Re: [PATCH][BZ 21672] fix pthread_create crash in ia64

[Sergei Trofimovich <slyfox at gentoo dot org>]

On Wed, 5 Jul 2017 22:47:17 +0100
Sergei Trofimovich <slyfox@gentoo.org> wrote:

> On Sun, 25 Jun 2017 23:07:15 +0100
> Sergei Trofimovich <slyfox@gentoo.org> wrote:
> 
> > Minimal reproducer:
> > 
> >     #include <pthread.h>
> > 
> >     static void * f (void * p) { return NULL; }
> > 
> >     int main (int argc, const char ** argv) {
> >         pthread_t t;
> >         pthread_create (&t, NULL, &f, NULL);
> > 
> >         pthread_join (t, NULL);
> >         return 0;
> >     }
> > 
> >     $ gcc -O0 -ggdb3 -o r bug.c -pthread && ./r
> > 
> >     Program terminated with signal SIGSEGV, Segmentation fault.
> >     #0  0x2000000000077da0 in start_thread (arg=0x0) at pthread_create.c:432
> >     432         __madvise (pd->stackblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> > 
> > Here crash happens right after attempt to free unused part of
> > thread's stack.
> > 
> > On most architectures stack grows only down or grows only up.
> > And there glibc decides which of unused ends of stack blocks can be freed.
> > 
> > ia64 maintans two stacks. Both of them grow from the opposite directions:
> >  - normal "sp" stack (stack for local variables) grows down
> >  - register stack "bsp" grows up from the opposite end of stack block
> > 
> > In this failure case we have prematurely freed "rsp" stack.
> > 
> > The change leaves a few pages from both sides of stack block.
> > 
> > Bug: https://sourceware.org/PR21672
> > Bug: https://bugs.gentoo.org/622694
> > Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> > ---
> >  nptl/pthread_create.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
> > index 7a970ffc5b..6e3f6db5b1 100644
> > --- a/nptl/pthread_create.c
> > +++ b/nptl/pthread_create.c
> > @@ -555,10 +555,24 @@ START_THREAD_DEFN
> >    size_t pagesize_m1 = __getpagesize () - 1;
> >  #ifdef _STACK_GROWS_DOWN
> >    char *sp = CURRENT_STACK_FRAME;
> > -  size_t freesize = (sp - (char *) pd->stackblock) & ~pagesize_m1;
> > +  char *freeblock = (char *) pd->stackblock;
> > +  size_t freesize = (sp - freeblock) & ~pagesize_m1;
> >    assert (freesize < pd->stackblock_size);
> > +# ifdef __ia64__
> >    if (freesize > PTHREAD_STACK_MIN)
> > -    __madvise (pd->stackblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> > +    {
> > +      /* On ia64 stack grows both ways!
> > +         - normal "sp" stack (stack for local variables) grows down
> > +         - register stack "bsp" grows up from the opposite end of stack block
> > +
> > +         Thus we leave PTHREAD_STACK_MIN bytes from stack block top
> > +         and leave same PTHREAD_STACK_MIN at stack block bottom.  */
> > +      freeblock += PTHREAD_STACK_MIN;
> > +      freesize -= PTHREAD_STACK_MIN;
> > +    }
> > +# endif
> > +  if (freesize > PTHREAD_STACK_MIN)
> > +    __madvise (freeblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> >  #else
> >    /* Page aligned start of memory to free (higher than or equal
> >       to current sp plus the minimum stack size).  */
> > -- 
> > 2.13.1
> >   
> 
> Ping :)

Ping^2

-- 

  Sergei

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