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SUSE: CVE-2021-47094: SUSE Linux Security Advisory

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SUSE: CVE-2021-47094: SUSE Linux Security Advisory

Severity
4
CVSS
(AV:L/AC:M/Au:N/C:P/I:P/A:P)
Published
03/04/2024
Created
08/16/2024
Added
08/09/2024
Modified
08/09/2024

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Don't advance iterator after restart due to yielding After dropping mmu_lock in the TDP MMU, restart the iterator during tdp_iter_next() and do not advance the iterator. Advancing the iterator results in skipping the top-level SPTE and all its children, which is fatal if any of the skipped SPTEs were not visited before yielding. When zapping all SPTEs, i.e. when min_level == root_level, restarting the iter and then invoking tdp_iter_next() is always fatal if the current gfn has as a valid SPTE, as advancing the iterator results in try_step_side() skipping the current gfn, which wasn't visited before yielding. Sprinkle WARNs on iter->yielded being true in various helpers that are often used in conjunction with yielding, and tag the helper with __must_check to reduce the probabily of improper usage. Failing to zap a top-level SPTE manifests in one of two ways. If a valid SPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(), the shadow page will be leaked and KVM will WARN accordingly. WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm] RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm] Call Trace: <TASK> kvm_arch_destroy_vm+0x130/0x1b0 [kvm] kvm_destroy_vm+0x162/0x2a0 [kvm] kvm_vcpu_release+0x34/0x60 [kvm] __fput+0x82/0x240 task_work_run+0x5c/0x90 do_exit+0x364/0xa10 ? futex_unqueue+0x38/0x60 do_group_exit+0x33/0xa0 get_signal+0x155/0x850 arch_do_signal_or_restart+0xed/0x750 exit_to_user_mode_prepare+0xc5/0x120 syscall_exit_to_user_mode+0x1d/0x40 do_syscall_64+0x48/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae If kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by kvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of marking a struct page as dirty/accessed after it has been put back on the free list. This directly triggers a WARN due to encountering a page with page_count() == 0, but it can also lead to data corruption and additional errors in the kernel. WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171 RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm] Call Trace: <TASK> kvm_set_pfn_dirty+0x120/0x1d0 [kvm] __handle_changed_spte+0x92e/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] __handle_changed_spte+0x63c/0xca0 [kvm] zap_gfn_range+0x549/0x620 [kvm] kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm] mmu_free_root_page+0x219/0x2c0 [kvm] kvm_mmu_free_roots+0x1b4/0x4e0 [kvm] kvm_mmu_unload+0x1c/0xa0 [kvm] kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm] kvm_put_kvm+0x3b1/0x8b0 [kvm] kvm_vcpu_release+0x4e/0x70 [kvm] __fput+0x1f7/0x8c0 task_work_run+0xf8/0x1a0 do_exit+0x97b/0x2230 do_group_exit+0xda/0x2a0 get_signal+0x3be/0x1e50 arch_do_signal_or_restart+0x244/0x17f0 exit_to_user_mode_prepare+0xcb/0x120 syscall_exit_to_user_mode+0x1d/0x40 do_syscall_64+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae Note, the underlying bug existed even before commit 1af4a96025b3 ("KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed") moved calls to tdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still incorrectly advance past a top-level entry when yielding on a lower-level entry. But with respect to leaking shadow pages, the bug was introduced by yielding before processing the current gfn. Alternatively, tdp_mmu_iter_cond_resched() could simply fall through, or callers could jump to their "retry" label. The downside of that approach is that tdp_mmu_iter_cond_resched() _must_ be called before anything else in the loop, and there's no easy way to enfornce that requirement. Ideally, KVM would handling the cond_resched() fully within the iterator macro (the code is actually quite clean) and avoid this entire class of bugs, but that is extremely difficult do wh ---truncated---

Solution(s)

