linux-kernel - Re: [RFC 7/9] arm64: expose PAC bit positions via ptrace

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Date:   Tue, 25 Jul 2017 15:59:04 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        arnd@...db.de, jiong.wang@....com, marc.zyngier@....com,
        catalin.marinas@....com, suzuki.poulose@....com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org
Subject: Re: [RFC 7/9] arm64: expose PAC bit positions via ptrace

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.
 */

> > 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.

Mark.