[xen staging] xen/riscv: refactor decode_trap_cause()

[patchbot@xxxxxxx]

commit 10eccbb821cbd0d623ba3cb68a01dfb79c39ea48
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Tue Aug 6 08:36:29 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Aug 6 08:36:29 2024 +0200

    xen/riscv: refactor decode_trap_cause()
    
    Use array_access_nospec() to prevent guest speculation.
    
    Avoid double access of trap_causes[cause].
    
    Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/riscv/traps.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index cb18b30ff2..7149504ebc 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -6,6 +6,7 @@
  */
 
 #include <xen/lib.h>
+#include <xen/nospec.h>
 #include <xen/sched.h>
 
 #include <asm/processor.h>
@@ -47,9 +48,11 @@ static const char *decode_trap_cause(unsigned long cause)
         [CAUSE_STORE_GUEST_PAGE_FAULT] = "Guest Store/AMO Page Fault",
     };
 
-    if ( cause < ARRAY_SIZE(trap_causes) && trap_causes[cause] )
-        return trap_causes[cause];
-    return "UNKNOWN";
+    const char *res = cause < ARRAY_SIZE(trap_causes)
+                      ? array_access_nospec(trap_causes, cause)
+                      : NULL;
+
+    return res ?: "UNKNOWN";
 }
 
 static const char *decode_reserved_interrupt_cause(unsigned long irq_cause)
--
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