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While working on XSA-361 and its follow-ups, I failed to spot another place where the kernel mapping part of an operation was not treated the same as the user space part. Detect and propagate errors and add a 2nd pr_debug(). Signed-off-by: Jan Beulich Reviewed-by: Juergen Gross Link: https://lore.kernel.org/r/c2513395-74dc-aea3-9192-fd265aa44e35@suse.com Signed-off-by: Juergen Gross Signed-off-by: Demi Marie Obenour Co-authored-by: Demi Marie Obenour --- drivers/xen/gntdev.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 54fee4087bf1078803c230ad2081aafa8415cf53..8cf9f2074c5d57bff81364d7d6a70b0007a85e44 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -407,6 +407,14 @@ static void __unmap_grant_pages_done(int result, map->unmap_ops[offset+i].handle, map->unmap_ops[offset+i].status); map->unmap_ops[offset+i].handle = -1; + if (use_ptemod) { + WARN_ON(map->kunmap_ops[offset+i].status && + map->kunmap_ops[offset+i].handle != -1); + pr_debug("kunmap handle=%u st=%d\n", + map->kunmap_ops[offset+i].handle, + map->kunmap_ops[offset+i].status); + map->kunmap_ops[offset+i].handle = -1; + } } /* * Decrease the live-grant counter. 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Vefa Bicakci" , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Demi Marie Obenour Subject: [PATCH 2/3] xen/gntdev: Prevent leaking grants Date: Sun, 30 Oct 2022 03:12:42 -0400 Message-Id: <20221030071243.1580-3-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221030071243.1580-1-demi@invisiblethingslab.com> References: <20221030071243.1580-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_PASS,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748096992864138561?= X-GMAIL-MSGID: =?utf-8?q?1748096992864138561?= From: "M. Vefa Bicakci" commit 0991028cd49567d7016d1b224fe0117c35059f86 upstream. Prior to this commit, if a grant mapping operation failed partially, some of the entries in the map_ops array would be invalid, whereas all of the entries in the kmap_ops array would be valid. This in turn would cause the following logic in gntdev_map_grant_pages to become invalid: for (i = 0; i < map->count; i++) { if (map->map_ops[i].status == GNTST_okay) { map->unmap_ops[i].handle = map->map_ops[i].handle; if (!use_ptemod) alloced++; } if (use_ptemod) { if (map->kmap_ops[i].status == GNTST_okay) { if (map->map_ops[i].status == GNTST_okay) alloced++; map->kunmap_ops[i].handle = map->kmap_ops[i].handle; } } } ... atomic_add(alloced, &map->live_grants); Assume that use_ptemod is true (i.e., the domain mapping the granted pages is a paravirtualized domain). In the code excerpt above, note that the "alloced" variable is only incremented when both kmap_ops[i].status and map_ops[i].status are set to GNTST_okay (i.e., both mapping operations are successful). However, as also noted above, there are cases where a grant mapping operation fails partially, breaking the assumption of the code excerpt above. The aforementioned causes map->live_grants to be incorrectly set. In some cases, all of the map_ops mappings fail, but all of the kmap_ops mappings succeed, meaning that live_grants may remain zero. This in turn makes it impossible to unmap the successfully grant-mapped pages pointed to by kmap_ops, because unmap_grant_pages has the following snippet of code at its beginning: if (atomic_read(&map->live_grants) == 0) return; /* Nothing to do */ In other cases where only some of the map_ops mappings fail but all kmap_ops mappings succeed, live_grants is made positive, but when the user requests unmapping the grant-mapped pages, __unmap_grant_pages_done will then make map->live_grants negative, because the