On Wed, 8 Mar 2017, Thomas Garnier wrote: > Implement specific usage of verify_pre_usermode_state for user-mode > returns for arm. > --- > Based on next-20170308 > --- > arch/arm/Kconfig | 1 + > arch/arm/kernel/entry-common.S | 5 +++++ > 2 files changed, 6 insertions(+) > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 0d4e71b42c77..704fd8f197fa 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -12,6 +12,7 @@ config ARM > select ARCH_HAVE_CUSTOM_GPIO_H > select ARCH_HAS_GCOV_PROFILE_ALL > select ARCH_MIGHT_HAVE_PC_PARPORT > + select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE > select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX > select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7 > select ARCH_SUPPORTS_ATOMIC_RMW > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index eb5cd77bf1d8..80cfdc7fabde 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -39,6 +39,9 @@ > ret_fast_syscall: > UNWIND(.fnstart ) > UNWIND(.cantunwind ) > + push {r0} @ save returned r0 > + bl verify_pre_usermode_state > + pop {r0} @ restore r0 > disable_irq_notrace @ disable interrupts > ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
This feature is configurable, right? Here the branch overhead is imposed even if the feature is configured out. You should consider conditionally defining a macro like some other features do. Furthermore I think we still support old toolchains that don't know what push and pop mean. You should use the legacy syntax instead. Nicolas