Re: git: 21e45c30c35c - main - mmap(MAP_STACK): on stack grow, use original protection

In message <20230720163231.B1D4277@slippy.cwsent.com>, Cy Schubert writes:
> In message <202307201412.36KECDSU084918@gitrepo.freebsd.org>, Konstantin 
> Belous
> ov writes:
> > The branch main has been updated by kib:
> >
> > URL: https://cgit.FreeBSD.org/src/commit/?id=21e45c30c35c9aa732073f725924ca
> f5
> > 81c93460
> >
> > commit 21e45c30c35c9aa732073f725924caf581c93460
> > Author:     Konstantin Belousov <kib@FreeBSD.org>
> > AuthorDate: 2023-07-19 11:05:32 +0000
> > Commit:     Konstantin Belousov <kib@FreeBSD.org>
> > CommitDate: 2023-07-20 14:11:42 +0000
> >
> >     mmap(MAP_STACK): on stack grow, use original protection
> >     
> >     If mprotect(2) changed protection in the bottom of the currently grown
> >     stack region, currently the changed protection would be used for the
> >     stack grow on next fault.  This is arguably unexpected.
> >     
> >     Store the original protection for the entry at mmap(2) time in the
> >     offset member of the gap vm_map_entry, and use it for protection of the
> >     grown stack region.
> >     
> >     PR:     272585
> >     Reported by:    John F. Carr <jfc@mit.edu>
> >     Reviewed by:    alc, markj
> >     Sponsored by:   The FreeBSD Foundation
> >     MFC after:      1 week
> >     Differential revision:  https://reviews.freebsd.org/D41089
> > ---
> >  sys/vm/vm_map.c | 24 ++++++++++++++++--------
> >  sys/vm/vm_map.h |  4 ++++
> >  2 files changed, 20 insertions(+), 8 deletions(-)
> >
> > diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
> > index a02107b5e64d..997a49111a59 100644
> > --- a/sys/vm/vm_map.c
> > +++ b/sys/vm/vm_map.c
> > @@ -4493,7 +4493,7 @@ static int
> >  vm_map_stack_locked(vm_map_t map, vm_offset_t addrbos, vm_size_t max_ssize
> ,
> >      vm_size_t growsize, vm_prot_t prot, vm_prot_t max, int cow)
> >  {
> > -	vm_map_entry_t new_entry, prev_entry;
> > +	vm_map_entry_t gap_entry, new_entry, prev_entry;
> >  	vm_offset_t bot, gap_bot, gap_top, top;
> >  	vm_size_t init_ssize, sgp;
> >  	int orient, rv;
> > @@ -4575,11 +4575,14 @@ vm_map_stack_locked(vm_map_t map, vm_offset_t addrb
> os
> > , vm_size_t max_ssize,
> >  		 * read-ahead logic is never used for it.  Re-use
> >  		 * next_read of the gap entry to store
> >  		 * stack_guard_page for vm_map_growstack().
> > +		 * Similarly, since a gap cannot have a backing object,
> > +		 * store the original stack protections in the
> > +		 * object offset.
> >  		 */
> > -		if (orient == MAP_STACK_GROWS_DOWN)
> > -			vm_map_entry_pred(new_entry)->next_read = sgp;
> > -		else
> > -			vm_map_entry_succ(new_entry)->next_read = sgp;
> > +		gap_entry = orient == MAP_STACK_GROWS_DOWN ?
> > +		    vm_map_entry_pred(new_entry) : vm_map_entry_succ(new_entry)
> > ;
> > +		gap_entry->next_read = sgp;
> > +		gap_entry->offset = prot;
> >  	} else {
> >  		(void)vm_map_delete(map, bot, top);
> >  	}
> > @@ -4599,6 +4602,7 @@ vm_map_growstack(vm_map_t map, vm_offset_t addr, vm_m
> ap
> > _entry_t gap_entry)
> >  	struct ucred *cred;
> >  	vm_offset_t gap_end, gap_start, grow_start;
> >  	vm_size_t grow_amount, guard, max_grow;
> > +	vm_prot_t prot;
> >  	rlim_t lmemlim, stacklim, vmemlim;
> >  	int rv, rv1 __diagused;
> >  	bool gap_deleted, grow_down, is_procstack;
> > @@ -4739,6 +4743,12 @@ retry:
> >  	}
> >  
> >  	if (grow_down) {
> > +		/*
> > +		 * The gap_entry "offset" field is overloaded.  See
> > +		 * vm_map_stack_locked().
> > +		 */
> > +		prot = gap_entry->offset;
> > +
> >  		grow_start = gap_entry->end - grow_amount;
> >  		if (gap_entry->start + grow_amount == gap_entry->end) {
> >  			gap_start = gap_entry->start;
> > @@ -4751,9 +4761,7 @@ retry:
> >  			gap_deleted = false;
> >  		}
> >  		rv = vm_map_insert(map, NULL, 0, grow_start,
> > -		    grow_start + grow_amount,
> > -		    stack_entry->protection, stack_entry->max_protection,
> > -		    MAP_STACK_GROWS_DOWN);
> > +		    grow_start + grow_amount, prot, prot, MAP_STACK_GROWS_DOWN)
> > ;
> >  		if (rv != KERN_SUCCESS) {
> >  			if (gap_deleted) {
> >  				rv1 = vm_map_insert(map, NULL, 0, gap_start,
> > diff --git a/sys/vm/vm_map.h b/sys/vm/vm_map.h
> > index fd8b606e8ddc..c4ed36ce57ba 100644
> > --- a/sys/vm/vm_map.h
> > +++ b/sys/vm/vm_map.h
> > @@ -97,6 +97,10 @@ union vm_map_object {
> >   *	a VM object (or sharing map) and offset into that object,
> >   *	and user-exported inheritance and protection information.
> >   *	Also included is control information for virtual copy operations.
> > + *
> > + *	For stack gap map entries (MAP_ENTRY_GUARD | MAP_ENTRY_GROWS_DOWN
> > + *	or UP), the next_read member is reused as the stack_guard_page
> > + *	storage, and offset is the stack protection.
> >   */
> >  struct vm_map_entry {
> >  	struct vm_map_entry *left;	/* left child or previous entry */
> >
>
> This commit has caused screen (sysutils/screen) to display the following 
> error when opening a new screen window (ctrl-A c):
>
> pid 28473 comm screen-4.9.0 has trashed its stack, killing
>
>
> -- 
> Cheers,
> Cy Schubert <Cy.Schubert@cschubert.com>
> FreeBSD UNIX:  <cy@FreeBSD.org>   Web:  https://FreeBSD.org
> NTP:           <cy@nwtime.org>    Web:  https://nwtime.org
>
> 			e^(i*pi)+1=0
>
>

I'm also seeing artifacts in emails by nmh (mail/nmh) in my sent directory 
and in the email cc'd to me.


-- 
Cheers,
Cy Schubert <Cy.Schubert@cschubert.com>
FreeBSD UNIX:  <cy@FreeBSD.org>   Web:  https://FreeBSD.org
NTP:           <cy@nwtime.org>    Web:  https://nwtime.org

			e^(i*pi)+1=0