Re: git: 706f4a81a812 - main - exec: Introduce the PROC_PS_STRINGS() macro

On Tue, Jan 18, 2022 at 07:31:47AM -0800, John Baldwin wrote:
> On 1/17/22 1:13 PM, Mark Johnston wrote:
> > The branch main has been updated by markj:
> > 
> > URL: https://cgit.FreeBSD.org/src/commit/?id=706f4a81a81250a326ea25914e7effe1768f1a37
> > 
> > commit 706f4a81a81250a326ea25914e7effe1768f1a37
> > Author:     Mark Johnston <markj@FreeBSD.org>
> > AuthorDate: 2022-01-17 16:42:28 +0000
> > Commit:     Mark Johnston <markj@FreeBSD.org>
> > CommitDate: 2022-01-17 21:11:54 +0000
> > 
> >      exec: Introduce the PROC_PS_STRINGS() macro
> >      
> >      Rather than fetching the ps_strings address directly from a process'
> >      sysentvec, use this macro.  With stack address randomization the
> >      ps_strings address is no longer fixed.
> >      
> >      Reviewed by:    kib
> >      MFC after:      2 weeks
> >      Sponsored by:   The FreeBSD Foundation
> >      Differential Revision:  https://reviews.freebsd.org/D33704
> 
> FWIW, in CheriBSD we have a 'p_psstrings' member in struct proc that is a pointer
> to the ps_strings structure in user space that is set by the ABI during exec.

I did the exact same thing in an earlier version of the patch.  It ended
up being more useful to keep the stacktop address, and to derive the
ps_strings address from that.  I would like to MFC this as well, and
that'll be easier without having modified the layout of struct proc.

> CHERI removes the need for ASLR, but due to alignment requirements of capabilities
> the stack is not a fixed location as its address can vary based on the size.

Is it possible to use PROC_PS_STRINGS() there?