Re: [PATCH] AArch64 pauth: Support backtrace in EL1 (kernel space)

[Koudai Iwahori <koudai@google.com>]

Hi Luis,

Got it, thank you!

On Tue, Oct 4, 2022 at 5:24 PM Luis Machado <luis.machado@arm.com> wrote:

> Hi,
>
> On 9/28/22 03:59, Koudai Iwahori via Gdb-patches wrote:
> > The way to remove the signature bits from the address depends on the
> > 55th bit of the address. If 55th bit is zero, the signature bits should
> > be all cleared. If the 55th bit is one, the signature bits should be all
> > set.
> > ---
> > I found very similar patches after fixing this issue:
> >    https://sourceware.org/pipermail/gdb-patches/2022-July/190507.html
> >    https://sourceware.org/pipermail/gdb-patches/2021-October/182859.html
> > If this issue will be fixed in the near future, I can wait for it
>
> Yes, it should be fixed by the first link above. It is pending approval
> from maintainers, which should
> hopefully happen soon.
>
> I also have an upcoming patch (that relies on the above patch) to support
> pauth for user-mode QEMU.
>
> See https://sourceware.org/bugzilla/show_bug.cgi?id=29421.
>
> >
> >   gdb/aarch64-tdep.c | 16 +++++++++++++++-
> >   1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> > index d0387044934..16d1e44e903 100644
> > --- a/gdb/aarch64-tdep.c
> > +++ b/gdb/aarch64-tdep.c
> > @@ -244,6 +244,20 @@ class instruction_reader : public
> abstract_instruction_reader
> >
> >   } // namespace
> >
> > +/* removes the pauth signature bits from the address. */
> > +
> > +static CORE_ADDR
> > +aarch64_remove_pauth_signature (CORE_ADDR addr, CORE_ADDR mask)
> > +{
> > +  /* 55th bit in address determines whether the address comes from the
> top
> > +     address range or the bottom address range. */
> > +  constexpr CORE_ADDR pauth_va_range_select_mask = CORE_ADDR(1) << 55;
> > +  if (addr & pauth_va_range_select_mask)
> > +    return addr | mask;
> > +  else
> > +    return addr & ~mask;
> > +}
> > +
> >   /* If address signing is enabled, mask off the signature bits from the
> link
> >      register, which is passed by value in ADDR, using the register
> values in
> >      THIS_FRAME.  */
> > @@ -258,7 +272,7 @@ aarch64_frame_unmask_lr (aarch64_gdbarch_tdep *tdep,
> >       {
> >         int cmask_num = AARCH64_PAUTH_CMASK_REGNUM
> (tdep->pauth_reg_base);
> >         CORE_ADDR cmask = frame_unwind_register_unsigned (this_frame,
> cmask_num);
> > -      addr = addr & ~cmask;
> > +      addr = aarch64_remove_pauth_signature(addr, cmask);
> >
> >         /* Record in the frame that the link register required
> unmasking.  */
> >         set_frame_previous_pc_masked (this_frame);
>
>