[PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Roman Skakun <roman_skakun@xxxxxxxx>]

This patch added additional sanity and increases an understanding for
getting proper value from the first argument for SMC call on aarch64
according to SMCC Convention.

[0] ARM DEN0028B, page 12

Signed-off-by: Roman Skakun <roman_skakun@xxxxxxxx>
---
 xen/arch/arm/tee/optee.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index ee85359742..87060b52b8 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
     if ( !ctx )
         return false;
 
-    switch ( get_user_reg(regs, 0) )
+    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */
+    switch ( (uint32_t)get_user_reg(regs, 0) )
     {
     case OPTEE_SMC_CALLS_COUNT:
         set_user_reg(regs, 0, OPTEE_MEDIATOR_SMC_COUNT);
-- 
2.25.1