Re: [PATCH] fs/binfmt_elf: use ELF_ET_DYN_BASE for PIE (ET_DYN with INTERP) binaries

[H.J. Lu]

On Mon, Jan 31, 2022 at 10:18 PM Azat Khuzhin <a3at.mail@xxxxxxxxx> wrote:
>
> On Mon, Jan 31, 2022 at 01:30:38PM -0800, H.J. Lu wrote:
> > On Mon, Jan 31, 2022 at 12:17 PM Azat Khuzhin <a3at.mail@xxxxxxxxx> wrote:
> > >
> > > Since 9630f0d60fec ELF_ET_DYN_BASE is not used as a load_bias anymore
> > > and this breaks PIE binaries, since after this change data segment
> > > became too nearby the stack:
> > >
> > > Before 9630f0d60fec:
> > >
> > >     $ strace -febrk /tmp/test-stack |& head
> > >     brk(NULL)                               = 0x555555559000
> > >     $ /tmp/test-stack
> > >     bottom_of_stack = 0x7fffffffc5c0
> > >     recursion depth: 1 (stack diff: 32)
> > >     ...
> > >     recursion depth: 7690 (stack diff: 8365664)
> > >     Segmentation fault (core dumped)
> > >
> > > After 9630f0d60fec:
> > >
> > >     $ strace -ebrk /tmp/test-stack  |& head
> > >     brk(NULL)                               = 0x7ffff7fff000
> > >
> > >     $ /tmp/test-stack
> > >     bottom_of_stack = 0x7fffffffc640
> > >     recursion depth: 1 (stack diff: 32)
> > >     ...
> > >     recursion depth: 146 (stack diff: 157792)
> > >     Segmentation fault (core dumped)
> > >
> > > Found this during compiling with clang, that started to randomly
> > > SIGSEGV when it eats some heap.
> >
> > How do I reproduce it on x86-64?
>
> It fails for me for pretty big C++ unit, so I don't have a simple
> reproducer with clang, but the attached reproducer below should show the
> problem.

The reproducer doesn't fail for me under 5.17-rc2 on Fedora 35/x86-64
with 32GB RAM.  Did you turn off PF_RANDOMIZE?

> > > Reproducer:
> > >
> > >     #include <stdio.h>
> > >     #include <stddef.h>
> > >     #include <stdlib.h>
> > >
> > >     static int depth = 0;
> > >     static void* bottom_of_stack;
> > >
> > >     int inner()
> > >     {
> > >         char buffer[1024];
> > >         ptrdiff_t diff;
> > >         int ret;
> > >
> > >         ++depth;
> > >         diff = bottom_of_stack - __builtin_frame_address(0);
> > >
> > >         fprintf(stderr,
> > >                 "recursion depth: %i (stack diff: %zu)\n",
> > >                 depth, (size_t)diff);
> > >
> > >         for (size_t i = 0; i < 1024; ++i)
> > >                 ret += buffer[i];
> > >
> > >         ret += inner();
> > >
> > >         return ret;
> > >     }
> > >
> > >     int main()
> > >     {
> > >         for (size_t size = 0; size < 128<<20; size += 16<<10)
> > >                 malloc(16<<10);
> > >
> > >         bottom_of_stack = __builtin_frame_address(0);
> > >         fprintf(stderr, "bottom_of_stack = %p\n", bottom_of_stack);
> > >         inner();
> > >     }



-- 
H.J.