Re: [PATCH] compat: Fix endian issue in union sigval

From: Bamvor Jian Zhang
Date: Tue Feb 17 2015 - 02:23:08 EST

On 2015/2/13 18:44, Catalin Marinas wrote:
> On Fri, Feb 13, 2015 at 04:00:43PM +0800, Bamvor Jian Zhang wrote:
>> On 2015/2/11 23:40, Catalin Marinas wrote:
>>> On Wed, Feb 11, 2015 at 07:22:08PM +0800, Bamvor Jian Zhang wrote:
>>>> On 2015/2/10 20:27, Catalin Marinas wrote:
>>>>> On Tue, Feb 10, 2015 at 10:10:11AM +0000, Zhang Jian(Bamvor) wrote:
>> ...
>>> The native sigval_t is also a union but on 64-bit big endian, the
>>> sival_int overlaps with the most significant 32-bit of the sival_ptr.
>>> So reading sival_int would always be 0. When the compat siginfo is
>>> copied to user, arm64 reads the native sival_ptr (si_ptr) and converts
>>> it to the compat one, getting the correct 32-bit value. However, other
>>> architectures access sival_int (si_int) instead which breaks with your
>>> get_compat_sigevent() changes.
>>>>> I think the correct fix is in the arm64 code:
>>>> The following code could fix my issue.
>>> Without any parts of your patch?
>> Yes. As you mentioned above, sival_int overlaps the most significant 32bit
>> of the sival_ptr, it seems that your patch is right if sival_ptr is less than
>> 32bit.
> I don't follow you here. sival_ptr is greater than 32-bit on a 64-bit
> kernel.
Sorry for confuse. I was considering if the pointer in sival_ptr is greater
than 32bit in 64bit application. But it seems that it is not relative to my
issue: We only talk about the 32bit application here.
>>> I think that's correct fix since in the SIGEV_THREAD mq_notify case, we
>>> would not deliver a signal as notification, so the sival_int value is
>>> irrelevant (it would be 0 for big-endian compat tasks because of the
>>> sigval_t union on 64-bit).
>>> Your patch would work as well but you have to change all the other
>>> architectures to use si_ptr when copying to a compat siginfo.
>> Yeah, it seems that my patch is useful only if the sival_ptr is bigger
>> than 32bit. It need the similar changes with following catalin's patch
>> in the following 64bit architecture:
>> x86: arch/x86/ia32/ia32_signal.c
> That's a little endian architecture and the use of ptr_to_compat() looks
> fine to me.
>> tile, s390: arch/xxx/kernel/compat_signal.c
> s390 uses si_int already, as in my proposed arm64 patch.
> tile seems to be bi-endian, though I couldn't see a Kconfig option, nor
> something defining __BIG_ENDIAN__ in headers or Makefile. I guess it's
> coming from the compiler directly. Anyway, on big endian tile, I we have
> the same issue as on big endian arm64.
>> parisc, sparc, mips: arch/xxx/kernel/signal32.c
> paris, sparc and mips all use si_int instead of si_ptr, so that's fine.
>> powerpc: arch/xxx/kernel/signal_32.c
> Same for powerpc, it uses si_int instead of si_ptr.
>> cc these maintainers for input.
> I think it's only tile that needs fixing for big endian, something like
> the arm64 patch below:
Agree. I was thinking if it is not very clear that app write to si_ptr in
userspace while kernel only read/write si_int.



>>>>> diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
>>>>> index e299de396e9b..32601939a3c8 100644
>>>>> --- a/arch/arm64/kernel/signal32.c
>>>>> +++ b/arch/arm64/kernel/signal32.c
>>>>> @@ -154,8 +154,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
>>>>> case __SI_TIMER:
>>>>> err |= __put_user(from->si_tid, &to->si_tid);
>>>>> err |= __put_user(from->si_overrun, &to->si_overrun);
>>>>> - err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr,
>>>>> - &to->si_ptr);
>>>>> + err |= __put_user(from->si_int, &to->si_int);
>>>>> break;
>>>>> case __SI_POLL:
>>>>> err |= __put_user(from->si_band, &to->si_band);
>>>>> @@ -184,7 +183,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
>>>>> case __SI_MESGQ: /* But this is */
>>>>> err |= __put_user(from->si_pid, &to->si_pid);
>>>>> err |= __put_user(from->si_uid, &to->si_uid);
>>>>> - err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, &to->si_ptr);
>>>>> + err |= __put_user(from->si_int, &to->si_int);
>>>>> break;
>>>>> case __SI_SYS:
>>>>> err |= __put_user((compat_uptr_t)(unsigned long)

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