[PATCH v2 17/29] ARM: kernel: use relative phys-to-virt patch tables

[Ard Biesheuvel]

On 4 September 2017 at 19:03, Nicolas Pitre <nicolas.pitre at linaro.org> wrote:
> On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
>
>> Replace the contents of the __pv_table entries with relative references
>> so that we don't have to relocate them at runtime when running the KASLR
>> kernel. This ensures these quantities are invariant under runtime
>> relocation, which makes any cache maintenance after runtime relocation
>> unnecessary.
>>
>> Cc: Russell King <linux at armlinux.org.uk>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  arch/arm/include/asm/memory.h |  6 +++---
>>  arch/arm/kernel/head.S        | 21 ++++++++++----------
>>  2 files changed, 13 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
>> index 1f54e4e98c1e..47a984e3a244 100644
>> --- a/arch/arm/include/asm/memory.h
>> +++ b/arch/arm/include/asm/memory.h
>> @@ -195,7 +195,7 @@ extern const void *__pv_table_begin, *__pv_table_end;
>>       __asm__("@ __pv_stub\n"                         \
>>       "1:     " instr "       %0, %1, %2\n"           \
>>       "       .pushsection .pv_table,\"a\"\n"         \
>> -     "       .long   1b\n"                           \
>> +     "       .long   1b - .\n"                       \
>>       "       .popsection\n"                          \
>
> [...]
>
>> --- a/arch/arm/kernel/head.S
>> +++ b/arch/arm/kernel/head.S
>> @@ -612,22 +611,22 @@ __fixup_a_pv_table:
>>       orr     r6, r6, r7, lsl #12
>>       orr     r6, #0x4000
>>       b       2f
>> -1:   add     r7, r3
>> -     ldrh    ip, [r7, #2]
>> +1:   add     r7, r4
>> +     ldrh    ip, [r7, #-2]
>
> Please use "ldrh ip, [r7, #(-4 + 2)]" so the -4 offset is clearly
> spelled out. The #-2 gave me a pause of confusion.
>
>>  ARM_BE8(rev16        ip, ip)
>>       tst     ip, #0x4000
>>       and     ip, #0x8f00
>>       orrne   ip, r6  @ mask in offset bits 31-24
>>       orreq   ip, r0  @ mask in offset bits 7-0
>>  ARM_BE8(rev16        ip, ip)
>> -     strh    ip, [r7, #2]
>> +     strh    ip, [r7, #-2]
>
> Ditto here.
>
>>       bne     2f
>> -     ldrh    ip, [r7]
>> +     ldrh    ip, [r7, #-4]
>
> And to be clear, here I'd use "#(-4 + 0)" to be explicit.
>
>>  ARM_BE8(rev16        ip, ip)
>>       bic     ip, #0x20
>>       orr     ip, ip, r0, lsr #16
>>  ARM_BE8(rev16        ip, ip)
>> -     strh    ip, [r7]
>> +     strh    ip, [r7, #-4]
>
> And so here.
>

OK

>
> With that:
>
> Reviewed-by: Nicolas Pitre <nico at linaro.org>

Thanks.