[PATCH v1 3/4] arm/syscalls: Specific usage of verify_pre_usermode_state

Russell King - ARM Linux
2017-03-08T21:49:56Z

On Wed, Mar 08, 2017 at 01:38:43PM -0800, 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

This really makes the fast exit utterly pointless, and we might as well
rip all that out.

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.