firmware: arm_ffa: Explicitly cast return value from FFA_VERSION before comparison

JIRA: https://issues.redhat.com/browse/RHEL-102691

commit cecf6a5
Author: Sudeep Holla <sudeep.holla@arm.com>
Date: Fri, 21 Feb 2025 09:56:31 +0000

    The return value ver.a0 is unsigned long type and FFA_RET_NOT_SUPPORTED
    is a negative value.

    Since the return value from the firmware can be just 32-bit even on
    64-bit systems as FFA specification mentions it as int32 error code in
    w0 register, explicitly casting to s32 ensures correct sign interpretation
    when comparing against a signed error code FFA_RET_NOT_SUPPORTED.

    Without casting, comparison between unsigned long and a negative
    constant could lead to unintended results due to type promotions.

    Fixes: 3bbfe98 ("firmware: arm_ffa: Add initial Arm FFA driver support")
    Reported-by: Andrei Homescu <ahomescu@google.com>
    Message-Id: <20250221095633.506678-1-sudeep.holla@arm.com>
    Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Signed-off-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>

Author: hrw

drivers/firmware/arm_ffa/driver.c

@@ -144,7 +144,7 @@ static int ffa_version_check(u32 *version)
 		      .a0 = FFA_VERSION, .a1 = FFA_DRIVER_VERSION,
 		      }, &ver);
 
-	if (ver.a0 == FFA_RET_NOT_SUPPORTED) {
+	if ((s32)ver.a0 == FFA_RET_NOT_SUPPORTED) {
 		pr_info("FFA_VERSION returned not supported\n");
 		return -EOPNOTSUPP;
 	}