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SubjectRe: [RFC 7/9] arm64: expose PAC bit positions via ptrace
On Tue, Jul 25, 2017 at 03:59:04PM +0100, Mark Rutland wrote:
> On Tue, Jul 25, 2017 at 01:11:48PM +0100, Dave Martin wrote:
> > On Mon, Apr 03, 2017 at 04:19:23PM +0100, Mark Rutland wrote:
> > > +/*
> > > + * The pointer bits used by a pointer authentication code.
> > > + * If we were to use tagged pointers, bits 63:56 would also apply.
> > > + */
> > > +#define ptrauth_pac_mask() GENMASK(54, VA_BITS)
> >
> > Tagged pointers _are_ enabled for userspace by default, no?
>
> Yes; I'd meant s/tagged/untagged/.
>
> I've corrected this to:
>
> /*
> * The EL0 pointer bits used by a pointer authentication code.
> * This is dependent on TBI0 being enabled, or bits 63:56 would also apply.
> */

Yes, that's better. If we do enable untagged pointers for userspace at
some point though, this is likely to be missed.

I don't have a good answer to this.

> > > diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> > > index b59ee07..cae3d1e 100644
> > > --- a/include/uapi/linux/elf.h
> > > +++ b/include/uapi/linux/elf.h
> > > @@ -414,6 +414,7 @@
> > > #define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */
> > > #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */
> > > #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */
> > > +#define NT_ARM_PAC_MASK 0x405 /* ARM pointer authentication code masks */
> >
> > The is the value tentatively assigned to NT_ARM_SVE.
>
> I must've generated this patch before I corrected this; my local branch
> (and kernel.org) have 0x406 here.
>
> Sorry about that.

Shame, I had a rant about pragmatism prepped and ready ;)

Cheers
---Dave

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