On 14/03/2017 12:07, Suzuki K Poulose wrote: > 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@xxxxxxx> > 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@xxxxxxx> > Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > > 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; Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > > >> 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 >> ================================================================== >> >