latter function does not check if all of the pages that were requested to be unmapped were actually unmapped, and the same function unconditionally subtracts "data->count" (i.e., a value that can be greater than map->live_grants) from map->live_grants. The side effects of a negative live_grants value have not been studied. The net effect of all of this is that grant references are leaked in one of the above conditions. In Qubes OS v4.1 (which uses Xen's grant mechanism extensively for X11 GUI isolation), this issue manifests itself with warning messages like the following to be printed out by the Linux kernel in the VM that had granted pages (that contain X11 GUI window data) to dom0: "g.e. 0x1234 still pending", especially after the user rapidly resizes GUI VM windows (causing some grant-mapping operations to partially or completely fail, due to the fact that the VM unshares some of the pages as part of the window resizing, making the pages impossible to grant-map from dom0). The fix for this issue involves counting all successful map_ops and kmap_ops mappings separately, and then adding the sum to live_grants. During unmapping, only the number of successfully unmapped grants is subtracted from live_grants. The code is also modified to check for negative live_grants values after the subtraction and warn the user. Link: https://github.com/QubesOS/qubes-issues/issues/7631 Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()") Cc: stable@vger.kernel.org Signed-off-by: M. Vefa Bicakci Acked-by: Demi Marie Obenour Reviewed-by: Juergen Gross Link: https://lore.kernel.org/r/20221002222006.2077-2-m.v.b@runbox.com Signed-off-by: Juergen Gross Signed-off-by: Demi Marie Obenour --- drivers/xen/gntdev.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 8cf9f2074c5d57bff81364d7d6a70b0007a85e44..62a65122c73fbfe673405ce90a53c5f364b75082 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -372,8 +372,7 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map) for (i = 0; i < map->count; i++) { if (map->map_ops[i].status == GNTST_okay) { map->unmap_ops[i].handle = map->map_ops[i].handle; - if (!use_ptemod) - alloced++; + alloced++; } else if (!err) err = -EINVAL; @@ -382,8 +381,7 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map) if (use_ptemod) { if (map->kmap_ops[i].status == GNTST_okay) { - if (map->map_ops[i].status == GNTST_okay) - alloced++; + alloced++; map->kunmap_ops[i].handle = map->kmap_ops[i].handle; } else if (!err) err = -EINVAL; @@ -399,8 +397,14 @@ static void __unmap_grant_pages_done(int result, unsigned int i; struct gntdev_grant_map *map = data->data; unsigned int offset = data->unmap_ops - map->unmap_ops; + int successful_unmaps = 0; + int live_grants; for (i = 0; i < data->count; i++) { + if (map->unmap_ops[offset + i].status == GNTST_okay && + map->unmap_ops[offset + i].handle != -1) + successful_unmaps++; + WARN_ON(map->unmap_ops[offset+i].status && map->unmap_ops[offset+i].handle != -1); pr_debug("unmap handle=%d st=%d\n", @@ -408,6 +412,10 @@ static void __unmap_grant_pages_done(int result, map->unmap_ops[offset+i].status); map->unmap_ops[offset+i].handle = -1; if (use_ptemod) { + if (map->kunmap_ops[offset + i].status == GNTST_okay && + map->kunmap_ops[offset + i].handle != -1) + successful_unmaps++; + WARN_ON(map->kunmap_ops[offset+i].status && map->kunmap_ops[offset+i].handle != -1); pr_debug("kunmap handle=%u st=%d\n", @@ -416,11 +424,15 @@ static void __unmap_grant_pages_done(int result, map->kunmap_ops[offset+i].handle = -1; } } + /* * Decrease the live-grant counter. This must happen after the loop to * prevent premature reuse of the grants by gnttab_mmap(). */ - atomic_sub(data->count, &map->live_grants); + live_grants = atomic_sub_return(successful_unmaps, &map->live_grants); + if (WARN_ON(live_grants < 0)) + pr_err("%s: live_grants became negative (%d) after unmapping %d pages!