Threats Tagged 'cve-2026-53360'

This is a kernel live patch module which can be loaded by the kpatch command line utility to modify the code of a running kernel. This patch module is targeted for kernel-5.14.0-284.117.1.el9_2. Security Fix(es): * kernel: KVM: x86: Fix shadow paging use-after-free due to unexpected role (CVE-2026-53359) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

A vulnerability in the Linux kernel's KVM SEV implementation allows a malicious SEV-SNP guest to perform out-of-bounds reads and writes on the host kernel heap. This occurs due to improper validation of guest-controlled buffer sizes and entry indices when handling GHCB v2+ scratch areas, leading to heap corruption and information disclosure. The flaw enables leaking host heap layout information and potentially triggering use-after-free conditions. The vulnerability has been resolved in the Linux kernel.

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Fix shadow paging use-after-free due to unexpected role Commit 0cb2af2ea66ad ("KVM: x86: Fix shadow paging use-after-free due to unexpected GFN") fixed a shadow paging mismatch between stored and computed GFNs; the bug could be triggered by changing a PDE mapping from outside the guest, and then deleting a memslot. The rmap_remove() call would miss entries created after the PDE change because the GFN of the leaf SPTE does not match the GFN of the struct kvm_mmu_page. A similar hole however remains if the modified PDE points to a non-leaf page. In this case the gfn can be made to match, but the role does not match: the original large 2MB page creates a kvm_mmu_page with direct=1, while the new 4KB needs a kvm_mmu_page with direct=0. However, kvm_mmu_get_child_sp() does not compare the role, and therefore reuses the page. The next step is installing a leaf (4KB) SPTE on the new path which records an rmap entry under the gfn resolved by the walk. But when that child is zapped its parent kvm_mmu_page has direct=1 and kvm_mmu_page_get_gfn() computes the gfn for the 4KB page as sp->gfn + index instead of using sp->shadowed_translation[] (or sp->gfns[] in older kernels). It therefore fails to remove the recorded entry. When the memslot is dropped the shadow page is freed but the rmap entry survives, as in the scenario that was already fixed. Code that later walks that gfn (dirty logging, MMU notifier invalidation, and so on) dereferences an sptep that lies in the freed page, causing the use-after-free.

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use As per the GHCB spec, when using GHCB v2+ require the software scratch area to reside in the GHCB's shared buffer. Note, things like Page State Change (PSC) requests _rely_ on this behavior, as the guest can't provide a length when making the request, i.e. the size of the guest payload is bounded by the size of the shared buffer. Failure to force usage of the GHCB, and a slew of other flaws, lets a malicious SNP guest corrupt host kernel heap memory, and leak host heap layout information. setup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2), where exit_info_2 is guest-controlled. With exit_info_2=24, this yields a 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer holds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only entries[0] and entries[1] are in-bounds. snp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253) but NOT against the actual buffer size: idx_end = hdr->end_entry; if (idx_end >= VMGEXIT_PSC_MAX_COUNT) { // checks 253, not buffer snp_complete_psc(svm, ...); return 1; } for (idx = idx_start; idx <= idx_end; idx++) { entry_start = entries[idx]; // OOB when idx >= 2 The guest sets end_entry=10+, causing the host to iterate entries[2+] which are OOB into adjacent slab objects. For each OOB entry: - The host reads 8 bytes (OOB READ / info leak oracle) - If the data passes PSC validation, __snp_complete_one_psc() writes cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806) - If validation fails, the error response reveals whether adjacent memory is zero vs non-zero (information disclosure to guest) The guest controls allocation size (exit_info_2), entry range (cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly hit different slab positions. By exploiting the variety of bugs, a malicious SEV-SNP guest can: - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure) - OOB write cur_page bits into adjacent objects (heap corruption) - Trigger use-after-free conditions across VMGEXITs E.g. with KASAN enabled, a single insmod of the PoC guest module produces 73 KASAN reports: BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890 Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199 BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890 Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199 The buggy address belongs to the object at ffff888XXXXXXXXX which belongs to the cache kmalloc-cg-32 of size 32 The buggy address is located N bytes to the right of allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX) Breakdown: 62 slab-out-of-bounds (reads + writes past allocation) 7 slab-use-after-free 4 use-after-free All credit to Stan for the wonderful description and reproducer! [sean: write changelog]