RE: [PATCH v5 23/39] mm: Don't allow write GUPs to shadow stack memory

[Schimpe, Christina]

> On Tue, 2023-01-24 at 17:26 +0100, David Hildenbrand wrote:
> > > > Isn't it possible to overwrite GOT pointers using the same vector?
> > > > So I think it's merely reflecting the status quo.
> > >
> > > There was some debate on this. /proc/self/mem can currently write
> > > through read-only memory which protects executable code. So should
> > > shadow stack get separate rules? Is ROP a worry when you can
> > > overwrite executable code?
> > >
> >
> > The question is, if there is reasonable debugging reason to keep it.
> > I
> > assume if a debugger would adjust the ordinary stack, it would have to
> > adjust the shadow stack as well (oh my ...). So it sounds reasonable
> > to have it in theory at least ... not sure when debugger would support
> > that, but maybe they already do.
> 
> GDB support for shadow stack is queued up for whenever the kernel
> interface settles. I believe it just uses ptrace, and not this proc.
> But yea ptrace poke will still need to use FOLL_FORCE and be able to write
> through shadow stacks.

Our patches for GDB use /proc/PID/mem to read/write shadow stack memory.  
However, I think it should be possible to change this to ptrace but GDB normally uses
/proc/PID/mem to read/write target memory.

Regards,
Christina
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