{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-40953", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-40953" ], "published": "2024-07-12T12:32:42Z", "summary": "KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin()", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin()\n\nUse {READ,WRITE}_ONCE() to access kvm->last_boosted_vcpu to ensure the\nloads and stores are atomic. In the extremely unlikely scenario the\ncompiler tears the stores, it's theoretically possible for KVM to attempt\nto get a vCPU using an out-of-bounds index, e.g. if the write is split\ninto multiple 8-bit stores, and is paired with a 32-bit load on a VM with\n257 vCPUs:\n\n CPU0 CPU1\n last_boosted_vcpu = 0xff;\n\n (last_boosted_vcpu = 0x100)\n last_boosted_vcpu[15:8] = 0x01;\n i = (last_boosted_vcpu = 0x1ff)\n last_boosted_vcpu[7:0] = 0x00;\n\n vcpu = kvm->vcpu_array[0x1ff];\n\nAs detected by KCSAN:\n\n BUG: KCSAN: data-race in kvm_vcpu_on_spin [kvm] / kvm_vcpu_on_spin [kvm]\n\n write to 0xffffc90025a92344 of 4 bytes by task 4340 on cpu 16:\n kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112) kvm\n handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel\n vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?\n\t\t arch/x86/kvm/vmx/vmx.c:6606) kvm_intel\n vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm\n kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm\n kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm\n __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)\n __x64_sys_ioctl (fs/ioctl.c:890)\n x64_sys_call (arch/x86/entry/syscall_64.c:33)\n do_syscall_64 (arch/x86/entry/common.c:?)\n entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n\n read to 0xffffc90025a92344 of 4 bytes by task 4342 on cpu 4:\n kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4069) kvm\n handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel\n vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?\n\t\t\tarch/x86/kvm/vmx/vmx.c:6606) kvm_intel\n vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm\n kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm\n kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm\n __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)\n __x64_sys_ioctl (fs/ioctl.c:890)\n x64_sys_call (arch/x86/entry/syscall_64.c:33)\n do_syscall_64 (arch/x86/entry/common.c:?)\n entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n\n value changed: 0x00000012 -> 0x00000000", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.21-1+rpt1", "1:6.1.47-1+rpt2", "1:6.1.47-1+rpt4", "1:6.1.54-1+rpt2", "1:6.1.58-1+rpt2", "1:6.1.63-1+rpt1", "1:6.1.73-1+rpt1", "1:6.6.20-1+rpt1", "1:6.6.28-1+rpt1", "1:6.6.31-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi1-rpi-v8", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v8", "binary_version": "1:6.1.47-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi4-rpi-2712", "binary_version": "1:6.1.54-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi4-rpi-v8", "binary_version": "1:6.1.54-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi6-rpi-2712", "binary_version": "1:6.1.58-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi6-rpi-v8", "binary_version": "1:6.1.58-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi7-rpi-2712", "binary_version": "1:6.1.63-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi7-rpi-v8", "binary_version": "1:6.1.63-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi8-rpi-2712", "binary_version": "1:6.1.73-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi8-rpi-v8", "binary_version": "1:6.1.73-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-2712", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-v8", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.28+rpt-rpi-2712", "binary_version": "1:6.6.28-1+rpt1" }, { "binary_name": "linux-image-6.6.28+rpt-rpi-v8", "binary_version": "1:6.6.28-1+rpt1" }, { "binary_name": "linux-image-6.6.31+rpt-rpi-2712", "binary_version": "1:6.6.31-1+rpt1" }, { "binary_name": "linux-image-6.6.31+rpt-rpi-v8", "binary_version": "1:6.6.31-1+rpt1" } ] }, "database_specific": { "per_version": { "1:6.1.21-1+rpt1": { "linux_commit": "0afb5e98488aed7017b9bf321b575d0177feb7ed", "upstream_version": "6.1.21", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.96" }, "1:6.1.47-1+rpt2": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.96" }, "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.96", "compiled_filter": false }, "1:6.1.54-1+rpt2": { "linux_commit": "2906f7abdc03d4a92b6b0e2e0c87ea2a9dffe8f7", "upstream_version": "6.1.54", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.96" }, "1:6.1.58-1+rpt2": { "linux_commit": "ccf1586ad0663fa91238ac56abf6340d6d740d18", "upstream_version": "6.1.58", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.96" }, "1:6.1.63-1+rpt1": { "linux_commit": null, "upstream_version": "6.1.63", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.96" }, "1:6.1.73-1+rpt1": { "linux_commit": null, "upstream_version": "6.1.73", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.96" }, "1:6.6.20-1+rpt1": { "linux_commit": "6f16847710cc0502450788b9f12f0a14d3429668", "upstream_version": "6.6.20", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.36" }, "1:6.6.28-1+rpt1": { "linux_commit": "0c341f47adc3578cd5f817aa20ee2b7f9ae6b23e", "upstream_version": "6.6.28", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.36" }, "1:6.6.31-1+rpt1": { "linux_commit": "c1432b4bae5b6582f4d32ba381459f33c34d1424", "upstream_version": "6.6.31", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.36" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2024-40953" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/11a772d5376aa6d3e2e69b5b5c585f79b60c0e17" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/4c141136a28421b78f34969b25a4fa32e06e2180" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/71fbc3af3dacb26c3aa2f30bb3ab05c44d082c84" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/82bd728a06e55f5b5f93d10ce67f4fe7e689853a" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/92c77807d938145c7c3350c944ef9f39d7f6017c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/a937ef951bba72f48d2402451419d725d70dba20" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/95c8dd79f3a14df96b3820b35b8399bd91b2be60" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/49f683b41f28918df3e51ddc0d928cb2e934ccdb" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T11:52:36Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.9, "cvss_v3_severity": "High", "scenario": "AV:L - The vulnerable code is entered only from guest execution of PAUSE/WFE/DIAG-0x44 handled by the host KVM module, or equivalently via the `KVM_RUN` ioctl on `/dev/kvm` as shown in the KCSAN stack trace. There is no network-facing path to `kvm_vcpu_on_spin()`, so the attacker must be running code locally on the host or inside a VM hosted on it.\nAC:L - The attacker controls both sides of the race outright \u2014 a guest simply runs PAUSE spin loops on several vCPUs at once, driving many threads into the unsynchronized read/write of `kvm->last_boosted_vcpu` with no external precondition. No specific victim state or memory layout the attacker cannot influence is required to hit the racing accesses.\nPR:L - The attacker needs the ability to run code inside a VM on the host (or open `/dev/kvm` locally), which is an unprivileged-user-level capability \u2014 no root or CAP_SYS_ADMIN is required, and PAUSE is executable from guest ring 3. This matches the standard treatment of guest-triggerable KVM host bugs.\nUI:N - Triggering requires only that the attacker's own guest vCPU threads spin concurrently; no host administrator or other user has to perform any action. The race is hit entirely by the attacker's own execution.\nS:C - The bug is triggered by unprivileged code inside a guest but the corrupted index and any resulting wild pointer access occur in the host kernel, crossing the VM-to-hypervisor security boundary. A guest compromising host kernel availability/integrity is a scope change.\nC:L - A torn value yields an out-of-bounds vCPU index, causing the host to read a pointer-sized slot past the vCPU array and then dereference it (`vcpu->ready`, `vcpu->preempted`, `target->pid`), touching host kernel memory outside the intended object. The read value is never returned to the guest and the offset is not attacker-chosen, so this is a limited disclosure rather than an arbitrary read primitive.\nI:L - `kvm_vcpu_eligible_for_directed_yield()` writes `vcpu->spin_loop.dy_eligible` through the same unvalidated pointer, giving a fixed-offset host-kernel write via an out-of-bounds vCPU reference, and the bogus target also perturbs host scheduling through `yield_to()`. The written value and target address are not attacker-controlled, limiting this to bounded corruption rather than a control-flow hijack primitive.\nA:H - Per the upstream changelog, the torn access lets KVM fetch a vCPU with an out-of-bounds index; the resulting NULL or garbage pointer is dereferenced without any validation, oopsing or panicking the host kernel. A guest crashing the hypervisor takes down the host and every other VM on it." } } }