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>
(cherry picked from commit aa62c2091129af81a172350b718eb35d5448cebc)
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index e393174fe859721e7f6538bc377577cb69bb68aa..3edf7f48c54b29292b192464e03a8333452e5b9c 100644 (file)
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -474,12 +474,13 @@ 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);