From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750866AbdCNLDb (ORCPT ); Tue, 14 Mar 2017 07:03:31 -0400 Received: from foss.arm.com ([217.140.101.70]:59560 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744AbdCNLDa (ORCPT ); Tue, 14 Mar 2017 07:03:30 -0400 Subject: Re: kvm/arm64: use-after-free in kvm_vm_ioctl/vmacache_update To: Marc Zyngier , Andrey Konovalov , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Christoffer Dall , Catalin Marinas , Will Deacon , Ingo Molnar , Michal Hocko , Christian Borntraeger , Suraj Jitindar Singh , Markus Elfring , Lorenzo Stoakes , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, LKML References: <3a57c408-8aa5-d339-4176-add4924e817d@arm.com> <0fc0380f-f108-7d20-ee8a-1b044fa1f115@arm.com> Cc: Dmitry Vyukov , Kostya Serebryany , syzkaller From: Suzuki K Poulose Message-ID: <2200dd06-2374-b95d-131b-5a2437d14007@arm.com> Date: Tue, 14 Mar 2017 11:03:22 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: <0fc0380f-f108-7d20-ee8a-1b044fa1f115@arm.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/03/17 09:58, Marc Zyngier wrote: > On 10/03/17 18:37, Suzuki K Poulose wrote: >> On 10/03/17 15:50, Andrey Konovalov wrote: >>> On Fri, Mar 10, 2017 at 2:38 PM, Andrey Konovalov wrote: >>>> Hi, >>>> >>>> I've got the following error report while fuzzing the kernel with syzkaller. >>>> >>>> On linux-next commit 56b8bad5e066c23e8fa273ef5fba50bd3da2ace8 (Mar 8). >>>> >>>> Unfortunately I can't reproduce it. >>>> >>>> ================================================================== >>>> BUG: KASAN: use-after-free in vmacache_update+0x114/0x118 mm/vmacache.c:63 >>>> Read of size 8 at addr ffff80003b9a2040 by task syz-executor/26615 >>>> >>>> CPU: 1 PID: 26615 Comm: syz-executor Not tainted >>>> 4.11.0-rc1-next-20170308-xc2-dirty #3 >>>> Hardware name: Hardkernel ODROID-C2 (DT) >>>> Call trace: >>>> [] dump_backtrace+0x0/0x440 arch/arm64/kernel/traps.c:505 >>>> [] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:228 >>>> [] __dump_stack lib/dump_stack.c:16 [inline] >>>> [] dump_stack+0x110/0x168 lib/dump_stack.c:52 >>>> [] print_address_description+0x60/0x248 mm/kasan/report.c:250 >>>> [] kasan_report_error+0xe8/0x250 mm/kasan/report.c:349 >>>> [] kasan_report mm/kasan/report.c:372 [inline] >>>> [] __asan_report_load8_noabort+0x3c/0x48 mm/kasan/report.c:393 >>>> [] vmacache_update+0x114/0x118 mm/vmacache.c:63 >>>> [] find_vma+0xf8/0x150 mm/mmap.c:2124 >>>> [] kvm_arch_prepare_memory_region+0x2ac/0x488 >>>> arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1817 >>>> [] __kvm_set_memory_region+0x3d8/0x12b8 >>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1026 >>>> [] kvm_set_memory_region+0x38/0x58 >>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1075 >>>> [] kvm_vm_ioctl_set_memory_region >>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1087 [inline] >>>> [] kvm_vm_ioctl+0xb94/0x1308 >>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:2960 >>>> [] vfs_ioctl fs/ioctl.c:45 [inline] >>>> [] do_vfs_ioctl+0x128/0xfc0 fs/ioctl.c:685 >>>> [] SYSC_ioctl fs/ioctl.c:700 [inline] >>>> [] SyS_ioctl+0xa8/0xb8 fs/ioctl.c:691 >>>> [] el0_svc_naked+0x24/0x28 >>>> >>>> Allocated by task 26657: >>>> save_stack_trace_tsk+0x0/0x330 arch/arm64/kernel/stacktrace.c:133 >>>> save_stack_trace+0x20/0x30 arch/arm64/kernel/stacktrace.c:216 >>>> save_stack mm/kasan/kasan.c:515 [inline] >>>> set_track mm/kasan/kasan.c:527 [inline] >>>> kasan_kmalloc+0xd4/0x180 mm/kasan/kasan.c:619 >>>> kasan_slab_alloc+0x14/0x20 mm/kasan/kasan.c:557 >>>> slab_post_alloc_hook mm/slab.h:456 [inline] >>>> slab_alloc_node mm/slub.c:2718 [inline] >>>> slab_alloc mm/slub.c:2726 [inline] >>>> kmem_cache_alloc+0x144/0x230 mm/slub.c:2731 >>>> __split_vma+0x118/0x608 mm/mmap.c:2515 >>>> do_munmap+0x194/0x9b0 mm/mmap.c:2636 >>>> Freed by task 26657: >>>> save_stack_trace_tsk+0x0/0x330 arch/arm64/kernel/stacktrace.c:133 >>>> save_stack_trace+0x20/0x30 arch/arm64/kernel/stacktrace.c:216 >>>> save_stack mm/kasan/kasan.c:515 [inline] >>>> set_track mm/kasan/kasan.c:527 [inline] >>>> kasan_slab_free+0x84/0x198 mm/kasan/kasan.c:592 >>>> slab_free_hook mm/slub.c:1357 [inline] >>>> slab_free_freelist_hook mm/slub.c:1379 [inline] >>>> slab_free mm/slub.c:2961 [inline] >>>> kmem_cache_free+0x80/0x258 mm/slub.c:2983 >>>> __vma_adjust+0x6b0/0xf mm/mmap.c:890] el0_svc_naked+0x24/0x28 >>>> >>>> The buggy address belongs to the object at ffff80003b9a2000 >>>> which belongs to the cache vm_area_struct(647:session-6.scope) of size 184 >>>> The buggy address is located 64 bytes inside of >>>> 184-byte region [ffff80003b9a2000, ffff80003b9a20b8) >>>> The buggy address belongs to the page: >>>> page:ffff7e0000ee6880 count:1 mapcount:0 mapping: (null) index:0x0 >>>> flags: 0xfffc00000000100(slab) >>>> raw: 0fffc00000000100 0000000000000000 0000000000000000 0000000180100010 >>>> raw: 0000000000000000 0000000c00000001 ffff80005a5cc600 ffff80005ac99980 >>>> page dumped because: kasan: bad access detected >>>> page->mem_cgroup:ffff80005ac99980 >>>> >>>> Memory state around the buggy address: >>>> ffff80003b9a1f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff >>>> ffff80003b9a1f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff >>>>> ffff80003b9a2000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>> ^ >>>> ffff80003b9a2080: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fb >>>> ffff80003b9a2100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>> ================================================================== >>> >>> Another one that looks related and doesn't have parts of stack traces missing: >>> >>> ================================================================== >>> BUG: KASAN: use-after-free in find_vma+0x140/0x150 mm/mmap.c:2114 >>> Read of size 8 at addr ffff800031a03e90 by task syz-executor/4360 >>> >>> CPU: 2 PID: 4360 Comm: syz-executor Not tainted >>> 4.11.0-rc1-next-20170308-xc2-dirty #3 >>> Hardware name: Hardkernel ODROID-C2 (DT) >>> Call trace: >>> [] dump_backtrace+0x0/0x440 arch/arm64/kernel/traps.c:505 >>> [] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:228 >>> [] __dump_stack lib/dump_stack.c:16 [inline] >>> [] dump_stack+0x110/0x168 lib/dump_stack.c:52 >>> [] print_address_description+0x60/0x248 mm/kasan/report.c:250 >>> [] kasan_report_error+0xe8/0x250 mm/kasan/report.c:349 >>> [] kasan_report mm/kasan/report.c:372 [inline] >>> [] __asan_report_load8_noabort+0x3c/0x48 mm/kasan/report.c:393 >>> [] find_vma+0x140/0x150 mm/mmap.c:2114 >>> [] kvm_arch_prepare_memory_region+0x2ac/0x488 >>> arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1817 >> >> It looks like we don't take the mmap_sem before calling find_vma() in >> stage2_unmap_memslot() and in kvm_arch_prepare_memory_region(), which is causing >> the race, with probably the test trying to unmap ranges in between. > > That indeed seems like a possible failure mode. The annoying thing is > that we're not exactly in a position to take mmap_sem in > stage2_unmap_memslot, since we hold the kvm->mmu_lock spinlock. We may > have to hold mmap_sem while iterating over all the memslots. > > How about the following (very lightly tested): > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > index 962616fd4ddd..2006a79d5912 100644 > --- a/arch/arm/kvm/mmu.c > +++ b/arch/arm/kvm/mmu.c > @@ -803,6 +803,7 @@ void stage2_unmap_vm(struct kvm *kvm) > int idx; > > idx = srcu_read_lock(&kvm->srcu); > + down_read(¤t->mm->mmap_sem); > spin_lock(&kvm->mmu_lock); > > slots = kvm_memslots(kvm); > @@ -810,6 +811,7 @@ void stage2_unmap_vm(struct kvm *kvm) > stage2_unmap_memslot(kvm, memslot); > > spin_unlock(&kvm->mmu_lock); > + up_read(¤t->mm->mmap_sem); > srcu_read_unlock(&kvm->srcu, idx); > } > > @@ -1813,6 +1815,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > * | memory region | > * +--------------------------------------------+ > */ > + down_read(¤t->mm->mmap_sem); > do { > struct vm_area_struct *vma = find_vma(current->mm, hva); > hva_t vm_start, vm_end; I have added the following hunk : @@ -1844,8 +1847,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, pa += vm_start - vma->vm_start; /* IO region dirty page logging not allowed */ - if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) - return -EINVAL; + if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) { + ret = -EINVAL; + goto out; + } ret = kvm_phys_addr_ioremap(kvm, gpa, pa, vm_end - vm_start, > > I'm much more worried about the other report, as I don't really see yet > how it happens. Coffee required. I have something about that one. Will soon post a patch for it. Suzuki