On 1/13/21 6:11 PM, Catalin Marinas wrote:
> On Thu, Jan 07, 2021 at 05:29:07PM +0000, Vincenzo Frascino wrote:
>> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
>> index d02aff9f493d..a60d3718baae 100644
>> --- a/arch/arm64/include/asm/mte.h
>> +++ b/arch/arm64/include/asm/mte.h
>> @@ -39,6 +39,7 @@ void mte_free_tag_storage(char *storage);
>> /* track which pages have valid allocation tags */
>> #define PG_mte_tagged PG_arch_2
>>
>> +void mte_check_tfsr_el1(void);
>> void mte_sync_tags(pte_t *ptep, pte_t pte);
>> void mte_copy_page_tags(void *kto, const void *kfrom);
>> void flush_mte_state(void);
>> @@ -56,6 +57,9 @@ void mte_assign_mem_tag_range(void *addr, size_t size);
>> /* unused if !CONFIG_ARM64_MTE, silence the compiler */
>> #define PG_mte_tagged 0
>>
>> +static inline void mte_check_tfsr_el1(void)
>> +{
>> +}
>
> I think we should enable this dummy function when !CONFIG_KASAN_HW_TAGS.
> It saves us an unnecessary function call in a few places.
>
Ok, I will add it in v3.
>> static inline void mte_sync_tags(pte_t *ptep, pte_t pte)
>> {
>> }
>> diff --git a/arch/arm64/kernel/entry-common.c
>> b/arch/arm64/kernel/entry-common.c
>> index 5346953e4382..74b020ce72d7 100644
>> --- a/arch/arm64/kernel/entry-common.c
>> +++ b/arch/arm64/kernel/entry-common.c
>> @@ -37,6 +37,8 @@ static void noinstr enter_from_kernel_mode(struct pt_regs
>> *regs)
>> lockdep_hardirqs_off(CALLER_ADDR0);
>> rcu_irq_enter_check_tick();
>> trace_hardirqs_off_finish();
>> +
>> + mte_check_tfsr_el1();
>> }
>>
>> /*
>> @@ -47,6 +49,8 @@ static void noinstr exit_to_kernel_mode(struct pt_regs
>> *regs)
>> {
>> lockdep_assert_irqs_disabled();
>>
>> + mte_check_tfsr_el1();
>> +
>> if (interrupts_enabled(regs)) {
>> if (regs->exit_rcu) {
>> trace_hardirqs_on_prepare();
>> @@ -243,6 +247,8 @@ asmlinkage void noinstr enter_from_user_mode(void)
>>
>> asmlinkage void noinstr exit_to_user_mode(void)
>> {
>> + mte_check_tfsr_el1();
>
> While for kernel entry the asynchronous faults are sync'ed automatically
> with TFSR_EL1, we don't have this for exit, so we'd need an explicit
> DSB. But rather than placing it here, it's better if we add a bool sync
> argument to mte_check_tfsr_el1() which issues a dsb() before checking
> the register. I think that's the only place where such argument would be
> true (for now).
>
Good point, I will add the dsb() in mte_check_tfsr_el1() but instead of a bool
parameter I will add something more explicit.
>> +
>> trace_hardirqs_on_prepare();
>> lockdep_hardirqs_on_prepare(CALLER_ADDR0);
>> user_enter_irqoff();
>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
>> index 5d992e16b420..26030f0b79fe 100644
>> --- a/arch/arm64/kernel/mte.c
>> +++ b/arch/arm64/kernel/mte.c
>> @@ -185,6 +185,34 @@ void mte_enable_kernel(enum kasan_arg_mode mode)
>> isb();
>> }
>>
>> +void mte_check_tfsr_el1(void)
>> +{
>> + u64 tfsr_el1;
>> +
>> + if (!IS_ENABLED(CONFIG_KASAN_HW_TAGS))
>> + return;
>
> If we define the static inline when !CONFIG_KASAN_HW_TAGS, we could add
> the #ifdef here around the whole function.
>
Ok. I will add it in v3.
>> + 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);
>> +
>> + if (tfsr_el1 & SYS_TFSR_EL1_TF1) {
>> + write_sysreg_s(0, SYS_TFSR_EL1);
>> + isb();
>> +
>> + pr_err("MTE: Asynchronous tag exception detected!");
>> + }
>> +}
>> +NOKPROBE_SYMBOL(mte_check_tfsr_el1);
>
> Do we need this to be NOKPROBE_SYMBOL? It's not that low level.
>
It is an inheritance from when I had this code called very early. I will remove
it in the next version.
>> +
>> static void update_sctlr_el1_tcf0(u64 tcf0)
>> {
>> /* ISB required for the kernel uaccess routines */
>> @@ -250,6 +278,15 @@ void mte_thread_switch(struct task_struct *next)
>> /* avoid expensive SCTLR_EL1 accesses if no change */
>> if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
>> update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
>> +
>> + /*
>> + * Check if an async tag exception occurred at EL1.
>> + *
>> + * Note: On the context switch patch we rely on the dsb() present
>
> s/patch/path/
>
>> + * in __switch_to() to guaranty that the indirect writes to TFSR_EL1
>
> s/guaranty/guarantee/ (well, still valid though I think rarely used).
>
>> + * are synchronized before this point.
>> + */
>> + mte_check_tfsr_el1();
>> }
>>
>> void mte_suspend_exit(void)
>> --
>> 2.30.0
>
--
Regards,
Vincenzo
