For a compressed kernel_noload image, bootm_load_os() allocates a decompression buffer of ALIGN(image_len * 4, SZ_1M) and then passes CONFIG_SYS_BOOTM_LEN (typically 128 MiB on arm64) to image_decomp() as the output limit. The decompressors honour whatever limit they are given, so a kernel that decompresses to more than four times its compressed size runs past the end of the allocated buffer and silently corrupts adjacent memory.
A 4x compression ratio is at the edge of what modern compressors (zstd, xz) achieve on real kernels, and is trivially exceeded by crafted, highly compressible payloads, so this is reachable both accidentally and intentionally. The overflow can land on already-loaded boot artefacts (FDT, ramdisk, loadables), U-Boot's own data, or memory-mapped device registers; the existing post-decompression overlap check in bootm_load_os() only catches overlap with the FIT itself. Patch 1 plumbs the actual allocation size through to image_decomp() and handle_decomp_error() via a single decomp_len variable, so decompression stops at the buffer boundary and fails cleanly when the image is too large. The non-noload code path is unchanged and continues to use CONFIG_SYS_BOOTM_LEN. Patch 2 adds a sandbox py-test that builds a FIT with a compressed kernel_noload image whose decompressed size exceeds the per-image buffer, and asserts that 'bootm loados' reports the failure instead of overflowing. Tested on sandbox: the new test passes; the existing test_fit_compressed_images_load (which covers the load-address path) and the other tests in test/py/tests/test_fit.py continue to pass. Aristo Chen (2): bootm: fix overflow of the noload kernel decompression buffer test/py: test kernel_noload decompression buffer overflow boot/bootm.c | 11 ++--- test/py/tests/test_fit.py | 84 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 90 insertions(+), 5 deletions(-) -- 2.43.0