\n", + __func__, live_grants, successful_unmaps); /* Release reference taken by __unmap_grant_pages */ gntdev_put_map(NULL, map); From patchwork Sun Oct 30 07:12:43 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 12935 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a5d:6687:0:0:0:0:0 with SMTP id l7csp1681947wru; Sun, 30 Oct 2022 00:33:26 -0700 (PDT) X-Google-Smtp-Source: AMsMyM5MEXFoXeICSx9gtUNdqaIBKK+6uGwuqbIoe0MzG8cr50IBLmF6J6CbWC/gqTe6JX+lxt2i X-Received: by 2002:a17:902:ebc4:b0:186:b32c:4ce5 with SMTP id p4-20020a170902ebc400b00186b32c4ce5mr8058703plg.74.1667115206150; Sun, 30 Oct 2022 00:33:26 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1667115206; cv=none; d=google.com; s=arc-20160816; b=B0K5wbIWufOdq7H/Ju/vCW/AP0tQ3pwSml9Nv6ZkSBCWJV2gcXpxOGz4Mf0ASAD90e zxiMNTiDqvyJOhkD8tiYc7/dNw351TWoJCHlNLqaj7rFyJ3zUylA+KMds2Iy21IzSGXo hoC726/Mrp2NczqoQXzbs+Wjb2gOsrbspzVeu3W9XSLzL3Daba21HiRw9IDZnmoLvV66 Pjv+IEFBSOhogCqDL92y8RCJAucuTLSB6X+UAU2sTCdGOptFbmUgiANL61W0GHV8gho3 4FKLk5V2+73G3//DWyFeAd6YxFJimoU9nl2uXmbtqBA6pJlgJN0jPY2coA0pAEwzF412 2Uvg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=Mo8RRVU/BCqu317V/TpNAiSZ8pju9kQTzGf3AAdnqs4=; b=rtXpcdQ/LCSkigaBOQt6dz/OZv9c775ivNHD4ifkfx9k/M1JfVM448eR1l0VYUCR+p z17pg6ujwVrkFarOxwYUxd2qWk0KgqULqHnmrV9KLhOEvKb0ZHriLwkA4WcDQwaglhV5 sEToPnnOYRXgd5zXsBr7G8urFYzeOQnTqIbweAmVNl0Z1uGT3c10xr19Wip9BOo5LHzq mwSCamRoFdlVyJnS/ylKPIii03wwy5HKyeVh9wLVM+qyLa/2EBj/SRCXrvSFEM+DKlzY RyGXUs20ScGlf1L8ItC/l9WJ6YeXK/WFwwwh1deMuipx/UUNF0LCfHQqevvwAQCgUmtl ieww== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b=dfcMRjyr; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=NvntkGDB; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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Vefa Bicakci" , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH 3/3] xen/gntdev: Accommodate VMA splitting Date: Sun, 30 Oct 2022 03:12:43 -0400 Message-Id: <20221030071243.1580-4-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221030071243.1580-1-demi@invisiblethingslab.com> References: <20221030071243.1580-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_PASS,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748096993997316947?= X-GMAIL-MSGID: =?utf-8?q?1748096993997316947?= From: "M. Vefa Bicakci" Prior to this commit, the gntdev driver code did not handle the following scenario correctly with paravirtualized (PV) Xen domains: * User process sets up a gntdev mapping composed of two grant mappings (i.e., two pages shared by another Xen domain). * User process munmap()s one of the pages. * User process munmap()s the remaining page. * User process exits. In the scenario above, the user process would cause the kernel to log the following messages in dmesg for the first munmap(), and the second munmap() call would result in similar log messages: BUG: Bad page map in process doublemap.test pte:... pmd:... page:0000000057c97bff refcount:1 mapcount:-1 \ mapping:0000000000000000 index:0x0 pfn:... ... page dumped because: bad pte ... file:gntdev fault:0x0 mmap:gntdev_mmap [xen_gntdev] readpage:0x0 ... Call Trace: dump_stack_lvl+0x46/0x5e print_bad_pte.cold+0x66/0xb6 unmap_page_range+0x7e5/0xdc0 unmap_vmas+0x78/0xf0 unmap_region+0xa8/0x110 __do_munmap+0x1ea/0x4e0 __vm_munmap+0x75/0x120 __x64_sys_munmap+0x28/0x40 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x61/0xcb ... For each munmap() call, the Xen hypervisor (if built with CONFIG_DEBUG) would print out the following and trigger a general protection