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

[Sergei Trofimovich <slyfox at gentoo dot org>]

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 :)

-- 

  Sergei

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