Date: Tue, 30 Jun 2026 17:19:06 +0000 From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 97a064125e8a - main - device_pager: Avoid double-insertion of pages into the pager list Message-ID: <6a43fa8a.445a2.7d97a357@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=97a064125e8a0326159dcc35e9c522c049eb3b95 commit 97a064125e8a0326159dcc35e9c522c049eb3b95 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2026-06-22 14:40:22 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2026-06-30 17:00:22 +0000 device_pager: Avoid double-insertion of pages into the pager list Unmanaged device pager objects maintain a linked list of pages that were returned from the fault handler. Initially, such pages are valid, but msync(MS_INVALIDATE) can mark them invalid (and clean). They are not removed from page tables (since they are unmanaged), but a subsequent mlock() call can trigger a page fault that is handled by the pager. dev_pager_getpages() then re-inserts the page into the linked list even though it's already present there. This patch fixes the problem by removing the linked list. OBJ_PG_DTOR is set, so vm_object_terminate_pages() does nothing, and dev_pager_dealloc() instead handles cleanup of the object. Add a regression test case which triggers a queue.h assertion failure in unpatched kernels. Note, in stable branches we should avoid changing the layout of struct vm_object. Approved by: so Security: FreeBSD-SA-26:37.vm Security: CVE-2026-49418 Reported by: slidybat Reviewed by: kib Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D57743 --- sys/vm/device_pager.c | 36 ++++++++++++++++++++---------------- sys/vm/vm_object.h | 1 - sys/vm/vm_page.c | 6 ++++-- tests/sys/vm/mmap_test.c | 30 ++++++++++++++++++++++++++++++ 4 files changed, 54 insertions(+), 19 deletions(-) diff --git a/sys/vm/device_pager.c b/sys/vm/device_pager.c index 221969307ba4..9277d6255418 100644 --- a/sys/vm/device_pager.c +++ b/sys/vm/device_pager.c @@ -213,7 +213,8 @@ again: object1 = NULL; object->handle = handle; object->un_pager.devp.ops = ops; - TAILQ_INIT(&object->un_pager.devp.devp_pglist); + if (object->type == OBJT_DEVICE) + vm_object_set_flag(object, OBJ_PG_DTOR); TAILQ_INSERT_TAIL(&dev_pager_object_list, object, pager_object_list); mtx_unlock(&dev_pager_mtx); @@ -325,15 +326,12 @@ dev_pager_free_page(vm_object_t object, vm_page_t m) KASSERT((object->type == OBJT_DEVICE && (m->oflags & VPO_UNMANAGED) != 0), ("Managed device or page obj %p m %p", object, m)); - TAILQ_REMOVE(&object->un_pager.devp.devp_pglist, m, plinks.q); vm_page_putfake(m); } static void dev_pager_dealloc(vm_object_t object) { - vm_page_t m; - VM_OBJECT_WUNLOCK(object); object->un_pager.devp.ops->cdev_pg_dtor(object->un_pager.devp.handle); @@ -343,15 +341,25 @@ dev_pager_dealloc(vm_object_t object) VM_OBJECT_WLOCK(object); if (object->type == OBJT_DEVICE) { - /* - * Free up our fake pages. - */ - while ((m = TAILQ_FIRST(&object->un_pager.devp.devp_pglist)) - != NULL) { - if (vm_page_busy_acquire(m, VM_ALLOC_WAITFAIL) == 0) - continue; + struct pctrie_iter pages; + vm_page_t m; - dev_pager_free_page(object, m); + vm_page_iter_init(&pages, object); +restart: + VM_RADIX_FOREACH(m, &pages) { + if (!vm_page_busy_acquire(m, VM_ALLOC_WAITFAIL)) { + pctrie_iter_reset(&pages); + goto restart; + } + if (vm_page_iter_remove(&pages, m)) { + /* + * We could end up with invalid pages installed + * by the generic page fault handler. Typically + * these are replaced by the device pager. + */ + vm_page_free(m); + } else if ((m->flags & PG_FICTITIOUS) != 0) + dev_pager_free_page(object, m); } } object->handle = NULL; @@ -380,10 +388,6 @@ dev_pager_getpages(vm_object_t object, vm_page_t *ma, int count, int *rbehind, (object->type == OBJT_MGTDEVICE && (ma[0]->oflags & VPO_UNMANAGED) == 0), ("Wrong page type %p %p", ma[0], object)); - if (object->type == OBJT_DEVICE) { - TAILQ_INSERT_TAIL(&object->un_pager.devp.devp_pglist, - ma[0], plinks.q); - } if (rbehind) *rbehind = 0; if (rahead) diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h index e01d8ad79995..5a3a78b5b5a1 100644 --- a/sys/vm/vm_object.h +++ b/sys/vm/vm_object.h @@ -134,7 +134,6 @@ struct vm_object { * devp_pglist - list of allocated pages */ struct { - TAILQ_HEAD(, vm_page) devp_pglist; const struct cdev_pager_ops *ops; void *handle; } devp; diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c index 8c953149e6de..8697d9361d84 100644 --- a/sys/vm/vm_page.c +++ b/sys/vm/vm_page.c @@ -1378,8 +1378,10 @@ vm_page_putfake(vm_page_t m) KASSERT((m->oflags & VPO_UNMANAGED) != 0, ("managed %p", m)); KASSERT((m->flags & PG_FICTITIOUS) != 0, ("vm_page_putfake: bad page %p", m)); - vm_page_assert_xbusied(m); - vm_page_busy_free(m); + if (m->object != NULL) { + vm_page_assert_xbusied(m); + vm_page_busy_free(m); + } uma_zfree(fakepg_zone, m); } diff --git a/tests/sys/vm/mmap_test.c b/tests/sys/vm/mmap_test.c index 27d02ae667fb..78164fa27680 100644 --- a/tests/sys/vm/mmap_test.c +++ b/tests/sys/vm/mmap_test.c @@ -363,6 +363,35 @@ ATF_TC_BODY(mmap__maxprot_shm, tc) ATF_REQUIRE(close(fd) == 0); } +/* A regression test for a bug in the device pager. */ +ATF_TC_WITHOUT_HEAD(mmap__device_reinsert); +ATF_TC_BODY(mmap__device_reinsert, tc) +{ + void *p; + int fd; + + fd = open("/dev/devstat", O_RDONLY); + ATF_REQUIRE(fd >= 0); + + p = mmap(NULL, getpagesize(), PROT_READ, MAP_SHARED, fd, 0); + ATF_REQUIRE(p != MAP_FAILED); + + /* + * Use mlock() to trigger a fault, since msync() will not actually + * remove the page from the process page tables. + */ + ATF_REQUIRE(mlock(p, getpagesize()) == 0); + ATF_REQUIRE(munlock(p, getpagesize()) == 0); + ATF_REQUIRE(msync(p, getpagesize(), MS_INVALIDATE) == 0); + ATF_REQUIRE(mlock(p, getpagesize()) == 0); + ATF_REQUIRE(munlock(p, getpagesize()) == 0); + ATF_REQUIRE(msync(p, getpagesize(), MS_INVALIDATE) == 0); + ATF_REQUIRE(mlock(p, getpagesize()) == 0); + ATF_REQUIRE(munlock(p, getpagesize()) == 0); + + ATF_REQUIRE(munmap(p, getpagesize()) == 0); +} + ATF_TP_ADD_TCS(tp) { ATF_TP_ADD_TC(tp, mmap__map_at_zero); @@ -372,6 +401,7 @@ ATF_TP_ADD_TCS(tp) ATF_TP_ADD_TC(tp, mmap__write_only); ATF_TP_ADD_TC(tp, mmap__maxprot_basic); ATF_TP_ADD_TC(tp, mmap__maxprot_shm); + ATF_TP_ADD_TC(tp, mmap__device_reinsert); return (atf_no_error()); }home | help
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