Dimanche 18 octobre 2026

Linux

In the Linux kernel, the following vulnerability has been resolved: net: stmmac: fix rx Scatter-Gather support When a received frame is larger than dma_buf_sz, the DMA scatters it across multiple RX descriptors (rx Scatter-Gather). The secondary RX buffer (sec_page) was only allocated and programmed when split-header (SPH) was active, so for regular frames buffer2 was neither allocated nor backed by a valid mapping. As soon as an incoming frame overflowed buffer1, the DMA wrote the overflow into the unmapped secondary-buffer address, triggering an SMMU translation fault on IOMMU-based platforms: arm-smmu 15000000.iommu: Unhandled context fault: fsr=0x402, iova=0x00000000, fsynr=0x7f0011, cbfrsynra=0x1c90, cb=11 arm-smmu 15000000.iommu: FSR = 00000402 [Format=2 TF], SID=0x1c90 arm-smmu 15000000.iommu: FSYNR0 = 007f0011 [S1CBNDX=127 WNR PLVL=1] Enable scatter-gather for non-SPH frames on cores that can program an independent secondary RX buffer (GMAC4/XGMAC): allocate and mark buffer2 as valid in stmmac_init_rx_buffers() and stmmac_rx_refill(), and account for it in the buffer length computation. Legacy cores have no set_sec_addr op, so they keep buffer2 disabled. Since buffer2 is handed to the DMA at page offset 0, the page pool sync window is widened to cover both buffers in every mode: offset is set to 0 and max_len to dma_buf_sz + stmmac_rx_offset(). The FCS can straddle the buffer1/buffer2 boundary and a descriptor boundary, so it is now stripped from the tail of the assembled frame with pskb_trim() instead of from a single buffer, avoiding an unsigned underflow for frames that overflow a buffer by 1..3 bytes. For single-buffer frames the XDP program must not see the FCS, so it is removed from the XDP buffer before the program runs. Native XDP currently only supports single-buffer (linear) frames. An oversized frame accepted by the MAC (jumbo enabled) is received via buffer2; the XDP program only sees buffer1, so on a TX/REDIRECT verdict the frame is forwarded truncated. XDP multi-buffer support to handle this case is planned as a follow-up. AF_XDP zero-copy RX is not covered by this change: a ZC queue still programs buffer2 at DMA address 0 (and XGMAC has no buffer2-valid bit), so an oversized frame overflowing buffer1 can still trigger the same SMMU translation fault. Handling is planned as a follow-up.

Linux

In the Linux kernel, the following vulnerability has been resolved: x86/mm: Don't apply va_align to hugetlb mappings on AMD F15h get_align_mask() returns huge_page_mask_align() for hugetlbfs, but get_align_bits() adds va_align.bits regardless, so vm_unmapped_area() returns an address off the huge page boundary and __unmap_hugepage_range() hits BUG_ON(start & ~huge_page_mask(h)) at teardown. This can be triggered on Carrizo and FX-8370E, both hstates. Pass the file to get_align_bits() and skip the randomisation for hugetlbfs. [ bp: Massage commit message. ]

Linux

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Do cache maintenance on the source VM *before* clearing SEV state Explicitly flush caches after intra-host migration before clearing "SEV active" on the source VM, as doing cache maintenance afterwards creates a tiny window where memory reclaim could return memory to the host without performing a cache flush, e.g. as pointed out by Sashiko: CPU1 in sev_migrate_from(): src->active = false; CPU2 running concurrent unmap: Since active is false, the automatic cache flush in sev_guest_memory_reclaimed is skipped. The host frees and reallocates the page. CPU1 in sev_migrate_from(): sev_writeback_caches(src_kvm); Executes a hardware cache flush (wbnoinvd), which writes the guest's old dirty ciphertext over the new page owner's data.

Linux

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: vgic: Take a refcount on IRQs referenced by last_lr_irq Referencing the last interrupt inserted in an LR is rather fragile, as this interrupt can vanish if a concurrently unmapped LPI. Solve this by bumping up the refcount on the interrupt when populating last_lr_irq, and drop it at vgic_prune_ap_list() time, when LPIs are being reclaimed.

