rsa: fix retrieving public exponent on big-endian systems
Commit fdf0819a (rsa: fix alignment issue when getting public exponent) changed the logic to avoid doing an 8-byte access to a possibly-not-8-byte-aligned address. However, using rsa_convert_big_endian is wrong: That function converts an array of big-endian (32-bit) words with the most significant word first (aka a BE byte array) to an array of cpu-endian words with the least significant word first. While the exponent is indeed _stored_ as a big-endian 64-bit word (two BE words with MSW first), we want to extract it as a cpu-endian 64 bit word. On a little-endian host, swapping the words and byte-swapping each 32-bit word works, because that's the same as byte-swapping the whole 64 bit word. But on a big-endian host, the fdt32_to_cpu are no-ops, but rsa_convert_big_endian() still does the word-swapping, breaking verified boot. To fix that, while still ensuring we don't do unaligned accesses, add a little helper that first memcpy's the bytes to a local fdt64_t, then applies fdt64_to_cpu(). [The name is chosen based on the [bl]eXX_to_cpup in linux/byteorder/generic.h]. Fixes: fdf0819a ("rsa: fix alignment issue when getting public exponent") Signed-off-by: NRasmus Villemoes <rasmus.villemoes@prevas.dk> Reviewed-by: NSimon Glass <sjg@chromium.org>
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