[PATCH 2/2] jmpbuf: Add paddings for target specific usage

[H.J. Lu]

On Sat, Nov 25, 2017 at 8:34 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Nov 21, 2017 at 2:22 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Wed, Nov 15, 2017 at 5:20 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Wed, Nov 15, 2017 at 3:10 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>>> On 11/14/2017 02:10 PM, H.J. Lu wrote:
>>>>>
>>>>> +static int
>>>>> +do_test (void)
>>>>> +{
>>>>> +  sigjmp_buf sj;
>>>>> +  struct support_next_to_fault sigset_t_buf
>>>>> +    = support_next_to_fault_allocate (SIZEOF_SIGSET_T);
>>>>> +  sigset_t *m_p = (sigset_t *) sigset_t_buf.buffer;
>>>>> +  sigset_t m;
>>>>> +
>>>>> +  sigemptyset (&m);
>>>>> +  memcpy (m_p, &m, SIZEOF_SIGSET_T);
>>>>> +  sigprocmask (SIG_SETMASK, m_p, NULL);
>>>>> +  memcpy (&m, m_p, SIZEOF_SIGSET_T);
>>>>> +  if (sigsetjmp (sj, 0) == 0)
>>>>> +    {
>>>>> +      sigaddset (&m, SIGUSR1);
>>>>> +      memcpy (m_p, &m, SIZEOF_SIGSET_T);
>>>>> +      sigprocmask (SIG_SETMASK, m_p, NULL);
>>>>> +      memcpy (&m, m_p, SIZEOF_SIGSET_T);
>>>>> +      siglongjmp (sj, 1);
>>>>> +      return EXIT_FAILURE;
>>>>> +    }
>>>>> +  sigprocmask (SIG_SETMASK, NULL, m_p);
>>>>> +  memcpy (&m, m_p, SIZEOF_SIGSET_T);
>>>>> +  return sigismember (&m, SIGUSR1) ? EXIT_SUCCESS : EXIT_FAILURE;
>>>>> +}
>>>>
>>>>
>>>> Sorry, I don't understand anymore what this test is supposed to test and
>>>> how.
>>>
>>> This tests the reduced __jmp_buf_sigset_t used by __saved_mask is
>>> bigger than sigset expected by kernel.
>>>
>>>> To be honest, I don't like how you inject the internal definition of
>>>> jmp_buf.  Is this the way we do it for the nptl types?
>>>
>>> I only need to make some room in
>>>
>>> /* Calling environment, plus possibly a saved signal mask.  */
>>> struct __jmp_buf_tag
>>>   {
>>>     /* NOTE: The machine-dependent definitions of `__sigsetjmp'
>>>        assume that a `jmp_buf' begins with a `__jmp_buf' and that
>>>        `__mask_was_saved' follows it.  Do not move these members
>>>        or add others before it.  */
>>>     __jmp_buf __jmpbuf; /* Calling environment.  */
>>>     int __mask_was_saved; /* Saved the signal mask?  */
>>>     __sigset_t __saved_mask; /* Saved signal mask.  */
>>>   };
>>>
>>> for target specific purpose.   I changed it to
>>>
>>> struct __jmp_buf_tag
>>>   {
>>>     /* NOTE: The machine-dependent definitions of `__sigsetjmp'
>>>        assume that a `jmp_buf' begins with a `__jmp_buf' and that
>>>        `__mask_was_saved' follows it.  Do not move these members
>>>        or add others before it.  */
>>>     __jmp_buf __jmpbuf; /* Calling environment.  */
>>>     int __mask_was_saved; /* Saved the signal mask?  */
>>>     union
>>>     {
>>>     __sigset_t __saved_mask_compat;
>>>     struct
>>>       {
>>> __jmp_buf_sigset_t __saved_mask;
>>> /* Paddings for architecture specific usage.  */
>>> unsigned long int __padding[12];
>>>       } __saved;
>>>     }  __saved_mask;
>>>   };
>>>
>>> #define __saved_mask __saved_mask.__saved.__saved_mask
>>>
>>> I did only to  __sigset_t  in __jmp_buf_tag and this test verifies that the size
>>> of __jmp_buf_sigset_t works with sigprocmask.
>>>
>>> Are you suggesting we make some room in __sigset_t directly?  This will
>>> require very extensive changes. If not, what do you exactly suggest?
>>>
>>>> I think you should check _JUMP_BUF_SIGSET_NSIG against a kernel constant
>>>> (_NSIGS?) somewhere.
>>>
>>> There is a _Static_assert in include/setjmp.h.  But it isn't triggered.  This
>>> updated patch moves it to sysdeps/unix/sysv/linux/__saved_mask.h.   Now
>>> I got
>>>
>>> ../sysdeps/unix/sysv/linux/__saved_mask.h:32:1: error: static
>>> assertion failed: "size of ___saved_mask < size of
>>> __sigprocmask_sigset_t"
>>>  _Static_assert (sizeof (___saved_mask) >= sizeof (__sigprocmask_sigset_t),
>>>
>>> if __jmp_buf_sigset_t is too small.
>>>
>>> --
>>> H.J.
>>
>> Any comments, suggestions or objections?  The patch is at
>>
>> https://sourceware.org/ml/libc-alpha/2017-11/msg00510.html
>>
>
> This is the updated patch.  It limited the changes to Linux/x86.
> Any comments?
>

This is the patch I am checking in tomorrow.

Andrew, you can include <jmp_buf-ssp.h> to get
SHADOW_STACK_POINTER_OFFSET in jmp_buf.


-- 
H.J.
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