On Fri, Jan 15, 2021 at 12:00:42PM +0000, Vincenzo Frascino wrote:
> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
> index d02aff9f493d..1a715963d909 100644
> --- a/arch/arm64/include/asm/mte.h
> +++ b/arch/arm64/include/asm/mte.h
> @@ -92,5 +92,26 @@ static inline void mte_assign_mem_tag_range(void *addr,
> size_t size)
>
> #endif /* CONFIG_ARM64_MTE */
>
> +#ifdef CONFIG_KASAN_HW_TAGS
> +void mte_check_tfsr_el1_no_sync(void);
> +static inline void mte_check_tfsr_el1(void)
> +{
> + mte_check_tfsr_el1_no_sync();
> + /*
> + * The asynchronous faults are synch'ed automatically with
> + * TFSR_EL1 on kernel entry but for exit an explicit dsb()
> + * is required.
> + */
> + dsb(ish);
> +}
Mark commented already, the barrier should be above
mte_check_tfsr_el1_no_sync(). Regarding the ISB, we are waiting for
confirmation from the architects.
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index df7a1ae26d7c..6cb92e9d6ad1 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -180,6 +180,32 @@ void mte_enable_kernel(enum kasan_hw_tags_mode mode)
> isb();
> }
>
> +#ifdef CONFIG_KASAN_HW_TAGS
> +void mte_check_tfsr_el1_no_sync(void)
> +{
> + u64 tfsr_el1;
> +
> + if (!system_supports_mte())
> + return;
> +
> + tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
> +
> + /*
> + * The kernel should never hit the condition TF0 == 1
> + * at this point because for the futex code we set
> + * PSTATE.TCO.
> + */
> + WARN_ON(tfsr_el1 & SYS_TFSR_EL1_TF0);
I'd change this to a WARN_ON_ONCE() in case we trip over this due to
model bugs etc. and it floods the log.
> + if (tfsr_el1 & SYS_TFSR_EL1_TF1) {
> + write_sysreg_s(0, SYS_TFSR_EL1);
> + isb();
While in general we use ISB after a sysreg update, I haven't convinced
myself it's needed here. There's no side-effect to updating this reg and
a subsequent TFSR access should see the new value. If a speculated load
is allowed to update this reg, we'd probably need an ISB+DSB (I don't
think it does, something to check with the architects).
> +
> + pr_err("MTE: Asynchronous tag exception detected!");
We discussed this already, I think we should replace this pr_err() with
a call to kasan_report(). In principle, kasan already knows the mode as
it asked for sync/async but we could make this explicit and expand the
kasan API to take some argument (or have separate function like
kasan_report_async()).
--
Catalin
