{
  "gsd": {
    "metadata": {
      "exploitCode": "unknown",
      "remediation": "unknown",
      "reportConfidence": "confirmed",
      "type": "vulnerability"
    },
    "osvSchema": {
      "aliases": [
        "CVE-2021-47094"
      ],
      "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don\u0027t advance iterator after restart due to yielding\n\nAfter dropping mmu_lock in the TDP MMU, restart the iterator during\ntdp_iter_next() and do not advance the iterator.  Advancing the iterator\nresults in skipping the top-level SPTE and all its children, which is\nfatal if any of the skipped SPTEs were not visited before yielding.\n\nWhen zapping all SPTEs, i.e. when min_level == root_level, restarting the\niter and then invoking tdp_iter_next() is always fatal if the current gfn\nhas as a valid SPTE, as advancing the iterator results in try_step_side()\nskipping the current gfn, which wasn\u0027t visited before yielding.\n\nSprinkle WARNs on iter-\u003eyielded being true in various helpers that are\noften used in conjunction with yielding, and tag the helper with\n__must_check to reduce the probabily of improper usage.\n\nFailing to zap a top-level SPTE manifests in one of two ways.  If a valid\nSPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),\nthe shadow page will be leaked and KVM will WARN accordingly.\n\n  WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]\n  RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_arch_destroy_vm+0x130/0x1b0 [kvm]\n   kvm_destroy_vm+0x162/0x2a0 [kvm]\n   kvm_vcpu_release+0x34/0x60 [kvm]\n   __fput+0x82/0x240\n   task_work_run+0x5c/0x90\n   do_exit+0x364/0xa10\n   ? futex_unqueue+0x38/0x60\n   do_group_exit+0x33/0xa0\n   get_signal+0x155/0x850\n   arch_do_signal_or_restart+0xed/0x750\n   exit_to_user_mode_prepare+0xc5/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x48/0xc0\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nIf kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by\nkvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of\nmarking a struct page as dirty/accessed after it has been put back on the\nfree list.  This directly triggers a WARN due to encountering a page with\npage_count() == 0, but it can also lead to data corruption and additional\nerrors in the kernel.\n\n  WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171\n  RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_set_pfn_dirty+0x120/0x1d0 [kvm]\n   __handle_changed_spte+0x92e/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   zap_gfn_range+0x549/0x620 [kvm]\n   kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]\n   mmu_free_root_page+0x219/0x2c0 [kvm]\n   kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]\n   kvm_mmu_unload+0x1c/0xa0 [kvm]\n   kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]\n   kvm_put_kvm+0x3b1/0x8b0 [kvm]\n   kvm_vcpu_release+0x4e/0x70 [kvm]\n   __fput+0x1f7/0x8c0\n   task_work_run+0xf8/0x1a0\n   do_exit+0x97b/0x2230\n   do_group_exit+0xda/0x2a0\n   get_signal+0x3be/0x1e50\n   arch_do_signal_or_restart+0x244/0x17f0\n   exit_to_user_mode_prepare+0xcb/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x4d/0x90\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nNote, the underlying bug existed even before commit 1af4a96025b3 (\"KVM:\nx86/mmu: Yield in TDU MMU iter even if no SPTES changed\") moved calls to\ntdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still\nincorrectly advance past a top-level entry when yielding on a lower-level\nentry.  But with respect to leaking shadow pages, the bug was introduced\nby yielding before processing the current gfn.\n\nAlternatively, tdp_mmu_iter_cond_resched() could simply fall through, or\ncallers could jump to their \"retry\" label.  The downside of that approach\nis that tdp_mmu_iter_cond_resched() _must_ be called before anything else\nin the loop, and there\u0027s no easy way to enfornce that requirement.\n\nIdeally, KVM would handling the cond_resched() fully within the iterator\nmacro (the code is actually quite clean) and avoid this entire class of\nbugs, but that is extremely difficult do wh\n---truncated---",
      "id": "GSD-2021-47094",
      "modified": "2024-03-01T06:04:48.349009Z",
      "schema_version": "1.4.0"
    }
  },
  "namespaces": {
    "cve.org": {
      "CVE_data_meta": {
        "ASSIGNER": "cve@kernel.org",
        "ID": "CVE-2021-47094",
        "STATE": "PUBLIC"
      },
      "affects": {
        "vendor": {
          "vendor_data": [
            {
              "product": {
                "product_data": [
                  {
                    "product_name": "Linux",
                    "version": {
                      "version_data": [
                        {
                          "version_affected": "\u003c",
                          "version_name": "faaf05b00aec",
                          "version_value": "d884eefd75cc"
                        },
                        {
                          "version_value": "not down converted",
                          "x_cve_json_5_version_data": {
                            "defaultStatus": "affected",
                            "versions": [
                              {
                                "status": "affected",
