[PATCH -stable] arm64: mm: don't write garbage into TTBR1_EL1 register

[Nicolas Dechesne]

On Sat, Feb 24, 2018 at 9:34 AM, Greg KH <gregkh at linuxfoundation.org> wrote:
> On Fri, Feb 23, 2018 at 06:29:02PM +0000, Ard Biesheuvel wrote:
>> Stable backport commit 173358a49173 ("arm64: kpti: Add ->enable callback
>> to remap swapper using nG mappings") of upstream commit f992b4dfd58b did
>> not survive the backporting process unscathed, and ends up writing garbage
>> into the TTBR1_EL1 register, rather than pointing it to the zero page to
>> disable translations. Fix that.
>>
>> Cc: <stable at vger.kernel.org> #v4.14
>> Reported-by: Nicolas Dechesne <nicolas.dechesne at linaro.org>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  arch/arm64/mm/proc.S | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Any reason why you didn't cc: the stable list, as this is a patch that
> is not needed in mainline, right?
>
>> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
>> index 08572f95bd8a..2b473ddeb7a3 100644
>> --- a/arch/arm64/mm/proc.S
>> +++ b/arch/arm64/mm/proc.S
>> @@ -155,7 +155,7 @@ ENDPROC(cpu_do_switch_mm)
>>
>>  .macro       __idmap_cpu_set_reserved_ttbr1, tmp1, tmp2
>>       adrp    \tmp1, empty_zero_page
>> -     msr     ttbr1_el1, \tmp2
>> +     msr     ttbr1_el1, \tmp1
>
> I don't understand why this isn't also needed in Linus's tree.  What
> commit there prevents this from being required?

in master this code is

.macro  __idmap_cpu_set_reserved_ttbr1, tmp1, tmp2
    adrp    \tmp1, empty_zero_page
    phys_to_ttbr \tmp2, \tmp1
    msr ttbr1_el1, \tmp2
    isb

which can also explain why the (non trivial) cherry-picked commit
ended up wrong.

this change in master came from

529c4b05a3cb arm64: handle 52-bit addresses in TTBR

which afaik, is not needed on stable


>
> thanks,
>
> greg k-h