Linux

In the Linux kernel, the following vulnerability has been resolved: smb: client: drain and invalidate before server-side copy/clone cifs_file_copychunk_range() and the clone (FICLONE) path of cifs_remap_file_range() do not serialise the destination page cache against the server-side copy the way the other server-side range operations (smb3_zero_range(), smb3_punch_hole(), smb3_collapse_range() and smb3_insert_range()) do. cifs_file_copychunk_range() invalidates the destination range with filemap_invalidate_inode(), which takes and drops the mapping's invalidate_lock internally, so the lock is no longer held when the copychunk ioctl is issued. It also never drains in-flight netfs I/O on the target. The clone path never takes the invalidate_lock at all (only i_rwsem), uses a bare truncate_inode_pages_range() and likewise does not drain outstanding I/O. As a result an asynchronous destination writeback can complete after the server-side copy/clone has run and reinstate stale data over the region just written by the server, corrupting the file. This is the same class of corruption as commit d7d2adcd022b ("smb/client: flush dirty data before punching a hole") and has been seen randomly in generic/363 against Windows Server. Fix both paths to follow the established ordering: hold the target mapping's invalidate_lock across the flush and invalidation of the destination and the server ioctl, and call netfs_wait_for_outstanding_io() on the target to drain in-flight writes before the ioctl is issued. Only the target inode's invalidate_lock is required, as the source is merely flushed and not invalidated; i_rwsem (already held via lock_two_nondirectories()) is acquired before the invalidate_lock, matching the VFS lock ordering. Since filemap_invalidate_inode() takes that same lock internally, replace it with its own unmap/flush/invalidate steps instead of calling it, and return early on a zero-length copy to avoid a range underflow.

Linux

In the Linux kernel, the following vulnerability has been resolved: net: spacemit: clear TX descriptor on fragment mapping failure emac_tx_mem_map() writes TX_DESC_0_OWN into the ring descriptor for every slot beyond old_head as soon as that slot's memset()'d local copy is committed with "*tx_desc_addr = tx_desc", i.e. before the buffers for that slot have necessarily all been mapped successfully. If emac_tx_map_frag() then fails on a later fragment, the err_free_skb path calls emac_free_tx_buf() to unmap and drop the skb, but leaves the already-written descriptor memory untouched, and tx_ring->head is never advanced past old_head (the "tx_ring->head = head" store is skipped by the goto). So a slot between old_head and the rolled-back head can be left with TX_DESC_0_OWN set and buffer_addr_{1,2} pointing at DMA mappings that emac_free_tx_buf() just tore down, while software considers that slot free again. The next successful emac_tx_mem_map() call only rebuilds old_head itself; if the DMA engine auto-advances into the following descriptor once it finishes old_head's packet, it will fetch that stale, already-unmapped address. emac_tx_clean_desc() already treats emac_free_tx_buf() and clearing the descriptor as a pair when reclaiming completed descriptors; do the same in the mapping failure path.

Linux

In the Linux kernel, the following vulnerability has been resolved: bpf, sockmap: Reject max_entries > INT_MAX in sock_map_alloc sock_map_alloc() only rejects max_entries == 0 and otherwise allows any u32 value. sock_map_free() then walks the sks[] array with a signed int iterator: int i; for (i = 0; i < stab->map.max_entries; i++) struct sock **psk = &stab->sks[i]; When a SOCKMAP is created with max_entries = 0xffffffff (UINT_MAX), the allocation of 32 GiB can succeed on large-memory hosts. During free the counter reaches 0x80000000, wraps to INT_MIN, is sign-extended by movslq and turned into a ~16 GiB negative offset from stab->sks, pointing far below the allocation. The faulting access is an xchg() write in sock_map_free(). Without KASAN, the same out-of-bounds write can fault on an unmapped vmalloc page or corrupt an unrelated allocation if that vmalloc address is populated. On a KASAN kernel with CONFIG_KASAN_VMALLOC=y, the shadow check for that address hits an unmapped shadow page and oopses first: BUG: unable to handle page fault for address: fffff521b59c5a00 RIP: 0010:kasan_check_range+0x107/0x190 Call Trace: sock_map_free+0x93/0x190 map_create+0x68d/0xb30 __sys_bpf+0x21e/0x2e70 Vmcore confirmed stab->map.max_entries == 0xffffffff, stab->sks == 0xffffc911ace2d000, and the faulting address sks + (s64)INT_MIN * 8 exactly at 0xffffc90dace2d000. The same buggy path is reached on the normal close()/bpf_map_free_deferred() path whenever such a map is destroyed. sock_map_alloc() used to bound its allocation size through bpf_map_charge_init(), but the bound was dropped when rlimit-based memory accounting was removed. Reject max_entries > INT_MAX at creation time so the signed iterator in sock_map_free() never sees a value that would overflow. Triggered by syzkaller and reproduced on both a 6.6-based KASAN kernel and the upstream v7.3-rc2 kernel.