                                "version": "5.10"
                              },
                              {
                                "lessThan": "5.10",
                                "status": "unaffected",
                                "version": "0",
                                "versionType": "custom"
                              },
                              {
                                "lessThanOrEqual": "5.15.*",
                                "status": "unaffected",
                                "version": "5.15.12",
                                "versionType": "custom"
                              },
                              {
                                "lessThanOrEqual": "*",
                                "status": "unaffected",
                                "version": "5.16",
                                "versionType": "original_commit_for_fix"
                              }
                            ]
                          }
                        }
                      ]
                    }
                  }
                ]
              },
              "vendor_name": "Linux"
            }
          ]
        }
      },
      "data_format": "MITRE",
      "data_type": "CVE",
      "data_version": "4.0",
      "description": {
        "description_data": [
          {
            "lang": "eng",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don\u0027t advance iterator after restart due to yielding\n\nAfter dropping mmu_lock in the TDP MMU, restart the iterator during\ntdp_iter_next() and do not advance the iterator.  Advancing the iterator\nresults in skipping the top-level SPTE and all its children, which is\nfatal if any of the skipped SPTEs were not visited before yielding.\n\nWhen zapping all SPTEs, i.e. when min_level == root_level, restarting the\niter and then invoking tdp_iter_next() is always fatal if the current gfn\nhas as a valid SPTE, as advancing the iterator results in try_step_side()\nskipping the current gfn, which wasn\u0027t visited before yielding.\n\nSprinkle WARNs on iter-\u003eyielded being true in various helpers that are\noften used in conjunction with yielding, and tag the helper with\n__must_check to reduce the probabily of improper usage.\n\nFailing to zap a top-level SPTE manifests in one of two ways.  If a valid\nSPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),\nthe shadow page will be leaked and KVM will WARN accordingly.\n\n  WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]\n  RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_arch_destroy_vm+0x130/0x1b0 [kvm]\n   kvm_destroy_vm+0x162/0x2a0 [kvm]\n   kvm_vcpu_release+0x34/0x60 [kvm]\n   __fput+0x82/0x240\n   task_work_run+0x5c/0x90\n   do_exit+0x364/0xa10\n   ? futex_unqueue+0x38/0x60\n   do_group_exit+0x33/0xa0\n   get_signal+0x155/0x850\n   arch_do_signal_or_restart+0xed/0x750\n   exit_to_user_mode_prepare+0xc5/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x48/0xc0\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nIf kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by\nkvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of\nmarking a struct page as dirty/accessed after it has been put back on the\nfree list.  This directly triggers a WARN due to encountering a page with\npage_count() == 0, but it can also lead to data corruption and additional\nerrors in the kernel.\n\n  WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171\n  RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_set_pfn_dirty+0x120/0x1d0 [kvm]\n   __handle_changed_spte+0x92e/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   zap_gfn_range+0x549/0x620 [kvm]\n   kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]\n   mmu_free_root_page+0x219/0x2c0 [kvm]\n   kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]\n   kvm_mmu_unload+0x1c/0xa0 [kvm]\n   kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]\n   kvm_put_kvm+0x3b1/0x8b0 [kvm]\n   kvm_vcpu_release+0x4e/0x70 [kvm]\n   __fput+0x1f7/0x8c0\n   task_work_run+0xf8/0x1a0\n   do_exit+0x97b/0x2230\n   do_group_exit+0xda/0x2a0\n   get_signal+0x3be/0x1e50\n   arch_do_signal_or_restart+0x244/0x17f0\n   exit_to_user_mode_prepare+0xcb/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x4d/0x90\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nNote, the underlying bug existed even before commit 1af4a96025b3 (\"KVM:\nx86/mmu: Yield in TDU MMU iter even if no SPTES changed\") moved calls to\ntdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still\nincorrectly advance past a top-level entry when yielding on a lower-level\nentry.  But with respect to leaking shadow pages, the bug was introduced\nby yielding before processing the current gfn.\n\nAlternatively, tdp_mmu_iter_cond_resched() could simply fall through, or\ncallers could jump to their \"retry\" label.  The downside of that approach\nis that tdp_mmu_iter_cond_resched() _must_ be called before anything else\nin the loop, and there\u0027s no easy way to enfornce that requirement.\n\nIdeally, KVM would handling the cond_resched() fully within the iterator\nmacro (the code is actually quite clean) and avoid this entire class of\nbugs, but that is extremely difficult do wh\n---truncated---"