fault in the affected Xen PV domain: (XEN) d0v... Attempt to implicitly unmap d0's grant PTE ... (XEN) d0v... Attempt to implicitly unmap d0's grant PTE ... As of this writing, gntdev_grant_map structure's vma field (referred to as map->vma below) is mainly used for checking the start and end addresses of mappings. However, with split VMAs, these may change, and there could be more than one VMA associated with a gntdev mapping. Hence, remove the use of map->vma and rely on map->pages_vm_start for the original start address and on (map->count << PAGE_SHIFT) for the original mapping size. Let the invalidate() and find_special_page() hooks use these. Also, given that there can be multiple VMAs associated with a gntdev mapping, move the "mmu_interval_notifier_remove(&map->notifier)" call to the end of gntdev_put_map, so that the MMU notifier is only removed after the closing of the last remaining VMA. Finally, use an atomic to prevent inadvertent gntdev mapping re-use, instead of using the map->live_grants atomic counter and/or the map->vma pointer (the latter of which is now removed). This prevents the userspace from mmap()'ing (with MAP_FIXED) a gntdev mapping over the same address range as a previously set up gntdev mapping. This scenario can be summarized with the following call-trace, which was valid prior to this commit: mmap gntdev_mmap mmap (repeat mmap with MAP_FIXED over the same address range) gntdev_invalidate unmap_grant_pages (sets 'being_removed' entries to true) gnttab_unmap_refs_async unmap_single_vma gntdev_mmap (maps the shared pages again) munmap gntdev_invalidate unmap_grant_pages (no-op because 'being_removed' entries are true) unmap_single_vma (For PV domains, Xen reports that a granted page is being unmapped and triggers a general protection fault in the affected domain, if Xen was built with CONFIG_DEBUG) The fix for this last scenario could be worth its own commit, but we opted for a single commit, because removing the gntdev_grant_map structure's vma field requires guarding the entry to gntdev_mmap(), and the live_grants atomic counter is not sufficient on its own to prevent the mmap() over a pre-existing mapping. Link: https://github.com/QubesOS/qubes-issues/issues/7631 Fixes: ab31523c2fca ("xen/gntdev: allow usermode to map granted pages") Cc: stable@vger.kernel.org Signed-off-by: M. Vefa Bicakci Reviewed-by: Juergen Gross Link: https://lore.kernel.org/r/20221002222006.2077-3-m.v.b@runbox.com Signed-off-by: Juergen Gross --- drivers/xen/gntdev-common.h | 3 +- drivers/xen/gntdev.c | 58 ++++++++++++++++--------------------- 2 files changed, 27 insertions(+), 34 deletions(-) diff --git a/drivers/xen/gntdev-common.h b/drivers/xen/gntdev-common.h index 40ef379c28ab01a3a11008cb0f85a1b3fde134ca..9c286b2a19001616ae0e9986be13905891b5f5ff 100644 --- a/drivers/xen/gntdev-common.h +++ b/drivers/xen/gntdev-common.h @@ -44,9 +44,10 @@ struct gntdev_unmap_notify { }; struct gntdev_grant_map { + atomic_t in_use; struct mmu_interval_notifier notifier; + bool notifier_init; struct list_head next; - struct vm_area_struct *vma; int index; int count; int flags; diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 62a65122c73fbfe673405ce90a53c5f364b75082..862de00cfe89209cf28f7e7e87cf325e40f1fc4b 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -276,6 +276,9 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map) */ } + if (use_ptemod && map->notifier_init) + mmu_interval_notifier_remove(&map->notifier); + if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { notify_remote_via_evtchn(map->notify.event); evtchn_put(map->notify.event); @@ -288,7 +291,7 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map) static