CVE 설명

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Use active memslots for the per-vCPU MMIO cache KVM tags the per-vCPU MMIO cache with a memslot generation so that a memslot update invalidates cached MMIO information. Both the fill and validation paths use kvm_memslots(), which unconditionally selects address space 0, even when the vCPU is running in SMM and using address space 1. Commit 56f17dd3fbc4 ("kvm: x86: fix stale mmio cache bug") added the memslot generation to the cache key so that a memslot update could not leave a stale entry valid. When commit 699023e23965 ("KVM: x86: add SMM to the MMU role, support SMRAM address space") added the SMM address space, these helpers were not converted to use the active memslots. Consequently, an update to the SMM memslots can leave an entry from the old SMM address space apparently valid after the vCPU returns to the normal address space. A guest can then cause an access to valid RAM at the same GFN to be returned to userspace as KVM_EXIT_MMIO. Completing that exit through the VMM's RAM address space writes the backing page without going through KVM's write-tracking path. If the page backs a nested EPT table, KVM can continue using shadow translations derived from the old contents. The WARN_ON_ONCE() in kvm_mmu_write_protect_fault() catches this invalid cache and memslot combination. Use the vCPU's active memslots when caching and validating the entry. Memslot generations are unique across address spaces, so the generation also distinguishes the normal and SMM views. This matches the MMIO SPTE cache, which already uses kvm_vcpu_memslots(). On an unpatched current-mainline kernel, a regression test that fills the cache in SMM and updates only the SMM memslots fails the intended RAM write and triggers the kvm_mmu_write_protect_fault() warning. With this change, the same test completes the RAM write without a warning. The x86/smm_test, set_memory_region_test, and memslot_modification_stress_test selftests also pass.

CVE 정보

메트릭

메트릭	점수	심각도	CVSS 벡터	출처
V3.1	8.8	HIGH	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H 추가 정보 Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Local The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. Changed An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities. Base: Impact Metrics The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental Metrics These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.	416baaa9-dc9f-4396-8d5f-8c081fb06d67