Re: [PATCH 1/2] arm64/efi: base UEFI mapping permissions on region attributes

[Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 30 June 2015 at 16:50, Mark Salter <msalter-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> On Tue, 2015-06-30 at 12:17 +0200, Ard Biesheuvel wrote:
>
>> Currently, we infer the UEFI memory region mapping permissions
>> from the memory region type (i.e., runtime services code are
>> mapped RWX and runtime services data mapped RW-). This appears to
>> work fine but is not entirely UEFI spec compliant. So instead, use
>> the designated permission attributes to decide how these regions
>> should be mapped.
>>
>> Since UEFIv2.5 introduces a new EFI_MEMORY_RO permission attribute,
>> and redefines EFI_MEMORY_WP as a cacheability attribute, use only
>> the former as a read-only attribute. For setting the PXN bit, the
>> corresponding EFI_MEMORY_XP attribute is used.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>> ---
>>  arch/arm64/kernel/efi.c | 32 +++++++++++++-------
>>  1 file changed, 21 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
>> index ab21e0d58278..5dcab58d5d30 100644
>> --- a/arch/arm64/kernel/efi.c
>> +++ b/arch/arm64/kernel/efi.c
>> @@ -247,20 +247,30 @@ static bool __init efi_virtmap_init(void)
>>               memrange_efi_to_native(&paddr, &npages);
>>               size = npages << PAGE_SHIFT;
>>
>> -             pr_info("  EFI remap 0x%016llx => %p\n",
>> -                     md->phys_addr, (void *)md->virt_addr);
>> -
>> -             /*
>> -              * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
>> -              * executable, everything else can be mapped with the XN bits
>> -              * set.
>> -              */
>>               if (!is_normal_ram(md))
>>                       prot = __pgprot(PROT_DEVICE_nGnRE);
>> -             else if (md->type == EFI_RUNTIME_SERVICES_CODE)
>> -                     prot = PAGE_KERNEL_EXEC;
>>               else
>> -                     prot = PAGE_KERNEL;
>> +                     prot = PAGE_KERNEL_EXEC;
>> +
>> +             /*
>> +              * On 64 KB granule kernels, only use strict permissions when
>> +              * the region does not share a 64 KB page frame with another
>> +              * region at either end.
>> +              */
>> +             if (!IS_ENABLED(CONFIG_ARM64_64K_PAGES) ||
>> +                 !(md->virt_addr % PAGE_SIZE ||
>> +                   (md->phys_addr + md->num_pages * EFI_PAGE_SIZE) % PAGE_SIZE)) {
>
> I think this would read easier with:
>
>                     (PAGE_ALIGNED(md->virt_addr) &&
>                       PAGE_ALIGNED(md->phys_addr + md->num_pages * EFI_PAGE_SIZE))) {
>

Yes, good point, I will change that.

>> +
>> +                     if (md->attribute & EFI_MEMORY_RO)
>> +                             prot |= __pgprot(PTE_RDONLY);
>> +                     if (md->attribute & EFI_MEMORY_XP)
>> +                             prot |= __pgprot(PTE_PXN);
>> +             }
>> +
>> +             pr_info("  EFI remap 0x%016llx => %p (R%c%c)\n",
>> +                     md->phys_addr, (void *)md->virt_addr,
>> +                     prot & __pgprot(PTE_RDONLY) ? '-' : 'W',
>> +                     prot & __pgprot(PTE_PXN) ? '-' : 'X');
>
> You can't maninulate pgprot_t directly like that. It will
> break STRICT_MM_TYPECHECKS. You need to use __pgprot_modify()
> and/or pgprot_val().
>
> arch/arm64/kernel/efi.c: In function ‘efi_virtmap_init’:
> arch/arm64/kernel/efi.c:266:10: error: invalid operands to binary | (have ‘pgprot_t’ and ‘pgprot_t’)
>      prot |= __pgprot(PTE_RDONLY);
>           ^
>    ...
>
> (In trying that, I see there are a number of other places which
> need some STRICT_MM_TYPECHECKS fixing)
>

Actually, I had 'prot |= PTE_RDONLY' but then changed it to the above
thinking that it would pass the strict type checks, but apparently not
:-)

I will fix that up as well.

Thanks,
Ard.


>>
>>               create_pgd_mapping(&efi_mm, paddr, md->virt_addr, size, prot);
>>       }
>