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

[Azat Khuzhin]

On Tue, Feb 01, 2022 at 05:15:38AM -0800, H.J. Lu wrote:
> 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?

Oh, yep, forgot to mention that I have kernel.randomize_va_space=0.