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

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Message-ID: <CY4PR11MB2005CA3050147893EAC10B9EF9CE9@CY4PR11MB2005.namprd11.prod.outlook.com>
Date:   Wed, 25 Jan 2023 15:36:02 +0000
From:   "Schimpe, Christina" <christina.schimpe@...el.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "david@...hat.com" <david@...hat.com>
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Subject: RE: [PATCH v5 23/39] mm: Don't allow write GUPs to shadow stack
 memory

> 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
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
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