[PATCH] rsa: fix alignment issue when getting public exponent

Simon Glass sjg at chromium.org
Mon May 4 16:17:52 CEST 2020

+Tom Rini

On Sun, 3 May 2020 at 05:26, Heiko Stuebner <heiko at sntech.de> wrote:
> From: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
> To fill the exponent field of the rsa_public_key struct, rsa_mod_exp_sw
> did a cast to uint64_t of the key_prop->public_exponent field.
> But that alignment is not guaranteed in all cases.
> This came to light when in my spl-fit-signature the key-name exceeded
> a certain length and with it the verification then started failing.
> (naming it "integrity" worked fine, "integrity-uboot" failed)
> key_prop.public_exponent itself is actually a void-pointer, fdt_getprop()
> also just returns such a void-pointer and inside the devicetree the 64bit
> exponent is represented as 2 32bit numbers, so assuming a 64bit alignment
> can lead to false reads.
> So just use the already existing rsa_convert_big_endian() to do the actual
> conversion from the dt's big-endian to the needed uint64 value.
> Fixes: fc2f4246b4b3 ("rsa: Split the rsa-verify to separate the modular exponentiation")
> Signed-off-by: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
> ---
>  lib/rsa/rsa-mod-exp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Nice find! This probably changed when we updated the DT recently since
the unaligned-access thing was reverted I think. Or has this problem
been there forever?

Reviewed-by: Simon Glass <sjg at chromium.org>

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