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SubjectRe: [PATCH v11 4/5] arm64: mte: Enable async tag check fault
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On 2/5/21 3:39 PM, Catalin Marinas wrote:
> On Sat, Jan 30, 2021 at 04:52:24PM +0000, Vincenzo Frascino wrote:
>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
>> index 92078e1eb627..7763ac1f2917 100644
>> --- a/arch/arm64/kernel/mte.c
>> +++ b/arch/arm64/kernel/mte.c
>> @@ -182,6 +182,37 @@ bool mte_report_once(void)
>> return READ_ONCE(report_fault_once);
>> }
>>
>> +#ifdef CONFIG_KASAN_HW_TAGS
>> +void mte_check_tfsr_el1(void)
>> +{
>> + u64 tfsr_el1;
>> +
>> + if (!system_supports_mte())
>> + return;
>> +
>> + tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
>> +
>> + /*
>> + * The kernel should never trigger an asynchronous fault on a
>> + * TTBR0 address, so we should never see TF0 set.
>> + * For futexes we disable checks via PSTATE.TCO.
>> + */
>> + WARN_ONCE(tfsr_el1 & SYS_TFSR_EL1_TF0,
>> + "Kernel async tag fault on TTBR0 address");
>
> Sorry, I got confused when I suggested this warning. If the user is
> running in async mode, the TFSR_EL1.TF0 bit may be set by
> copy_mount_options(), strncpy_from_user() which rely on an actual fault
> happening (not the case with asynchronous where only a bit is set). With
> the user MTE support, we never report asynchronous faults caused by the
> kernel on user addresses as we can't easily track them. So this warning
> may be triggered on correctly functioning kernel/user.
>

No issue, I will re-post removing the WARN_ONCE().

>> +
>> + if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) {
>> + /*
>> + * Note: isb() is not required after this direct write
>> + * because there is no indirect read subsequent to it
>> + * (per ARM DDI 0487F.c table D13-1).
>> + */
>> + write_sysreg_s(0, SYS_TFSR_EL1);
>
> Zeroing the whole register is still fine, we don't care about the TF0
> bit anyway.
>
>> +
>> + kasan_report_async();
>> + }
>> +}
>> +#endif
>

--
Regards,
Vincenzo

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