[PATCH v2 0/7] arm64: relax Image placement rules

[Ard Biesheuvel]

On 25 September 2015 at 01:44, Suzuki K. Poulose <Suzuki.Poulose at arm.com> wrote:
> On 25/09/15 00:19, Ard Biesheuvel wrote:
>>
>> On 24 September 2015 at 09:38, Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> wrote:
>>>
>>> On 24 September 2015 at 09:37, Suzuki K. Poulose <Suzuki.Poulose at arm.com>
>>> wrote:
>>>>
>>>> On 23/09/15 01:37, Ard Biesheuvel wrote:
>
>
>
>>>>
>>>> Ard,
>>>>
>>>> I gave your series a quick run and dumping the kernel page tables(with
>>>> CONFIG_ARM64_PTDUMP)
>>>> I find this problem :
>>>>
>>>> ...
>>>>
>>>> ---[ Kernel Mapping ]---
>>>> 0xffffffbffc000000-0xffffffbffc600000           6M     RW x  SHD AF
>>>> MEM/NORMAL    *****
>>>> 0xffffffbffc600000-0xffffffbffc7f5000        2004K     RW x  SHD AF
>>>> UXN
>>>> MEM/NORMAL
>>>> 0xffffffbffc7f5000-0xffffffbffc875000         512K     RW NX SHD AF
>>>> UXN
>>>> MEM/NORMAL
>>>> 0xffffffbffc875000-0xffffffbffca00000        1580K     RW x  SHD AF
>>>> UXN
>>>> MEM/NORMAL
>>>> ---[ Linear Mapping ]---
>>>> 0xffffffc000000000-0xffffffc040000000           1G     RW NX SHD AF
>>>> UXN
>>>> MEM/NORMAL
>>>>
>>>>
>>>> Note that the first mapping in the kernel doesn't have UXN set, which is
>>>> a
>>>> regression.
>>>> I haven't started digging into it yet, but I thought I will point it out
>>>> here, in case you
>>>> already fixed it.
>>>>
>>>
>>> Ok, thanks for pointing that out. I will look into it.
>>>
>>
>> Turns out that, since the kernel mapping is not overwritten by the
>> linear mapping, it retains the original permissions assigned in
>> head.S. So this is enough to fix it
>>
>> """
>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>> index 2df4a55f00d4..fcd250cff4bf 100644
>> --- a/arch/arm64/kernel/head.S
>> +++ b/arch/arm64/kernel/head.S
>> @@ -62,8 +62,8 @@
>>   /*
>>    * Initial memory map attributes.
>>    */
>> -#define PTE_FLAGS      PTE_TYPE_PAGE | PTE_AF | PTE_SHARED
>> -#define PMD_FLAGS      PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S
>> +#define PTE_FLAGS      PTE_TYPE_PAGE | PTE_AF | PTE_SHARED | PTE_UXN
>> +#define PMD_FLAGS      PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S |
>> PMD_SECT_UXN
>>
>>   #ifdef CONFIG_ARM64_64K_PAGES
>>   #define MM_MMUFLAGS    PTE_ATTRINDX(MT_NORMAL) | PTE_FLAGS
>> """
>>
>
> Yes, that fixes it. With that I get :
>
> ---[ Kernel Mapping ]---
> 0xffffffbffc000000-0xffffffbffc600000           6M     RW x  SHD AF    UXN
> MEM/NORMAL
> 0xffffffbffc600000-0xffffffbffc7f5000        2004K     RW x  SHD AF    UXN
> MEM/NORMAL
> 0xffffffbffc7f5000-0xffffffbffc875000         512K     RW NX SHD AF    UXN
> MEM/NORMAL
> 0xffffffbffc875000-0xffffffbffca00000        1580K     RW x  SHD AF    UXN
> MEM/NORMAL
> ---[ Linear Mapping ]---
> 0xffffffc000000000-0xffffffc080000000           2G     RW NX SHD AF    UXN
> MEM/NORMAL
> 0xffffffc800000000-0xffffffc880000000           2G     RW NX SHD AF    UXN
> MEM/NORMAL
>

Thanks.

Can I take that as a Tested-by ? :-)

>
>
>>
>>>> Note: I see that you have used CONFIG_ARM64_64K_PAGES to handle
>>>> section/table mapping
>>>> (which I have tried to cleanup in 16K page size series and which is not
>>>> merged yet).
>>>> We should be careful when we merge our patches, as we could miss such
>>>> new
>>>> cases.
>>>>
>>>
>>> I was aware of this, and I think it makes sense to the 16 KB pages to
>>> be merged first, and then I will rebase these patches on top of it.
>>>
>>
>> Do you have a git tree with the latest version?
>>
>
> Yes, it is available here :
>
> git://linux-arm.org/linux-skp.git  16k/v2-4.3-rc1
>

I rebased it, and the required changes are only minor.

I will post the rebased version once your changes have been merged.

-- 
Ard.