Описание
In the Linux kernel, the following vulnerability has been resolved:
KVM: Reject wrapped offset in kvm_reset_dirty_gfn()
kvm_reset_dirty_gfn() guards the gfn range with
if (!memslot || (offset + __fls(mask)) >= memslot->npages)
return;
but offset is u64 and the addition is unchecked. The check can be
silently bypassed by a u64 wrap.
The dirty ring backing those entries is MAP_SHARED at
KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the
slot and offset fields of any entry between when the kernel pushes
them and when KVM_RESET_DIRTY_RINGS consumes them. On reset,
kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds
them straight back into this check; only the flags handshake is
treated as the handover, the slot/offset payload is taken on trust.
Crafting two entries
entry[i].offset = 0xffffffffffffffc1
entry[i+1].offset = 0
makes the coalescing loop in kvm_dirty_ring_reset() compute
delta = (s64)(0 - 0xffffffffffffffc1) = 63
which falls in [0, BITS_PER_LONG), so it folds entry[i+1] into the
existing mask by setting bit 63. The trailing kvm_reset_dirty_gfn()
call then sees offset = 0xffffffffffffffc1 and __fls(mask) = 63;
the sum is 0 in u64 and the bounds check passes.
That offset propagates into kvm_arch_mmu_enable_log_dirty_pt_masked()
unchanged. On the legacy MMU path -- kvm_memslots_have_rmaps() ==
true, i.e. shadow paging, any VM that has allocated shadow roots, or
a write-tracked slot -- it reaches gfn_to_rmap(), which indexes
slot->arch.rmap[0][] with a near-U64_MAX gfn. That is an
out-of-bounds load of a kvm_rmap_head, followed by a conditional
clear of PT_WRITABLE_MASK in whatever the loaded pointer points at.
The path is reachable from any process holding /dev/kvm.
Range-check offset on its own first, so the addition cannot wrap.
memslot->npages is bounded well below U64_MAX, so once offset <
npages holds, offset + __fls(mask) (with __fls(mask) < BITS_PER_LONG)
stays in range.
A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) component. A local attacker with access to /dev/kvm could exploit an integer overflow vulnerability in the kvm_reset_dirty_gfn() function. By manipulating dirty ring entries, the attacker can bypass a bounds check, leading to an out-of-bounds memory access. This could result in information disclosure or potentially cause a denial of service.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Not affected | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Not affected |
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Дополнительная информация
Статус:
EPSS
7 High
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: KVM: Reject wrapped offset in kvm_reset_dirty_gfn() kvm_reset_dirty_gfn() guards the gfn range with if (!memslot || (offset + __fls(mask)) >= memslot->npages) return; but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap. The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust. Crafting two entries entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0 makes the coalescing loop in kvm_dirty_ring_reset() compute delta = (s64)(0 - 0xffffffffffffffc1) = 63 which falls in [0, BITS_...
In the Linux kernel, the following vulnerability has been resolved: KVM: Reject wrapped offset in kvm_reset_dirty_gfn() kvm_reset_dirty_gfn() guards the gfn range with if (!memslot || (offset + __fls(mask)) >= memslot->npages) return; but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap. The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust. Crafting two entries entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0 makes the coalescing loop in kvm_dirty_ring_reset() compute delta = (s64)(0 - 0xffffffffffffffc1) = 63 which falls
In the Linux kernel, the following vulnerability has been resolved: K ...
In the Linux kernel, the following vulnerability has been resolved: KVM: Reject wrapped offset in kvm_reset_dirty_gfn() kvm_reset_dirty_gfn() guards the gfn range with if (!memslot || (offset + __fls(mask)) >= memslot->npages) return; but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap. The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust. Crafting two entries entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0 makes the coalescing loop in kvm_dirty_ring_reset() compute delta = (s64)(0 - 0xffffffffffffffc1) = 63 which fa...
EPSS
7 High
CVSS3