Re: kvm/arm64: use-after-free in kvm_vm_ioctl/vmacache_update

From: Andrey Konovalov
Date: Tue Apr 11 2017 - 11:41:44 EST

On Tue, Apr 11, 2017 at 5:36 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> On 11/04/17 16:26, Andrey Konovalov wrote:
>> On Tue, Mar 14, 2017 at 1:26 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>>> On 14/03/17 11:03, Suzuki K Poulose wrote:
>>>> 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 <andreyknvl@xxxxxxxxxx> 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:
>>>>>>>> [<ffff20000808fbb0>] dump_backtrace+0x0/0x440 arch/arm64/kernel/traps.c:505
>>>>>>>> [<ffff200008090010>] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:228
>>>>>>>> [<ffff2000088e9578>] __dump_stack lib/dump_stack.c:16 [inline]
>>>>>>>> [<ffff2000088e9578>] dump_stack+0x110/0x168 lib/dump_stack.c:52
>>>>>>>> [<ffff200008414018>] print_address_description+0x60/0x248 mm/kasan/report.c:250
>>>>>>>> [<ffff2000084142e8>] kasan_report_error+0xe8/0x250 mm/kasan/report.c:349
>>>>>>>> [<ffff200008414564>] kasan_report mm/kasan/report.c:372 [inline]
>>>>>>>> [<ffff200008414564>] __asan_report_load8_noabort+0x3c/0x48 mm/kasan/report.c:393
>>>>>>>> [<ffff200008383f64>] vmacache_update+0x114/0x118 mm/vmacache.c:63
>>>>>>>> [<ffff2000083a9000>] find_vma+0xf8/0x150 mm/mmap.c:2124
>>>>>>>> [<ffff2000080dc19c>] kvm_arch_prepare_memory_region+0x2ac/0x488
>>>>>>>> arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1817
>>>>>>>> [<ffff2000080c2920>] __kvm_set_memory_region+0x3d8/0x12b8
>>>>>>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1026
>>>>>>>> [<ffff2000080c3838>] kvm_set_memory_region+0x38/0x58
>>>>>>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1075
>>>>>>>> [<ffff2000080c747c>] kvm_vm_ioctl_set_memory_region
>>>>>>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:1087 [inline]
>>>>>>>> [<ffff2000080c747c>] kvm_vm_ioctl+0xb94/0x1308
>>>>>>>> arch/arm64/kvm/../../../virt/kvm/kvm_main.c:2960
>>>>>>>> [<ffff20000848f928>] vfs_ioctl fs/ioctl.c:45 [inline]
>>>>>>>> [<ffff20000848f928>] do_vfs_ioctl+0x128/0xfc0 fs/ioctl.c:685
>>>>>>>> [<ffff200008490868>] SYSC_ioctl fs/ioctl.c:700 [inline]
>>>>>>>> [<ffff200008490868>] SyS_ioctl+0xa8/0xb8 fs/ioctl.c:691
>>>>>>>> [<ffff200008083f70>] 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:
>>>>>>> [<ffff20000808fbb0>] dump_backtrace+0x0/0x440 arch/arm64/kernel/traps.c:505
>>>>>>> [<ffff200008090010>] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:228
>>>>>>> [<ffff2000088e9578>] __dump_stack lib/dump_stack.c:16 [inline]
>>>>>>> [<ffff2000088e9578>] dump_stack+0x110/0x168 lib/dump_stack.c:52
>>>>>>> [<ffff200008414018>] print_address_description+0x60/0x248 mm/kasan/report.c:250
>>>>>>> [<ffff2000084142e8>] kasan_report_error+0xe8/0x250 mm/kasan/report.c:349
>>>>>>> [<ffff200008414564>] kasan_report mm/kasan/report.c:372 [inline]
>>>>>>> [<ffff200008414564>] __asan_report_load8_noabort+0x3c/0x48 mm/kasan/report.c:393
>>>>>>> [<ffff2000083a9048>] find_vma+0x140/0x150 mm/mmap.c:2114
>>>>>>> [<ffff2000080dc19c>] 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(&current->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(&current->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(&current->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,
>>>>
>>>
>>> Ah, of course... Thanks for pointing that out, I'll fix it as I post a
>>> proper patch.
>>>
>>> Thanks,
>>>
>>> M.
>>> --
>>> Jazz is not dead. It just smells funny...
>>
>> Hi,
>>
>> I've got this report again on linux-next 4c3c5cd02318 (Apr 5).
>>
>> It seems that it's still not fixed.
>>
>> Thanks!
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in vmacache_update+0x114/0x118 mm/vmacache.c:63
>> Read of size 8 at addr ffff80004d53aae8 by task syz-executor/23095
>>
>> CPU: 0 PID: 23095 Comm: syz-executor Not tainted
>> 4.11.0-rc5-next-20170405-xc2-09030-g4c3c5cd02318-dirty #4
>
> The fixes went into -rc6. Can you please give it a go?

Ah, OK, I assumed they were in the linux-next revision I used.

Thanks!

>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...
>
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