Linux

In the Linux kernel, the following vulnerability has been resolved: rds: ib: Clear the sg list when mapping an MR fails rds_ib_map_frmr() stores the caller's scatterlist in the MR before DMA mapping and registration can fail. On failure, __rds_rdma_map() unpins the pages and frees the scatterlist, but rds_ib_free_frmr() can still return the MR to the pool with the stale pointer set. This leaves the pool with a dangling scatterlist and can lead to local privilege escalation. KASAN detects the resulting use-after-free when the MR is later torn down: BUG: KASAN: slab-use-after-free in __rds_ib_teardown_mr Read of size 8 Call Trace: __rds_ib_teardown_mr rds_ib_unreg_frmr rds_ib_flush_mr_pool rds_ib_flush_mrs rds_free_mr rds_setsockopt Store the scatterlist in the MR only after DMA mapping succeeds. If DMA mapping fails, return directly while the MR fields remain clear; the caller keeps ownership of the scatterlist and its pinned pages. If a later registration step fails, unmap the scatterlist and clear the MR fields before returning.

Linux

In the Linux kernel, the following vulnerability has been resolved: drm/imagination: Propagate map failures correctly from pvr_mmu_map_sgl() Map failure from pvr_mmu_map_sgl() interface was not returned correctly to pvr_mmu_map() interface. This resulted in pvr_mmu_map() interface to continue instead of returning an error to caller. Fix it by returning a proper error code from pvr_mmu_map_sgl() interface. Call stack for crash: [ 1179.286237] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 [ 1179.295067] Mem abort info: [ 1179.297877] ESR = 0x0000000096000004 [ 1179.301656] EC = 0x25: DABT (current EL), IL = 32 bits [ 1179.306987] SET = 0, FnV = 0 [ 1179.310048] EA = 0, S1PTW = 0 [ 1179.313198] FSC = 0x04: level 0 translation fault [ 1179.318096] Data abort info: [ 1179.320993] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000 [ 1179.326483] CM = 0, WnR = 0, TnD = 0, TagAccess = 0 [ 1179.331546] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 [ 1179.336895] user pgtable: 4k pages, 48-bit VAs, pgdp=000000009822a000 [ 1179.343402] [0000000000000008] pgd=0000000000000000, p4d=0000000000000000 [ 1179.350243] Internal error: Oops: 0000000096000004 [#2] SMP [ 1179.355908] Modules linked in: powervr gpu_sched drm_shmem_helper drm_gpuvm drm_exec xhci_plat_hcd xhci_hcd dwc3 usbcore usb_common snd_soc_simple_card snd_soc_simple_card_utils dwc3_am62 at24 sa2ul sha512 libsha512 sha256 authenc sch_fq_codel fuse dm_mod ipv6 [ 1179.378992] CPU: 1 UID: 1000 PID: 680 Comm: deqp-vk Tainted: G D 6.17.0 #1 PREEMPT [ 1179.388120] Tainted: [D]=DIE [ 1179.390994] Hardware name: Texas Instruments AM625 SK (DT) [ 1179.396467] pstate: 00000005 (nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 1179.403415] pc : pvr_mmu_op_context_unmap_curr_page+0x6c/0x134 [powervr] [ 1179.410140] lr : pvr_mmu_op_context_unmap_curr_page+0x58/0x134 [powervr] [ 1179.416848] sp : ffff8000839ab8c0 [ 1179.420153] x29: ffff8000839ab8c0 x28: 0000000000000001 x27: 000000008f386000 [ 1179.427283] x26: ffff000016d1df98 x25: 0000000000247000 x24: 00000000000001e6 [ 1179.434413] x23: 0000000000000002 x22: 000000000000ffff x21: 0000000000000247 [ 1179.441540] x20: 0000000000000245 x19: ffff000016d1df60 x18: 0000000000000002 [ 1179.448668] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000001 [ 1179.455793] x14: 0000000000060810 x13: ffff80007fffffff x12: ffff000004190480 [ 1179.462921] x11: ffff8000853f7000 x10: ffff8000811ae000 x9 : ffff0000041900b8 [ 1179.470051] x8 : 0000000000000000 x7 : 00000000990c4001 x6 : 0000000000000007 [ 1179.477177] x5 : ffff000016d1df60 x4 : 0000000000000000 x3 : ffff00000a7d8000 [ 1179.484306] x2 : 00000000000001ff x1 : 0000000000000000 x0 : 0000000000000000 [ 1179.491433] Call trace: [ 1179.493872] pvr_mmu_op_context_unmap_curr_page+0x6c/0x134 [powervr] (P) [ 1179.500582] pvr_mmu_map+0x31c/0x388 [powervr] [ 1179.505027] pvr_vm_gpuva_map+0x40/0x88 [powervr] [ 1179.509732] __drm_gpuvm_sm_map+0x250/0x44c [drm_gpuvm] [ 1179.514952] drm_gpuvm_sm_map+0x48/0x5c [drm_gpuvm] [ 1179.519822] pvr_vm_bind_op_exec+0x64/0x70 [powervr] [ 1179.524785] pvr_vm_map+0x1f8/0x2a8 [powervr] [ 1179.529142] pvr_ioctl_vm_map+0x12c/0x188 [powervr] [ 1179.534018] drm_ioctl_kernel+0xb8/0x128 [ 1179.537941] drm_ioctl+0x21c/0x4ec [ 1179.541337] __arm64_sys_ioctl+0xac/0x108 [ 1179.545344] invoke_syscall+0x44/0x100 [ 1179.549091] el0_svc_common.constprop.0+0x40/0xe0 [ 1179.553790] do_el0_svc+0x1c/0x28 [ 1179.557106] el0_svc+0x34/0xf0 [ 1179.560159] el0t_64_sync_handler+0xd0/0xe4 [ 1179.564334] el0t_64_sync+0x198/0x19c [ 1179.567996] Code: 54000300 35000360 f9402261 79409a62 (f9400421) [ 1179.574081] ---[ end trace 0000000000000000 ]---

