[PATCH] lib: rsa: Fix unaligned 64-bit fdt accesses

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

The fdt only provides 32-bit alignment of data. If the public_exponent
happens to be not 64-bit aligned, we can trigger an exception on certain
architectures. Seen on TI AM64x.

Note that the normal way of accessing such a number would be
fdtdec_get_number. However, this is not available for tools, and this
is one use case for lib/rsa.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 lib/rsa/rsa-mod-exp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/rsa/rsa-mod-exp.c b/lib/rsa/rsa-mod-exp.c
index 420ab2eba0..4b9c4b1459 100644
--- a/lib/rsa/rsa-mod-exp.c
+++ b/lib/rsa/rsa-mod-exp.c
@@ -246,6 +246,11 @@ static void rsa_convert_big_endian(uint32_t *dst, const uint32_t *src, int len)
 		dst[i] = fdt32_to_cpu(src[len - 1 - i]);
 }
 
+static uint64_t fdt64_get(const uint32_t *data)
+{
+	return ((uint64_t)fdt32_to_cpu(data[0]) << 32) | fdt32_to_cpu(data[1]);
+}
+
 int rsa_mod_exp_sw(const uint8_t *sig, uint32_t sig_len,
 		struct key_prop *prop, uint8_t *out)
 {
@@ -262,8 +267,7 @@ int rsa_mod_exp_sw(const uint8_t *sig, uint32_t sig_len,
 	if (!prop->public_exponent)
 		key.exponent = RSA_DEFAULT_PUBEXP;
 	else
-		key.exponent =
-			fdt64_to_cpu(*((uint64_t *)(prop->public_exponent)));
+		key.exponent = fdt64_get(prop->public_exponent);
 
 	if (!key.len || !prop->modulus || !prop->rr) {
 		debug("%s: Missing RSA key info", __func__);
-- 
2.26.1