linux-kernel - Re: [PATCH v3 21/36] arm64/mm: Implement map_shadow

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Date:   Fri, 4 Aug 2023 16:43:45 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "broonie@...nel.org" <broonie@...nel.org>
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Subject: Re: [PATCH v3 21/36] arm64/mm: Implement map_shadow_stack()

On Fri, 2023-08-04 at 14:38 +0100, Mark Brown wrote:
> On Wed, Aug 02, 2023 at 05:27:54PM +0100, Mark Brown wrote:
> > On Tue, Aug 01, 2023 at 08:57:59PM +0000, Edgecombe, Rick P wrote:
> 
> > > To make sure we are on the same page: What I'm saying is say we
> > > do
> > > something like add another flag SHADOW_STACK_SET_MARKER that
> > > means add
> > > a marker at the end (making the token off by one frame). Then you
> > > can
> > > just reject any flags != (SHADOW_STACK_SET_MARKER |
> > > SHADOW_STACK_SET_TOKEN) value, and leave the rest of the code as
> > > is. So
> > > not really implementing anything new. 
> 
> > > Then x86 could use the same flag meanings if/when it implements
> > > end
> > > markers. If it doesn't seem worth it, it's not a big deal on my
> > > end.
> > > Just seemed that they were needlessly diverging.
> 
> > Yes, my understanding of the flags is the same.  I'll definitely
> > implement omitting the cap since there's an actual use case for
> > that
> > (extending an existing stack, it's marginally safer to not have any
> > opportunity to pivot into the newly allocated region).
> 
> BTW are you planning to repost the series for this release?  We're
> almost at -rc5 which is pretty late and I didn't see anything yet. 

There were a few patches I posted on top of the last series after your
comments, but I wasn't planning on reposting the whole thing. Why do
you ask? Just trying to figure out the best version to base off of?

> It
> looks like there's a branch in tip that's getting some updates but
> it's
> not getting merged for -next.

Hmm, not sure why it's not in -next anymore. I'll look into that.
Thanks for pointing it out.