commit 577a8d3bae0531f0e5ccfac919cd8192f920a804 upstream.
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.
Fixes: fb04a1eddb1a ("KVM: X86: Implement ring-based dirty memory tracking")
Cc: stable@vger.kernel.org
Signed-off-by: Aaron Sacks <contact@xchglabs.com>
Link: https://patch.msgid.link/20260512060742.1628959-1-contact@xchglabs.com/
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
KVM generic changes for 7.0 - Remove a subtle pseudo-overlay of kvm_stats_desc, which, aside from being unnecessary and confusing, triggered compiler warnings due to -Wflex-array-member-not-at-end. - Document that vcpu->mutex is take outside of kvm->slots_lock and kvm->slots_arch_lock, which is intentional and desirable despite being rather unintuitive.
KVM_CAP_SYNC_MMU is provided by KVM's MMU notifiers, which are now always available. Move the definition from individual architectures to common code. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
All architectures now use MMU notifier for KVM page table management. Remove the Kconfig symbol and the code that is used when it is disabled. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook <kees@kernel.org>
KVM mediated PMU support for 6.20 Add support for mediated PMUs, where KVM gives the guest full ownership of PMU hardware (contexted switched around the fastpath run loop) and allows direct access to data MSRs and PMCs (restricted by the vPMU model), but intercepts access to control registers, e.g. to enforce event filtering and to prevent the guest from profiling sensitive host state. To keep overall complexity reasonable, mediated PMU usage is all or nothing for a given instance of KVM (controlled via module param). The Mediated PMU is disabled default, partly to maintain backwards compatilibity for existing setup, partly because there are tradeoffs when running with a mediated PMU that may be non-starters for some use cases, e.g. the host loses the ability to profile guests with mediated PMUs, the fastpath run loop is also a blind spot, entry/exit transitions are more expensive, etc. Versus the emulated PMU, where KVM is "just another perf user", the mediated PMU delivers more accurate profiling and monitoring (no risk of contention and thus dropped events), with significantly less overhead (fewer exits and faster emulation/programming of event selectors) E.g. when running Specint-2017 on a single-socket Sapphire Rapids with 56 cores and no-SMT, and using perf from within the guest: Perf command: a. basic-sampling: perf record -F 1000 -e 6-instructions -a --overwrite b. multiplex-sampling: perf record -F 1000 -e 10-instructions -a --overwrite Guest performance overhead: --------------------------------------------------------------------------- | Test case | emulated vPMU | all passthrough | passthrough with | | | | | event filters | --------------------------------------------------------------------------- | basic-sampling | 33.62% | 4.24% | 6.21% | --------------------------------------------------------------------------- | multiplex-sampling | 79.32% | 7.34% | 10.45% | ---------------------------------------------------------------------------
KVM x86 APIC-ish changes for 6.20 - Fix a benign bug where KVM could use the wrong memslots (ignored SMM) when creating a vCPU-specific mapping of guest memory. - Clean up KVM's handling of marking mapped vCPU pages dirty. - Drop a pile of *ancient* sanity checks hidden behind in KVM's unused ASSERT() macro, most of which could be trivially triggered by the guest and/or user, and all of which were useless. - Fold "struct dest_map" into its sole user, "struct rtc_status", to make it more obvious what the weird parameter is used for, and to allow burying the RTC shenanigans behind CONFIG_KVM_IOAPIC=y. - Bury all of ioapic.h and KVM_IRQCHIP_KERNEL behind CONFIG_KVM_IOAPIC=y. - Add a regression test for recent APICv update fixes. - Rework KVM's handling of VMCS updates while L2 is active to temporarily switch to vmcs01 instead of deferring the update until the next nested VM-Exit. The deferred updates approach directly contributed to several bugs, was proving to be a maintenance burden due to the difficulty in auditing the correctness of deferred updates, and was polluting "struct nested_vmx" with a growing pile of booleans. - Handle "hardware APIC ISR", a.k.a. SVI, updates in kvm_apic_update_apicv() to consolidate the updates, and to co-locate SVI updates with the updates for KVM's own cache of ISR information. - Drop a dead function declaration.
KVM guest_memfd changes for 6.20 - Remove kvm_gmem_populate()'s preparation tracking and half-baked hugepage handling, and instead rely on SNP (the only user of the tracking) to do its own tracking via the RMP. - Retroactively document and enforce (for SNP) that KVM_SEV_SNP_LAUNCH_UPDATE and KVM_TDX_INIT_MEM_REGION require the source page to be 4KiB aligned, to avoid non-trivial complexity for a non-existent usecase (and because in-place conversion simply can't support unaligned sources). - When populating guest_memfd memory, GUP the source page in common code and pass the refcounted page to the vendor callback, instead of letting vendor code do the heavy lifting. Doing so avoids a looming deadlock bug with in-place due an AB-BA conflict betwee mmap_lock and guest_memfd's filemap invalidate lock.
Currently the post-populate callbacks handle copying source pages into private GPA ranges backed by guest_memfd, where kvm_gmem_populate() acquires the filemap invalidate lock, then calls a post-populate callback which may issue a get_user_pages() on the source pages prior to copying them into the private GPA (e.g. TDX). This will not be compatible with in-place conversion, where the userspace page fault path will attempt to acquire the filemap invalidate lock while holding the mm->mmap_lock, leading to a potential ABBA deadlock. Address this by hoisting the GUP above the filemap invalidate lock so that these page faults path can be taken early, prior to acquiring the filemap invalidate lock. It's not currently clear whether this issue is reachable with the current implementation of guest_memfd, which doesn't support in-place conversion, however it does provide a consistent mechanism to provide stable source/target PFNs to callbacks rather than punting to vendor-specific code, which allows for more commonality across architectures, which may be worthwhile even without in-place conversion. As part of this change, also begin enforcing that the 'src' argument to kvm_gmem_populate() must be page-aligned, as this greatly reduces the complexity around how the post-populate callbacks are implemented, and since no current in-tree users support using a non-page-aligned 'src' argument. Suggested-by: Sean Christopherson <seanjc@google.com> Co-developed-by: Sean Christopherson <seanjc@google.com> Co-developed-by: Vishal Annapurve <vannapurve@google.com> Signed-off-by: Vishal Annapurve <vannapurve@google.com> Tested-by: Vishal Annapurve <vannapurve@google.com> Tested-by: Kai Huang <kai.huang@intel.com> Signed-off-by: Michael Roth <michael.roth@amd.com> Tested-by: Yan Zhao <yan.y.zhao@intel.com> Reviewed-by: Yan Zhao <yan.y.zhao@intel.com> Link: https://patch.msgid.link/20260108214622.1084057-7-michael.roth@amd.com [sean: avoid local "p" variable] Signed-off-by: Sean Christopherson <seanjc@google.com>