzip support without too
much hassle, by parsing the header and grabbing the payload from inside
the loaded zboot image.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Alex Bennée <alex.bennee@linaro.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-id: 20230303160109.3626966-1-ardb@kernel.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: tweaked comment formatting, fixed checkpatch nits]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/hw/loader.h b/include/hw/loader.h
index 1384796..c4c1417 100644
--- a/include/hw/loader.h
+++ b/include/hw/loader.h
@@ -86,6 +86,25 @@ ssize_t load_image_gzipped_buffer(const char *filename, uint64_t max_sz,
                                   uint8_t **buffer);
 ssize_t load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz);
 
+/**
+ * unpack_efi_zboot_image:
+ * @buffer: pointer to a variable holding the address of a buffer containing the
+ *          image
+ * @size: pointer to a variable holding the size of the buffer
+ *
+ * Check whether the buffer contains a EFI zboot image, and if it does, extract
+ * the compressed payload and decompress it into a new buffer. If successful,
+ * the old buffer is freed, and the *buffer and size variables pointed to by the
+ * function arguments are updated to refer to the newly populated buffer.
+ *
+ * Returns 0 if the image could not be identified as a EFI zboot image.
+ * Returns -1 if the buffer contents were identified as a EFI zboot image, but
+ * unpacking failed for any reason.
+ * Returns the size of the decompressed payload if decompression was performed
+ * successfully.
+ */
+ssize_t unpack_efi_zboot_image(uint8_t **buffer, int *size);
+
 #define ELF_LOAD_FAILED       -1
 #define ELF_LOAD_NOT_ELF      -2
 #define ELF_LOAD_WRONG_ARCH   -3