nrf_security: Fix 54lm20 alignment issue in Cracen

The Cracen in 54lm20 does not allow single byte writes
in the PK memory. There was some single byte writes in
Montgomery. This makes sure that the single byte writes
are done using the relevant sx_ functions which implement
workarounds for this issue when needed.

Ref: NCSDK-33957

Signed-off-by: Georgios Vasilakis <[email protected]>

Author: Vge0rge

subsys/nrf_security/src/drivers/cracen/silexpk/src/montgomery.c

@@ -34,11 +34,11 @@ struct sx_pk_acq_req sx_async_x25519_ptmult_go(const struct sx_x25519_op *k,
 	sx_wrpkmem(inputs.p.addr, pt->bytes, SX_X25519_OP_SZ);
 	sx_wrpkmem(inputs.k.addr, k->bytes, SX_X25519_OP_SZ);
 	/* clamp the scalar */
-	inputs.k.addr[31] |= 1 << 6;
-	inputs.k.addr[31] &= 0x7f;
-	inputs.k.addr[0] &= 0xF8;
+	sx_wrpkmem_byte(&inputs.k.addr[31], (inputs.k.addr[31] | 1 << 6) & 0x7f);
+	sx_wrpkmem_byte(&inputs.k.addr[0], inputs.k.addr[0] & 0xF8);
+
 	/* clamp the pt */
-	inputs.p.addr[31] &= 0x7f;
+	sx_wrpkmem_byte(&inputs.p.addr[31], inputs.p.addr[31] & 0x7f);
 
 	sx_pk_run(pkreq.req);
 
@@ -90,8 +90,8 @@ struct sx_pk_acq_req sx_async_x448_ptmult_go(const struct sx_x448_op *k,
 	sx_wrpkmem(inputs.p.addr, pt->bytes, SX_X448_OP_SZ);
 	sx_wrpkmem(inputs.k.addr, k->bytes, SX_X448_OP_SZ);
 	/* clamp the scalar */
-	inputs.k.addr[55] |= 0x80;
-	inputs.k.addr[0] &= 0xFC;
+	sx_wrpkmem_byte(&inputs.k.addr[55], inputs.k.addr[55] | 0x80);
+	sx_wrpkmem_byte(&inputs.k.addr[0], inputs.k.addr[0] & 0xFC);
 
 	sx_pk_run(pkreq.req);