firmware: qcom_scm: use 64-bit calling convention only when client is 64-bit

commit 3337a6fea25370d3d244ec6bb38c71ee86fcf837 upstream.

Per the "SMC calling convention specification", the 64-bit calling
convention can only be used when the client is 64-bit. Whereas the
32-bit calling convention can be used by either a 32-bit or a 64-bit
client.

Currently during SCM probe, irrespective of the client, 64-bit calling
convention is made, which is incorrect and may lead to the undefined
behaviour when the client is 32-bit. Let's fix it.

Cc: stable@vger.kernel.org
Fixes: 9a434cee773a ("firmware: qcom_scm: Dynamically support SMCCC and legacy conventions")
Reviewed-By: Elliot Berman <quic_eberman@quicinc.com>
Signed-off-by: Kathiravan Thirumoorthy <quic_kathirav@quicinc.com>
Link: https://lore.kernel.org/r/20230925-scm-v3-1-8790dff6a749@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
index 06fe8ac..69831f1 100644 (file)
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -168,6 +168,12 @@ static enum qcom_scm_convention __get_convention(void)
                return qcom_scm_convention;
 
        /*
+        * Per the "SMC calling convention specification", the 64-bit calling
+        * convention can only be used when the client is 64-bit, otherwise
+        * system will encounter the undefined behaviour.
+        */
+#if IS_ENABLED(CONFIG_ARM64)
+       /*
         * Device isn't required as there is only one argument - no device
         * needed to dma_map_single to secure world
         */
@@ -187,6 +193,7 @@ static enum qcom_scm_convention __get_convention(void)
                forced = true;
                goto found;
        }
+#endif
 
        probed_convention = SMC_CONVENTION_ARM_32;
        ret = __scm_smc_call(NULL, &desc, probed_convention, &res, true);