On Wed, Aug 30, 2017 at 12:30:52PM +0100, Suzuki K Poulose wrote: > commit 6c0d706b563af732adb094c5bf807437e8963e84 upstream. > > In kvm_free_stage2_pgd() we check the stage2 PGD before holding > the lock and proceed to take the lock if it is valid. And we unmap > the page tables, followed by releasing the lock. We reset the PGD > only after dropping this lock, which could cause a race condition > where another thread waiting on or even holding the lock, could > potentially see that the PGD is still valid and proceed to perform > a stage2 operation and later encounter a NULL PGD. > > [223090.242280] Unable to handle kernel NULL pointer dereference at > virtual address 00000040 > [223090.262330] PC is at unmap_stage2_range+0x8c/0x428 > [223090.262332] LR is at kvm_unmap_hva_handler+0x2c/0x3c > [223090.262531] Call trace: > [223090.262533] [<ffff0000080adb78>] unmap_stage2_range+0x8c/0x428 > [223090.262535] [<ffff0000080adf40>] kvm_unmap_hva_handler+0x2c/0x3c > [223090.262537] [<ffff0000080ace2c>] handle_hva_to_gpa+0xb0/0x104 > [223090.262539] [<ffff0000080af988>] kvm_unmap_hva+0x5c/0xbc > [223090.262543] [<ffff0000080a2478>] kvm_mmu_notifier_invalidate_page+0x50/0x8c > [223090.262547] [<ffff0000082274f8>] __mmu_notifier_invalidate_page+0x5c/0x84 > [223090.262551] [<ffff00000820b700>] try_to_unmap_one+0x1d0/0x4a0 > [223090.262553] [<ffff00000820c5c8>] rmap_walk+0x1cc/0x2e0 > [223090.262555] [<ffff00000820c90c>] try_to_unmap+0x74/0xa4 > [223090.262557] [<ffff000008230ce4>] migrate_pages+0x31c/0x5ac > [223090.262561] [<ffff0000081f869c>] compact_zone+0x3fc/0x7ac > [223090.262563] [<ffff0000081f8ae0>] compact_zone_order+0x94/0xb0 > [223090.262564] [<ffff0000081f91c0>] try_to_compact_pages+0x108/0x290 > [223090.262569] [<ffff0000081d5108>] __alloc_pages_direct_compact+0x70/0x1ac > [223090.262571] [<ffff0000081d64a0>] __alloc_pages_nodemask+0x434/0x9f4 > [223090.262572] [<ffff0000082256f0>] alloc_pages_vma+0x230/0x254 > [223090.262574] [<ffff000008235e5c>] do_huge_pmd_anonymous_page+0x114/0x538 > [223090.262576] [<ffff000008201bec>] handle_mm_fault+0xd40/0x17a4 > [223090.262577] [<ffff0000081fb324>] __get_user_pages+0x12c/0x36c > [223090.262578] [<ffff0000081fb804>] get_user_pages_unlocked+0xa4/0x1b8 > [223090.262579] [<ffff0000080a3ce8>] __gfn_to_pfn_memslot+0x280/0x31c > [223090.262580] [<ffff0000080a3dd0>] gfn_to_pfn_prot+0x4c/0x5c > [223090.262582] [<ffff0000080af3f8>] kvm_handle_guest_abort+0x240/0x774 > [223090.262584] [<ffff0000080b2bac>] handle_exit+0x11c/0x1ac > [223090.262586] [<ffff0000080ab99c>] kvm_arch_vcpu_ioctl_run+0x31c/0x648 > [223090.262587] [<ffff0000080a1d78>] kvm_vcpu_ioctl+0x378/0x768 > [223090.262590] [<ffff00000825df5c>] do_vfs_ioctl+0x324/0x5a4 > [223090.262591] [<ffff00000825e26c>] SyS_ioctl+0x90/0xa4 > [223090.262595] [<ffff000008085d84>] el0_svc_naked+0x38/0x3c > > This patch moves the stage2 PGD manipulation under the lock. > > Reported-by: Alexander Graf <agraf@xxxxxxx> > Cc: Mark Rutland <mark.rutland@xxxxxxx> > Cc: Marc Zyngier <marc.zyngier@xxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # 4.10.x and earlier > Reviewed-by: Christoffer Dall <cdall@xxxxxxxxxx> > Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx> > > --- > > Hi, > > Looks like we missed sending this to stable. Please apply for 4.10.x and > earlier. 4.11.y and later versions have it already. Only applied to 4.9-stable, can you please provide a backport for 4.4 and 3.18 if you want it there? thanks, greg k-h