int find_grant_ptes(pte_t *pte, unsigned long addr, void *data) { struct gntdev_grant_map *map = data; - unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT; + unsigned int pgnr = (addr - map->pages_vm_start) >> PAGE_SHIFT; int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte; u64 pte_maddr; @@ -513,11 +516,7 @@ static void gntdev_vma_close(struct vm_area_struct *vma) struct gntdev_priv *priv = file->private_data; pr_debug("gntdev_vma_close %p\n", vma); - if (use_ptemod) { - WARN_ON(map->vma != vma); - mmu_interval_notifier_remove(&map->notifier); - map->vma = NULL; - } + vma->vm_private_data = NULL; gntdev_put_map(priv, map); } @@ -545,29 +544,30 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn, struct gntdev_grant_map *map = container_of(mn, struct gntdev_grant_map, notifier); unsigned long mstart, mend; + unsigned long map_start, map_end; if (!mmu_notifier_range_blockable(range)) return false; + map_start = map->pages_vm_start; + map_end = map->pages_vm_start + (map->count << PAGE_SHIFT); + /* * If the VMA is split or otherwise changed the notifier is not * updated, but we don't want to process VA's outside the modified * VMA. FIXME: It would be much more understandable to just prevent * modifying the VMA in the first place. */ - if (map->vma->vm_start >= range->end || - map->vma->vm_end <= range->start) + if (map_start >= range->end || map_end <= range->start) return true; - mstart = max(range->start, map->vma->vm_start); - mend = min(range->end, map->vma->vm_end); + mstart = max(range->start, map_start); + mend = min(range->end, map_end); pr_debug("map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n", - map->index, map->count, - map->vma->vm_start, map->vma->vm_end, - range->start, range->end, mstart, mend); - unmap_grant_pages(map, - (mstart - map->vma->vm_start) >> PAGE_SHIFT, - (mend - mstart) >> PAGE_SHIFT); + map->index, map->count, map_start, map_end, + range->start, range->end, mstart, mend); + unmap_grant_pages(map, (mstart - map_start) >> PAGE_SHIFT, + (mend - mstart) >> PAGE_SHIFT); return true; } @@ -1047,18 +1047,15 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) return -EINVAL; pr_debug("map %d+%d at %lx (pgoff %lx)\n", - index, count, vma->vm_start, vma->vm_pgoff); + index, count, vma->vm_start, vma->vm_pgoff); mutex_lock(&priv->lock); map = gntdev_find_map_index(priv, index, count); if (!map) goto unlock_out; - if (use_ptemod && map->vma) + if (!atomic_add_unless(&map->in_use, 1, 1)) goto unlock_out; - if (atomic_read(&map->live_grants)) { - err = -EAGAIN; - goto unlock_out; - } + refcount_inc(&map->users); vma->vm_ops = &gntdev_vmops; @@ -1079,15 +1076,16 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) map->flags |= GNTMAP_readonly; } + map->pages_vm_start = vma->vm_start; + if (use_ptemod) { - map->vma = vma; err = mmu_interval_notifier_insert_locked( &map->notifier, vma->vm_mm, vma->vm_start, vma->vm_end - vma->vm_start, &gntdev_mmu_ops); - if (err) { - map->vma = NULL; + if (err) goto out_unlock_put; - } + + map->notifier_init = true; } mutex_unlock(&priv->lock); @@ -1104,7 +1102,6 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) */ mmu_interval_read_begin(&map->notifier); - map->pages_vm_start = vma->vm_start; err = apply_to_page_range(vma->vm_mm, vma->vm_start, vma->vm_end - vma->vm_start, find_grant_ptes, map); @@ -1150,13 +1147,8 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) out_unlock_put: mutex_unlock(&priv->lock); out_put_map: - if (use_ptemod) { + if (use_ptemod) unmap_grant_pages(map, 0, map->count); - if (map->vma) { - mmu_interval_notifier_remove(&map->notifier); - map->vma = NULL; - } - } gntdev_put_map(priv, map); return err; }