Date: Thu, 20 Jul 2023 09:32:31 -0700 From: Cy Schubert <Cy.Schubert@cschubert.com> To: Konstantin Belousov <kib@FreeBSD.org> Cc: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: Re: git: 21e45c30c35c - main - mmap(MAP_STACK): on stack grow, use original protection Message-ID: <20230720163231.B1D4277@slippy.cwsent.com> In-Reply-To: <202307201412.36KECDSU084918@gitrepo.freebsd.org> References: <202307201412.36KECDSU084918@gitrepo.freebsd.org>
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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=21e45c30c35c9aa732073f725924caf5 > 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 addrbos > , 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_map > _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
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