linux-kernel - Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory accounting

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Message-ID: <54f73dbb6a26641616e258857f3cf1275d99ef16.camel@intel.com>
Date:   Wed, 22 Feb 2023 00:06:10 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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CC:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v6 22/41] mm/mmap: Add shadow stack pages to memory
 accounting

On Tue, 2023-02-21 at 09:31 +0100, David Hildenbrand wrote:
> > > Why not modify is_stack_mapping() ?
> > 
> > It kind of sticks out a little in this conditional, but
> > is_stack_mapping() has this comment:
> > /*
> >    * Stack area - automatically grows in one direction
> >    *
> >    * VM_GROWSUP / VM_GROWSDOWN VMAs are always private anonymous:
> >    * do_mmap() forbids all other combinations.
> >    */
> > 
> > Shadow stack don't grow, so it doesn't quite fit. There used to be
> > an
> > is_shadow_stack_mapping(), but it was removed because all that was
> > needed (for the time being) was the simple bitwise AND:
> > 
> > 
https://lore.kernel.org/lkml/804adbac-61e6-0fd2-f726-5735fb290199@intel.com/
> 
> As there is only a single user of is_stack_mapping(), I'd simply
> have 
> adjusted the doc of is_stack_mapping() to include shadow stacks.

Ok, I'll update the comment and add it there.