[PATCH 1/1] rsa: fix retrieving public exponent on big-endian systems

[Tom Rini <trini@konsulko.com>]

On Tue, Oct 06, 2020 at 12:09:45PM +0200, Rasmus Villemoes wrote:

> Commit fdf0819afb (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: fdf0819afb ("rsa: fix alignment issue when getting public exponent")
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> Reviewed-by: Simon Glass <sjg@chromium.org>

Applied to u-boot/master, thanks!

-- 
Tom
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