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

Thomas Garnier
2017-03-08T22:33:47Z

Make sense, as discussed on patch number one, I will write custom
assembly for each architecture when BUG_ON is not required. I will try
to use macros to make it easier to read.

On Wed, Mar 8, 2017 at 2:05 PM, Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> 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

--
Thomas