CVE-2026-63806

*** Pendiente de traducción *** In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned()<br /> <br /> Drop a BUG_ON() that has been reachable since it was first added, way back<br /> in 2009, and instead use get_unaligned() to perform potentially-unaligned<br /> accesses.<br /> <br /> For a given store, KVM x86&amp;#39;s emulator tracks the entire value in the<br /> destination operand, x86_emulate_ctxt.dst. If the destination is memory,<br /> and the target splits multiple pages and/or is emulated MMIO, then KVM<br /> handles each fragment independently. E.g. on a page split starting at page<br /> offset 0xffc, KVM writes 4 bytes to the first page, then the remaining<br /> bytes to the second page, using ctxt-&gt;dst as the source for both (with<br /> appropriate offsets).<br /> <br /> If the destination splits a page *and* hits emulated MMIO on the second<br /> page, then KVM will complete the write to the first page, then emulate the<br /> MMIO access to the second page. If there is a datamatch-enabled ioeventfd<br /> at offset 0 of the second page, then KVM will process the remainder of the<br /> store as a potential ioeventfd signal.<br /> <br /> Putting it all together, if the guest emits a store that splits a page<br /> starting at page offset N, and the second page has a datamatch-enabled<br /> ioeventfd at offset 0, then KVM will check for datamatch using<br /> &amp;dst.valptr[N] as the source. Due to dst (and thus dst.valptr) being<br /> 32-byte aligned, if N is not aligned to @len, the BUG_ON() fires.<br /> <br /> E.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8,<br /> all initial checks in ioeventfd_in_range() will succeed, and the BUG_ON()<br /> fires due to @val being 4-byte aligned, but not 8-byte aligned.<br /> <br /> ------------[ cut here ]------------<br /> kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783!<br /> Oops: invalid opcode: 0000 [#1] SMP<br /> CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT<br /> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015<br /> RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm]<br /> Call Trace:<br /> <br /> __kvm_io_bus_write+0x85/0xb0 [kvm]<br /> kvm_io_bus_write+0x53/0x80 [kvm]<br /> vcpu_mmio_write+0x66/0xf0 [kvm]<br /> emulator_read_write_onepage+0x12a/0x540 [kvm]<br /> emulator_read_write+0x109/0x2b0 [kvm]<br /> x86_emulate_insn+0x4f8/0xfb0 [kvm]<br /> x86_emulate_instruction+0x181/0x790 [kvm]<br /> kvm_mmu_page_fault+0x313/0x630 [kvm]<br /> vmx_handle_exit+0x18a/0x590 [kvm_intel]<br /> kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm]<br /> kvm_vcpu_ioctl+0x2d5/0x970 [kvm]<br /> __x64_sys_ioctl+0x8a/0xd0<br /> do_syscall_64+0xb7/0x890<br /> entry_SYSCALL_64_after_hwframe+0x4b/0x53<br /> RIP: 0033:0x7f19c931a9bf<br /> <br /> Modules linked in: kvm_intel kvm irqbypass<br /> ---[ end trace 0000000000000000 ]---<br /> <br /> In a perfect world, the fix would be to simply delete the BUG_ON(), as KVM<br /> x86 doesn&amp;#39;t perform alignment checks on "normal" memory accesses at CPL0.<br /> Sadly, C99 ruins all the fun; while the x86 architecture plays nice,<br /> dereferencing an unaligned pointer directly is undefined behavior in C,<br /> e.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.