Re: [PATCH] arm64: vdso: Fix ABI regression in compat vdso

Vincenzo Frascino
2019-07-10T13:42:59Z

On 10/07/2019 14:25, Will Deacon wrote:
> On Wed, Jul 10, 2019 at 02:04:52PM +0100, Vincenzo Frascino wrote:
>> Prior to the introduction of Unified vDSO support and compat layer for
>> vDSO on arm64, AT_SYSINFO_EHDR was not defined for compat tasks.
>> In the current implementation, AT_SYSINFO_EHDR is defined even if the
>> compat vdso layer is not built and this causes a regression in the
>> expected behavior of the ABI.
>>
>> Restore the ABI behavior making sure that AT_SYSINFO_EHDR for compat
>> tasks is defined only when CONFIG_GENERIC_COMPAT_VDSO and
>> CONFIG_COMPAT_VDSO are enabled.
>
> I think you could do a better job in the changelog of explaining what's
> actually going on here. The problem seems to be that you're advertising
> the presence of a non-existent vDSO to userspace.
>
>> Reported-by: John Stultz <john.stultz@linaro.org>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>> ---
>> arch/arm64/include/asm/elf.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
>> index 3c7037c6ba9b..b7992bb9d414 100644
>> --- a/arch/arm64/include/asm/elf.h
>> +++ b/arch/arm64/include/asm/elf.h
>> @@ -202,7 +202,7 @@ typedef compat_elf_greg_t compat_elf_gregset_t[COMPAT_ELF_NGREG];
>> ({ \
>> set_thread_flag(TIF_32BIT); \
>> })
>> -#ifdef CONFIG_GENERIC_COMPAT_VDSO
>> +#if defined(CONFIG_COMPAT_VDSO) && defined(CONFIG_GENERIC_COMPAT_VDSO)
>
> Can't this just be #ifdef CONFIG_COMPAT_VDSO ?
>

Yes, I realized it after I pushed the patch that CONFIG_GENERIC_COMPAT_VDSO can
be removed. Posting v2 shortly.

> John -- can you give this a whirl, please?
>
> Cheers,
>
> Will
>

--
Regards,
Vincenzo