Subject: [PATCH v2] arm64: kaslr: Fix up the kernel image alignment

From: [email-masked] (Srinivas Ramana)
Date: Thu, 23 Mar 2017 15:02:49 +0530

On 03/22/2017 07:15 PM, Srinivas Ramana wrote:
> On 03/22/2017 06:10 PM, Will Deacon wrote:
>> On Wed, Mar 22, 2017 at 12:16:24PM +0000, Ard Biesheuvel wrote:
>>> On 22 March 2017 at 11:38, Srinivas Ramana <[email-masked]>
>>> wrote:
>>>> From: Neeraj Upadhyay <[email-masked]>
>>>>
>>>> If kernel image extends across alignment boundary, existing
>>>> code increases the KASLR offset by size of kernel image. The
>>>> offset is masked after resizing. There are cases, where after
>>>> masking, we may still have kernel image extending across
>>>> boundary. This eventually results in only 2MB block getting
>>>> mapped while creating the page tables. This results in data aborts
>>>> while accessing unmapped regions during second relocation (with
>>>> kaslr offset) in __primary_switch. To fix this problem, round up the
>>>> kernel image size, by swapper block size, before adding it for
>>>> correction.
>>>>
>>>> For example consider below case, where kernel image still crosses
>>>> 1GB alignment boundary, after masking the offset, which is fixed
>>>> by rounding up kernel image size.
>>>>
>>>> SWAPPER_TABLE_SHIFT = 30
>>>> Swapper using section maps with section size 2MB.
>>>> CONFIG_PGTABLE_LEVELS = 3
>>>> VA_BITS = 39
>>>>
>>>> _text  : 0xffffff8008080000
>>>> _end   : 0xffffff800aa1b000
>>>> offset : 0x1f35600000
>>>> mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1)
>>>>
>>>> (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
>>>> (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
>>>>
>>>> offset after existing correction (before mask) = 0x1f37f9b000
>>>> (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
>>>> (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
>>>>
>>>> offset (after mask) = 0x1f37e00000
>>>> (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
>>>> (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
>>>>
>>>> new offset w/ rounding up = 0x1f38000000
>>>> (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
>>>> (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
>>>>
>>>> Fixes: f80fb3a3d508 ("arm64: add support for kernel ASLR")
>>>> Signed-off-by: Neeraj Upadhyay <[email-masked]>
>>>> Signed-off-by: Srinivas Ramana <[email-masked]>
>>>
>>> Reviewed-by: Ard Biesheuvel <[email-masked]>
>>>
>>> ... and thanks for the excellent commit log message!
>>
>> Thanks both. I've picked this up as a fix.
>>
>> Will
>>
>
> Thanks Ard and Will for the review and picking this patch.
> can we also CC: <[email-masked]> ?
>
> Thanks,
> -- Srinivas R
>
>

Sorry, there is a checkpatch error in the last patch. I will submit v3
after fixing the checkpatch error.

Thanks,
-- Srinivas R

-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, 
Inc.,
is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.