          }
        ]
      },
      "generator": {
        "engine": "bippy-5f0117140d9a"
      },
      "problemtype": {
        "problemtype_data": [
          {
            "description": [
              {
                "lang": "eng",
                "value": "n/a"
              }
            ]
          }
        ]
      },
      "references": {
        "reference_data": [
          {
            "name": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c",
            "refsource": "MISC",
            "url": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c"
          },
          {
            "name": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c",
            "refsource": "MISC",
            "url": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c"
          }
        ]
      }
    },
    "nvd.nist.gov": {
      "cve": {
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don\u0027t advance iterator after restart due to yielding\n\nAfter dropping mmu_lock in the TDP MMU, restart the iterator during\ntdp_iter_next() and do not advance the iterator.  Advancing the iterator\nresults in skipping the top-level SPTE and all its children, which is\nfatal if any of the skipped SPTEs were not visited before yielding.\n\nWhen zapping all SPTEs, i.e. when min_level == root_level, restarting the\niter and then invoking tdp_iter_next() is always fatal if the current gfn\nhas as a valid SPTE, as advancing the iterator results in try_step_side()\nskipping the current gfn, which wasn\u0027t visited before yielding.\n\nSprinkle WARNs on iter-\u003eyielded being true in various helpers that are\noften used in conjunction with yielding, and tag the helper with\n__must_check to reduce the probabily of improper usage.\n\nFailing to zap a top-level SPTE manifests in one of two ways.  If a valid\nSPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),\nthe shadow page will be leaked and KVM will WARN accordingly.\n\n  WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]\n  RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_arch_destroy_vm+0x130/0x1b0 [kvm]\n   kvm_destroy_vm+0x162/0x2a0 [kvm]\n   kvm_vcpu_release+0x34/0x60 [kvm]\n   __fput+0x82/0x240\n   task_work_run+0x5c/0x90\n   do_exit+0x364/0xa10\n   ? futex_unqueue+0x38/0x60\n   do_group_exit+0x33/0xa0\n   get_signal+0x155/0x850\n   arch_do_signal_or_restart+0xed/0x750\n   exit_to_user_mode_prepare+0xc5/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x48/0xc0\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nIf kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by\nkvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of\nmarking a struct page as dirty/accessed after it has been put back on the\nfree list.  This directly triggers a WARN due to encountering a page with\npage_count() == 0, but it can also lead to data corruption and additional\nerrors in the kernel.\n\n  WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171\n  RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_set_pfn_dirty+0x120/0x1d0 [kvm]\n   __handle_changed_spte+0x92e/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   zap_gfn_range+0x549/0x620 [kvm]\n   kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]\n   mmu_free_root_page+0x219/0x2c0 [kvm]\n   kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]\n   kvm_mmu_unload+0x1c/0xa0 [kvm]\n   kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]\n   kvm_put_kvm+0x3b1/0x8b0 [kvm]\n   kvm_vcpu_release+0x4e/0x70 [kvm]\n   __fput+0x1f7/0x8c0\n   task_work_run+0xf8/0x1a0\n   do_exit+0x97b/0x2230\n   do_group_exit+0xda/0x2a0\n   get_signal+0x3be/0x1e50\n   arch_do_signal_or_restart+0x244/0x17f0\n   exit_to_user_mode_prepare+0xcb/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x4d/0x90\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nNote, the underlying bug existed even before commit 1af4a96025b3 (\"KVM:\nx86/mmu: Yield in TDU MMU iter even if no SPTES changed\") moved calls to\ntdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still\nincorrectly advance past a top-level entry when yielding on a lower-level\nentry.  But with respect to leaking shadow pages, the bug was introduced\nby yielding before processing the current gfn.\n\nAlternatively, tdp_mmu_iter_cond_resched() could simply fall through, or\ncallers could jump to their \"retry\" label.  The downside of that approach\nis that tdp_mmu_iter_cond_resched() _must_ be called before anything else\nin the loop, and there\u0027s no easy way to enfornce that requirement.\n\nIdeally, KVM would handling the cond_resched() fully within the iterator\nmacro (the code is actually quite clean) and avoid this entire class of\nbugs, but that is extremely difficult do wh\n---truncated---"
          }
        ],
        "id": "CVE-2021-47094",
        "lastModified": "2024-03-05T13:41:01.900",
        "metrics": {},
        "published": "2024-03-04T18:15:07.837",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/3a0f64de479cae75effb630a2e0a237ca0d0623c"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/d884eefd75cc54887bc2e9e724207443525dfb2c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Awaiting Analysis"
      }
    }
  }
}