[PATCH v2 2/5] arm64: efi: apply strict permissons for UEFI Runtime Services regions

[Ard Biesheuvel]

On 18 May 2016 at 02:40, Shanker Donthineni <shankerd at codeaurora.org> wrote:
> Hi Ard,
>
> This patch causing the kernel boot fail using the UEFI firmware on
> Qualcomm Technologies QDF2XXX server platforms.
>
> +       /* RW- */
> +       if (attr & EFI_MEMORY_XP || type != EFI_RUNTIME_SERVICES_CODE)
> +               return pgprot_val(PAGE_KERNEL);
> +
>
> Changing above condition from 'or' to 'and' fixed the problem.Are we
> missing something here or intentionally implemented this logic?

The logic is sound, I think. If you need execute permissions on a
non-code region with the XP bit set, there is something wrong in the
firmware, unless you are hitting this case for an MMIO region perhaps?
Could you share the kernel log with efi=debug enabled?

> At least
> we need some pr_warn here if UEFI firmware passes EFI_RUNTIME_SEVRICE_CODE
> region that has an attribute EFI_MEMORY_XP.
>

No. DXE_RUNTIME_DRIVER modules are implemented as PE/COFF binaries,
which are covered completely by EfiRuntimeServicesCode regions.
However, a PE/COFF image consists of .text and .data sections, which
require different permissions, so PE/COFF binaries are represented by
several memory map entries in the memory attributes table, all of
which have a code type, but differ in the permission bits.

>
>
> On 03/30/2016 11:38 AM, Ard Biesheuvel wrote:
>> Recent UEFI versions expose permission attributes for runtime services
>> memory regions, either in the UEFI memory map or in the separate memory
>> attributes table. This allows the kernel to map these regions with
>> stricter permissions, rather than the RWX permissions that are used by
>> default. So wire this up in our mapping routine.
>>
>> Note that in the absence of permission attributes, we still only map
>> regions of type EFI_RUNTIME_SERVICE_CODE with the executable bit set.
>> Also, we base the mapping attributes of EFI_MEMORY_MAPPED_IO on the
>> type directly rather than on the absence of the EFI_MEMORY_WB attribute.
>> This is more correct, but is also required for compatibility with the
>> upcoming support for the Memory Attributes Table, which only carries
>> permission attributes, not memory type attributes.
>>
>> Cc: Mark Rutland <mark.rutland at arm.com>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  arch/arm64/kernel/efi.c | 54 +++++++++++++++-----
>>  1 file changed, 40 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
>> index b6abc852f2a1..33a6da160a50 100644
>> --- a/arch/arm64/kernel/efi.c
>> +++ b/arch/arm64/kernel/efi.c
>> @@ -17,22 +17,48 @@
>>
>>  #include <asm/efi.h>
>>
>> -int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t
>> *md)
>> +/*
>> + * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
>> + * executable, everything else can be mapped with the XN bits
>> + * set. Also take the new (optional) RO/XP bits into account.
>> + */
>> +static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
>>  {
>> -     pteval_t prot_val;
>> +     u64 attr = md->attribute;
>> +     u32 type = md->type;
>>
>> -     /*
>> -      * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
>> -      * executable, everything else can be mapped with the XN bits
>> -      * set.
>> -      */
>> -     if ((md->attribute & EFI_MEMORY_WB) == 0)
>> -             prot_val = PROT_DEVICE_nGnRE;
>> -     else if (md->type == EFI_RUNTIME_SERVICES_CODE ||
>> -              !PAGE_ALIGNED(md->phys_addr))
>> -             prot_val = pgprot_val(PAGE_KERNEL_EXEC);
>> -     else
>> -             prot_val = pgprot_val(PAGE_KERNEL);
>> +     if (type == EFI_MEMORY_MAPPED_IO)
>> +             return PROT_DEVICE_nGnRE;
>> +
>> +     if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
>> +                   "UEFI Runtime regions are not aligned to 64 KB --
>> buggy firmware?"))
>> +             /*
>> +              * If the region is not aligned to the page size of the
>> OS, we
>> +              * can not use strict permissions, since that would also
>> affect
>> +              * the mapping attributes of the adjacent regions.
>> +              */
>> +             return pgprot_val(PAGE_KERNEL_EXEC);
>> +
>> +     /* R-- */
>> +     if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
>> +         (EFI_MEMORY_XP | EFI_MEMORY_RO))
>> +             return pgprot_val(PAGE_KERNEL_RO);
>> +
>> +     /* R-X */
>> +     if (attr & EFI_MEMORY_RO)
>> +             return pgprot_val(PAGE_KERNEL_ROX);
>> +
>> +     /* RW- */
>> +     if (attr & EFI_MEMORY_XP || type != EFI_RUNTIME_SERVICES_CODE)
>> +             return pgprot_val(PAGE_KERNEL);
>> +
>> +     /* RWX */
>> +     return pgprot_val(PAGE_KERNEL_EXEC);
>> +}
>> +
>> +int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t
>> *md)
>> +{
>> +     pteval_t prot_val = create_mapping_protection(md);
>>
>>       create_pgd_mapping(mm, md->phys_addr, md->virt_addr,
>>                          md->num_pages << EFI_PAGE_SHIFT,
>
> --
> Shanker Donthineni
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>