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SubjectRe: [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors
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On 12/06/2018 06:25 PM, Catalin Marinas wrote:
> On Mon, Dec 03, 2018 at 01:55:18PM +0000, Julien Thierry wrote:
>> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
>> index 07c3408..cabfcae 100644
>> --- a/arch/arm64/include/asm/uaccess.h
>> +++ b/arch/arm64/include/asm/uaccess.h
>> @@ -233,6 +233,23 @@ static inline void uaccess_enable_not_uao(void)
>> __uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
>> }
>>
>> +#define unsafe_user_region_active uaccess_region_active
>> +static inline bool uaccess_region_active(void)
>> +{
>> + if (system_uses_ttbr0_pan()) {
>> + u64 ttbr;
>> +
>> + ttbr = read_sysreg(ttbr1_el1);
>> + return ttbr & TTBR_ASID_MASK;
>
> Nitpick: could write this in 1-2 lines.
>

True, I can do that in 1 line.

>> + } else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO)) {
>> + return (read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN) ?
>> + false :
>> + !read_sysreg_s(SYS_PSTATE_PAN);
>> + }
>
> ARM64_ALT_PAN_NOT_UAO implies ARM64_HAS_PAN which implies SCTLR_EL1.SPAN
> is 0 at run-time. Is this to cope with the case of being called prior to
> cpu_enable_pan()?
>

Yes, the issue I can into is that for cpufeatures, .cpu_enable()
callbacks are called inside stop_machine() which obviously might_sleep
and so attempts to check whether user_access is on. But for features
that get enabled before PAN, the PAN bit will be set.

Thanks,

Julien

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