{ "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": "2024-08-04T05:39:59.601Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2024-05-29T05:08:24.817Z" }, "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": "10d91611f426", "lessThan": "80bbb0bc3a02", "status": "affected", "versionType": "git" }, { "version": "10d91611f426", "lessThan": "fbd724c49bea", "status": "affected", "versionType": "git" }, { "version": "10d91611f426", "lessThan": "6d077c37c464", "status": "affected", "versionType": "git" }, { "version": "10d91611f426", "lessThan": "9b4416c5095c", "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": "custom" }, { "version": "5.4.156", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.10.76", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.14.15", "lessThanOrEqual": "5.14.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.15", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "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-a5840b7849dd" } }, "adp": [ { "title": "CISA ADP Vulnrichment", "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2021-47465", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2024-05-29T18:41:27.701748Z" } } } ], "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-06-04T17:14:10.403Z" } }, { "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" ] } ] } ] } }