Messages in this thread Patch in this message | | | Subject | Re: kvm/arm64: use-after-free in kvm_unmap_hva_handler/unmap_stage2_pmds | From | Suzuki K Poulose <> | Date | Tue, 14 Mar 2017 11:07:37 +0000 |
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On 10/03/17 13:34, 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 put_page include/linux/compiler.h:243 [inline] > BUG: KASAN: use-after-free in unmap_stage2_pmds > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:240 [inline] > BUG: KASAN: use-after-free in unmap_stage2_puds > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:269 [inline] > BUG: KASAN: use-after-free in unmap_stage2_range+0x884/0x938 > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:299 > Read of size 8 at addr ffff80004585c000 by task syz-executor/5176
> [<ffff2000080d9664>] put_page include/linux/compiler.h:243 [inline] > [<ffff2000080d9664>] unmap_stage2_pmds > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:240 [inline] > [<ffff2000080d9664>] unmap_stage2_puds > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:269 [inline] > [<ffff2000080d9664>] unmap_stage2_range+0x884/0x938 > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:299 > [<ffff2000080d9740>] kvm_unmap_hva_handler+0x28/0x38 > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1556 > [<ffff2000080d7578>] handle_hva_to_gpa+0x140/0x250 > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1547 > [<ffff2000080db858>] kvm_unmap_hva_range+0x60/0x80 > arch/arm64/kvm/../../../arch/arm/kvm/mmu.c:1579 > [<ffff2000080c12dc>] > kvm_mmu_notifier_invalidate_range_start+0x194/0x278 > arch/arm64/kvm/../../../virt/kvm/kvm_main.c:357 > [<ffff2000083fea58>] __mmu_notifier_invalidate_range_start+0x1d0/0x2a0 > mm/mmu_notifier.c:199 > [<ffff200008395f44>] mmu_notifier_invalidate_range_start > include/linux/mmu_notifier.h:282 [inline] > [<ffff200008395f44>] unmap_vmas+0x12c/0x198 mm/memory.c:1372 > [<ffff2000083a8e00>] unmap_region+0x128/0x230 mm/mmap.c:2460 > [<ffff2000083ae6e0>] update_hiwater_vm include/linux/mm.h:1483 [inline] > [<ffff2000083ae6e0>] remove_vma_list mm/mmap.c:2432 [inline] > [<ffff2000083ae6e0>] do_munmap+0x598/0x9b0 mm/mmap.c:2662 > [<ffff2000083b14a0>] find_vma_links mm/mmap.c:495 [inline] > [<ffff2000083b14a0>] mmap_region+0x138/0xc78 mm/mmap.c:1610 > [<ffff2000083b23ac>] is_file_hugepages include/linux/hugetlb.h:269 [inline] > [<ffff2000083b23ac>] do_mmap+0x3cc/0x848 mm/mmap.c:1446 > [<ffff200008369b0c>] do_mmap_pgoff include/linux/mm.h:2039 [inline] > [<ffff200008369b0c>] vm_mmap_pgoff+0xec/0x120 mm/util.c:305 > [<ffff2000083ac558>] SYSC_mmap_pgoff mm/mmap.c:1475 [inline] > [<ffff2000083ac558>] SyS_mmap_pgoff+0x220/0x420 mm/mmap.c:1458 > [<ffff20000808ecf0>] sys_mmap+0x58/0x80 arch/arm64/kernel/sys.c:37 > [<ffff200008083f70>] el0_svc_naked+0x24/0x28 >
We hold kvm->mmu_lock, while manipulating the stage2 ranges. However, I find that we don't take the lock, when we do it f rom kvm_free_stage2_pgd(), which could potentially have caused a problem with an munmap of a memslot ?
Lightly tested...
commit fa75684dbf0fe845cf8403517d6e0c2c3344a544 Author: Suzuki K Poulose <suzuki.poulose@arm.com> Date: Tue Mar 14 10:26:54 2017 +0000
kvm: arm: Fix locking for kvm_free_stage2_pgd In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling unmap_stage2_range() on the entire memory range for the guest. This could cause problems with other callers (e.g, munmap on a memslot) trying to unmap a range. Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index a07ce3e..7f97063 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) if (kvm->arch.pgd == NULL) return; + spin_lock(&kvm->mmu_lock); unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); + spin_unlock(&kvm->mmu_lock); + /* Free the HW pgd, one page at a time */ free_pages_exact(kvm->arch.pgd, S2_PGD_SIZE); kvm->arch.pgd = NULL;
> The buggy address belongs to the page: > page:ffff7e0001161700 count:0 mapcount:0 mapping: (null) index:0x0 > flags: 0xfffc00000000000() > raw: 0fffc00000000000 0000000000000000 0000000000000000 00000000ffffffff > raw: ffff7e00018c9120 ffff7e0000ea8b60 0000000000000000 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff80004585bf00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff > ffff80004585bf80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff >> ffff80004585c000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff > ^ > ffff80004585c080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff > ffff80004585c100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff > ================================================================== >
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