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

In reply to: Konstantin Belousov : "Re: git: 21e45c30c35c - main - mmap(MAP_STACK): on stack grow, use original protection"
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From: Gary Jennejohn <garyj_at_gmx.de>
Date: Thu, 20 Jul 2023 18:38:03 UTC
On Thu, 20 Jul 2023 20:34:35 +0300
Konstantin Belousov <kostikbel@gmail.com> wrote:

> On Thu, Jul 20, 2023 at 10:06:24AM -0700, Cy Schubert wrote:
> > In message <20230720164145.0CF1311F@slippy.cwsent.com>, Cy Schubert writes:
> > > 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=21e45c30c35c9aa732073f725924
> > > ca
> > > > 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 grow
> > > n
> > > > >     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 t
> > > he
> > > > >     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_ssi
> > > ze
> > > > ,
> > > > >      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 add
> > > rb
> > > > 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 operation
> > > s.
> > > > > + *
> > > > > + *	For stack gap map entries (MAP_ENTRY_GUARD | MAP_ENTRY_GROWS_DO
> > > WN
> > > > > + *	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
> > >
> > >
> >
> > Sometimes this occurs at screen start. Then it hangs.
> >
> > slippy$ screen
> > pid 7275 comm screen-4.9.0 has trashed its stack, killing
>
> Can you check this?
>
> diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
> index 8c864c943f5d..4c5f1c08954d 100644
> --- a/sys/vm/vm_map.c
> +++ b/sys/vm/vm_map.c
> @@ -4202,7 +4202,8 @@ vm_map_copy_entry(
>  			    src_entry->start);
>  		} else {
>  			dst_entry->object.vm_object = NULL;
> -			dst_entry->offset = 0;
> +			if ((dst_entry->eflags & MAP_ENTRY_GUARD) == 0)
> +				dst_entry->offset = 0;
>  			if (src_entry->cred != NULL) {
>  				dst_entry->cred = curthread->td_ucred;
>  				crhold(dst_entry->cred);
>
>

Works for me.  I tested with both pkg and screen and saw no errors.

--
Gary Jennejohn