linux-kernel - Re: [RFC PATCH v1 15/28] riscv/mm: Implement map_shadow

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Date: Thu, 22 Feb 2024 13:33:10 +0000
From: Mark Brown <broonie@...nel.org>
To: Deepak Gupta <debug@...osinc.com>
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Subject: Re: [RFC PATCH v1 15/28] riscv/mm: Implement map_shadow_stack()
 syscall

On Wed, Feb 21, 2024 at 04:47:11PM -0800, Deepak Gupta wrote:
> On Tue, Feb 06, 2024 at 04:01:28PM +0000, Mark Brown wrote:

> > > +#define SHADOW_STACK_SET_TOKEN (1ULL << 0)     /* Set up a restore token in the shadow stack */

> > For arm64 I also added a SHADOW_STACK_SET_MARKER for adding a top of
> > stack marker, did you have any thoughts on that for RISC-V?  I think x86
> > were considering adding it too, it'd be good if we could get things
> > consistent.

> Please correct me on this. A token at the top which can't be consumed to restore
> but *just* purely as marker, right?

Yes, for arm64 we just leave a zero word (which can't be a valid token)
above the stack switch token, that does mean you can't exactly tell that
the top of stack marker is there unless there's also a stack switch
token below it.

> It's a good design basic with not a lot of cost.

> I think risc-v should be able to converge on that.

Great.

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