{"dataType":"CVE_RECORD","dataVersion":"5.1","cveMetadata":{"cveId":"CVE-2021-47465","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-05-22T06:20:56.198Z","datePublished":"2024-05-22T06:23:25.027Z","dateUpdated":"2025-05-04T07:11:29.563Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2025-05-04T07:11:29.563Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()\n\nIn commit 10d91611f426 (\"powerpc/64s: Reimplement book3s idle code in\nC\") kvm_start_guest() became idle_kvm_start_guest(). The old code\nallocated a stack frame on the emergency stack, but didn't use the\nframe to store anything, and also didn't store anything in its caller's\nframe.\n\nidle_kvm_start_guest() on the other hand is written more like a normal C\nfunction, it creates a frame on entry, and also stores CR/LR into its\ncallers frame (per the ABI). The problem is that there is no caller\nframe on the emergency stack.\n\nThe emergency stack for a given CPU is allocated with:\n\n  paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;\n\nSo emergency_sp actually points to the first address above the emergency\nstack allocation for a given CPU, we must not store above it without\nfirst decrementing it to create a frame. This is different to the\nregular kernel stack, paca->kstack, which is initialised to point at an\ninitial frame that is ready to use.\n\nidle_kvm_start_guest() stores the backchain, CR and LR all of which\nwrite outside the allocation for the emergency stack. It then creates a\nstack frame and saves the non-volatile registers. Unfortunately the\nframe it creates is not large enough to fit the non-volatiles, and so\nthe saving of the non-volatile registers also writes outside the\nemergency stack allocation.\n\nThe end result is that we corrupt whatever is at 0-24 bytes, and 112-248\nbytes above the emergency stack allocation.\n\nIn practice this has gone unnoticed because the memory immediately above\nthe emergency stack happens to be used for other stack allocations,\neither another CPUs mc_emergency_sp or an IRQ stack. See the order of\ncalls to irqstack_early_init() and emergency_stack_init().\n\nThe low addresses of another stack are the top of that stack, and so are\nonly used if that stack is under extreme pressue, which essentially\nnever happens in practice - and if it did there's a high likelyhood we'd\ncrash due to that stack overflowing.\n\nStill, we shouldn't be corrupting someone else's stack, and it is purely\nluck that we aren't corrupting something else.\n\nTo fix it we save CR/LR into the caller's frame using the existing r1 on\nentry, we then create a SWITCH_FRAME_SIZE frame (which has space for\npt_regs) on the emergency stack with the backchain pointing to the\nexisting stack, and then finally we switch to the new frame on the\nemergency stack."}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kvm/book3s_hv_rmhandlers.S"],"versions":[{"version":"10d91611f426d4bafd2a83d966c36da811b2f7ad","lessThan":"80bbb0bc3a0288442f7fe6fc514f4ee1cb06ccb7","status":"affected","versionType":"git"},{"version":"10d91611f426d4bafd2a83d966c36da811b2f7ad","lessThan":"fbd724c49bead048ae9fc1a5b7bff2fb3e54f855","status":"affected","versionType":"git"},{"version":"10d91611f426d4bafd2a83d966c36da811b2f7ad","lessThan":"6d077c37c4643394b1bae9682da48164fc147ea8","status":"affected","versionType":"git"},{"version":"10d91611f426d4bafd2a83d966c36da811b2f7ad","lessThan":"9b4416c5095c20e110c82ae602c254099b83b72f","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/kvm/book3s_hv_rmhandlers.S"],"versions":[{"version":"5.2","status":"affected"},{"version":"0","lessThan":"5.2","status":"unaffected","versionType":"semver"},{"version":"5.4.156","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.76","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.14.15","lessThanOrEqual":"5.14.*","status":"unaffected","versionType":"semver"},{"version":"5.15","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.2","versionEndExcluding":"5.4.156"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.2","versionEndExcluding":"5.10.76"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.2","versionEndExcluding":"5.14.15"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.2","versionEndExcluding":"5.15"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/80bbb0bc3a0288442f7fe6fc514f4ee1cb06ccb7"},{"url":"https://git.kernel.org/stable/c/fbd724c49bead048ae9fc1a5b7bff2fb3e54f855"},{"url":"https://git.kernel.org/stable/c/6d077c37c4643394b1bae9682da48164fc147ea8"},{"url":"https://git.kernel.org/stable/c/9b4416c5095c20e110c82ae602c254099b83b72f"}],"title":"KVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()","x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"problemTypes":[{"descriptions":[{"type":"CWE","lang":"en","description":"CWE-noinfo Not enough information"}]}],"metrics":[{"cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":7.1,"attackVector":"LOCAL","baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H","integrityImpact":"HIGH","userInteraction":"NONE","attackComplexity":"LOW","availabilityImpact":"HIGH","privilegesRequired":"LOW","confidentialityImpact":"NONE"}},{"other":{"type":"ssvc","content":{"timestamp":"2024-05-29T18:41:27.701748Z","id":"CVE-2021-47465","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2024-11-07T14:41:05.510Z"}},{"providerMetadata":{"orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE","dateUpdated":"2024-08-04T05:39:59.601Z"},"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/80bbb0bc3a0288442f7fe6fc514f4ee1cb06ccb7","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/fbd724c49bead048ae9fc1a5b7bff2fb3e54f855","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/6d077c37c4643394b1bae9682da48164fc147ea8","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/9b4416c5095c20e110c82ae602c254099b83b72f","tags":["x_transferred"]}]}]}}