On 9/30/19 4:14 PM, Andrew Jones wrote:
> On Mon, Sep 30, 2019 at 04:09:49PM +0100, Alexandru Elisei wrote:
>> Hi,
>>
>> On 9/30/19 3:53 PM, Andrew Jones wrote:
>>
>>> On Mon, Sep 30, 2019 at 03:25:07PM +0100, Alexandru Elisei wrote:
>>>> The PTE_USER bit (AP[1]) in a page entry means that lower privilege levels
>>>> (EL0, on arm64, or PL0, on arm) can read and write from that memory
>>>> location [1][2]. On arm64, it also implies PXN (Privileged execute-never)
>>>> when is set [3]. Add a function to clear the bit which we can use when we
>>>> want to execute code from that page or the prevent access from lower
>>>> exception levels.
>>>>
>>>> Make it available to arm too, in case someone needs it at some point.
>>>>
>>>> [1] ARM DDI 0406C.d, Table B3-6
>>>> [2] ARM DDI 0487E.a, table D5-28
>>>> [3] ARM DDI 0487E.a, table D5-33
>>>>
>>>> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
>>>> ---
>>>> lib/arm/asm/mmu-api.h | 1 +
>>>> lib/arm/mmu.c | 15 +++++++++++++++
>>>> 2 files changed, 16 insertions(+)
>>>>
>>>> diff --git a/lib/arm/asm/mmu-api.h b/lib/arm/asm/mmu-api.h
>>>> index df3ccf7bc7e0..8fe85ba31ec9 100644
>>>> --- a/lib/arm/asm/mmu-api.h
>>>> +++ b/lib/arm/asm/mmu-api.h
>>>> @@ -22,4 +22,5 @@ extern void mmu_set_range_sect(pgd_t *pgtable, uintptr_t virt_offset,
>>>> extern void mmu_set_range_ptes(pgd_t *pgtable, uintptr_t virt_offset,
>>>> phys_addr_t phys_start, phys_addr_t phys_end,
>>>> pgprot_t prot);
>>>> +extern void mmu_clear_user(unsigned long vaddr);
>>>> #endif
>>>> diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
>>>> index 3d38c8397f5a..78db22e6af14 100644
>>>> --- a/lib/arm/mmu.c
>>>> +++ b/lib/arm/mmu.c
>>>> @@ -217,3 +217,18 @@ unsigned long __phys_to_virt(phys_addr_t addr)
>>>> assert(!mmu_enabled() || __virt_to_phys(addr) == addr);
>>>> return addr;
>>>> }
>>>> +
>>>> +void mmu_clear_user(unsigned long vaddr)
>>>> +{
>>>> + pgd_t *pgtable;
>>>> + pteval_t *pte;
>>>> +
>>>> + if (!mmu_enabled())
>>>> + return;
>>>> +
>>>> + pgtable = current_thread_info()->pgtable;
>>>> + pte = get_pte(pgtable, vaddr);
>>>> +
>>>> + *pte &= ~PTE_USER;
>>>> + flush_tlb_page(vaddr);
>>>> +}
>>>> --
>>>> 2.20.1
>>>>
>>> This is fine, but I think you could just export get_pte() and then
>>> implement the PTE_USER clearing in the cache unit test instead. Anyway,
>> I thought about that, but I opted to make this a library function because I
>> would like to modify it to also act on block mappings and use it in patch #4
>> from the EL2 series (the patch that adds the prefetch abort test), and send
>> that change as part of the EL2 series. I am assuming that this patch set
>> will get merged before the EL2 series.
> Yeah, I need to get back to that EL2 series. I just need to wrap up a
> couple more things and then I'll be able to focus on it. If you have
> some plans to refresh it, then feel free to do that now. When I get
> back to it, I'll just jump into the refreshed version.
That's great, I have v2 almost ready, I'll send it tomorrow.
> Thanks,
> drew
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