arm64: compat: Clear the IT state independent of the 32-bit ARM or Thumb-2 mode

The ARM architecture reference specifies that the IT state bits in the
PSR must be all zeros in ARM mode or behavior is unspecified. If an ARM
function is registered as a signal handler, and that signal is delivered
inside a block of instructions following an IT instruction, some of the
instructions at the beginning of the signal handler may be skipped if
the IT state bits of the Program Status Register are not cleared by the
kernel.

Signed-off-by: T.J. Purtell <tj@mobisocial.us>
[catalin.marinas@arm.com: code comment and commit log updated]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index e8772c07cf5c9b38217b416c709ee1c5e0a657c7..e51bbe79f5b5b9c850207a577e42018caf5fa846 100644 (file)
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -446,12 +446,13 @@ static void compat_setup_return(struct pt_regs *regs, struct k_sigaction *ka,
        /* Check if the handler is written for ARM or Thumb */
        thumb = handler & 1;
 
-       if (thumb) {
+       if (thumb)
                spsr |= COMPAT_PSR_T_BIT;
-               spsr &= ~COMPAT_PSR_IT_MASK;
-       } else {
+       else
                spsr &= ~COMPAT_PSR_T_BIT;
-       }
+
+       /* The IT state must be cleared for both ARM and Thumb-2 */
+       spsr &= ~COMPAT_PSR_IT_MASK;
 
        if (ka->sa.sa_flags & SA_RESTORER) {
                retcode = ptr_to_compat(ka->sa.sa_restorer);