  • suse-upgrade-cluster-md-kmp-64kb
  • suse-upgrade-cluster-md-kmp-azure
  • suse-upgrade-cluster-md-kmp-default
  • suse-upgrade-cluster-md-kmp-rt
  • suse-upgrade-dlm-kmp-64kb
  • suse-upgrade-dlm-kmp-azure
  • suse-upgrade-dlm-kmp-default
  • suse-upgrade-dlm-kmp-rt
  • suse-upgrade-dtb-allwinner
  • suse-upgrade-dtb-altera
  • suse-upgrade-dtb-amazon
  • suse-upgrade-dtb-amd
  • suse-upgrade-dtb-amlogic
  • suse-upgrade-dtb-apm
  • suse-upgrade-dtb-apple
  • suse-upgrade-dtb-arm
  • suse-upgrade-dtb-broadcom
  • suse-upgrade-dtb-cavium
  • suse-upgrade-dtb-exynos
  • suse-upgrade-dtb-freescale
  • suse-upgrade-dtb-hisilicon
  • suse-upgrade-dtb-lg
  • suse-upgrade-dtb-marvell
  • suse-upgrade-dtb-mediatek
  • suse-upgrade-dtb-nvidia
  • suse-upgrade-dtb-qcom
  • suse-upgrade-dtb-renesas
  • suse-upgrade-dtb-rockchip
  • suse-upgrade-dtb-socionext
  • suse-upgrade-dtb-sprd
  • suse-upgrade-dtb-xilinx
  • suse-upgrade-gfs2-kmp-64kb
  • suse-upgrade-gfs2-kmp-azure
  • suse-upgrade-gfs2-kmp-default
  • suse-upgrade-gfs2-kmp-rt
  • suse-upgrade-kernel-64kb
  • suse-upgrade-kernel-64kb-devel
  • suse-upgrade-kernel-64kb-extra
  • suse-upgrade-kernel-64kb-livepatch-devel
  • suse-upgrade-kernel-64kb-optional
  • suse-upgrade-kernel-azure
  • suse-upgrade-kernel-azure-devel
  • suse-upgrade-kernel-azure-extra
  • suse-upgrade-kernel-azure-livepatch-devel
  • suse-upgrade-kernel-azure-optional
  • suse-upgrade-kernel-azure-vdso
  • suse-upgrade-kernel-debug
  • suse-upgrade-kernel-debug-devel
  • suse-upgrade-kernel-debug-livepatch-devel
  • suse-upgrade-kernel-debug-vdso
  • suse-upgrade-kernel-default
  • suse-upgrade-kernel-default-base
  • suse-upgrade-kernel-default-base-rebuild
  • suse-upgrade-kernel-default-devel
  • suse-upgrade-kernel-default-extra
  • suse-upgrade-kernel-default-livepatch
  • suse-upgrade-kernel-default-livepatch-devel
  • suse-upgrade-kernel-default-optional
  • suse-upgrade-kernel-default-vdso
  • suse-upgrade-kernel-devel
  • suse-upgrade-kernel-devel-azure
  • suse-upgrade-kernel-devel-rt
  • suse-upgrade-kernel-docs
  • suse-upgrade-kernel-docs-html
  • suse-upgrade-kernel-kvmsmall
  • suse-upgrade-kernel-kvmsmall-devel
  • suse-upgrade-kernel-kvmsmall-livepatch-devel
  • suse-upgrade-kernel-kvmsmall-vdso
  • suse-upgrade-kernel-macros
  • suse-upgrade-kernel-obs-build
  • suse-upgrade-kernel-obs-qa
  • suse-upgrade-kernel-rt
  • suse-upgrade-kernel-rt-devel
  • suse-upgrade-kernel-rt-extra
  • suse-upgrade-kernel-rt-livepatch
  • suse-upgrade-kernel-rt-livepatch-devel
  • suse-upgrade-kernel-rt-optional
  • suse-upgrade-kernel-rt-vdso
  • suse-upgrade-kernel-rt_debug
  • suse-upgrade-kernel-rt_debug-devel
  • suse-upgrade-kernel-rt_debug-livepatch-devel
  • suse-upgrade-kernel-rt_debug-vdso
  • suse-upgrade-kernel-source
  • suse-upgrade-kernel-source-azure
  • suse-upgrade-kernel-source-rt
  • suse-upgrade-kernel-source-vanilla
  • suse-upgrade-kernel-syms
  • suse-upgrade-kernel-syms-azure
  • suse-upgrade-kernel-syms-rt
  • suse-upgrade-kernel-zfcpdump
  • suse-upgrade-kselftests-kmp-64kb
  • suse-upgrade-kselftests-kmp-azure
  • suse-upgrade-kselftests-kmp-default
  • suse-upgrade-kselftests-kmp-rt
  • suse-upgrade-ocfs2-kmp-64kb
  • suse-upgrade-ocfs2-kmp-azure
  • suse-upgrade-ocfs2-kmp-default
  • suse-upgrade-ocfs2-kmp-rt
  • suse-upgrade-reiserfs-kmp-64kb
  • suse-upgrade-reiserfs-kmp-azure
  • suse-upgrade-reiserfs-kmp-default
  • suse-upgrade-reiserfs-kmp-rt

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