Linux

In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: fix use-after-free and multi-container gap in kfd_dev_mapping kfd_dev_mapping caches the address_space of the first /dev/kfd opener so that the GPU reset path can call unmap_mapping_range() to zap all userspace mappings of doorbell and MMIO ranges. This design has two bugs that both manifest under SRIOV with multiple containers: 1. Use-after-free / rwsem deadlock. The cached pointer refers to an inode owned by the first opener's container. When that container exits and its inode is released, kfd_dev_mapping becomes a dangling pointer. A subsequent GPU reset dereferences it inside unmap_mapping_range(), which takes i_mmap_rwsem on the freed inode, causing a hard hang observable as an uninterruptible rwsem wait. 2. Multi-container gap. Only the first opener's address_space is cached; VMAs created by later openers live in a different address_space and are never reached by unmap_mapping_range(). After a GPU reset those stale mappings keep doorbell and MMIO pages accessible to guest userspace with no GPU behind them, risking PCIe transaction timeouts and NMI panics. Fix both bugs with the same approach used by DRM core (drm_drv.c): create a private pseudo-filesystem at module init time and allocate one anonymous inode from it. In kfd_open() redirect every opener's file->f_mapping to that inode's address_space. The inode is module-owned, lives exactly as long as the amdgpu module, and collects VMAs from all openers in one address_space. A single unmap_mapping_range() call in the reset path then correctly reaches every container's mappings with no dangling pointer risk. The hang manifests as an NMI backtrace on the GPU reset workqueue stuck spinning in rwsem_down_read_slowpath() with a corrupted i_mmap_rwsem: Workqueue: amdgpu-reset-dev xgpu_ai_mailbox_flr_work [amdgpu] Call Trace: <TASK> kvm_wait+0x1f/0x40 __pv_queued_spin_lock_slowpath+0x31d/0x3a0 _raw_spin_lock_irq+0x51/0x80 rwsem_down_read_slowpath+0xb3/0x550 down_read+0x48/0xd0 unmap_mapping_range+0x71/0x140 kfd_dev_unmap_mapping_range+0x5b/0x140 [amdgpu] amdgpu_amdkfd_clear_kfd_mapping+0xd8/0x190 [amdgpu] amdgpu_device_gpu_recover+0x232/0x450 [amdgpu] xgpu_ai_mailbox_flr_work+0xb5/0xc0 [amdgpu] process_one_work+0x18e/0x3e0 worker_thread+0x2e3/0x420 kthread+0x10a/0x230 (cherry picked from commit 1128b4a52de1572e87431de837fd9850cb99542c)

Linux

In the Linux kernel, the following vulnerability has been resolved: drm/nouveau/uvmm: fix UAF in nouveau_uvmm_sm when BO is in TTM_PL_SYSTEM nouveau_uvmm_sm() calls op_map(), which passes bo->resource through nouveau_mem() to nouveau_uvma_map(). nouveau_uvmm_vmm_map() then reads mem->mem.type. But this is only valid when bo->resource is backed by struct nouveau_mem, as is the case for VRAM and TT resources. If the BO is left in TTM_PL_SYSTEM, bo->resource is only a struct ttm_resource. Treating it as struct nouveau_mem makes the mem->mem.type read past the end of the resource, causing a KASAN: slab-use-after-free Read in nouveau_uvmm_sm report: BUG: KASAN: slab-use-after-free in nouveau_uvmm_vmm_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:152 [inline] BUG: KASAN: slab-use-after-free in nouveau_uvma_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:199 [inline] BUG: KASAN: slab-use-after-free in op_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:849 [inline] BUG: KASAN: slab-use-after-free in nouveau_uvmm_sm.constprop.0+0x6ab/0x900 drivers/gpu/drm/nouveau/nouveau_uvmm.c:903 Read of size 1 at addr ffff888127d3e3a0 by task kworker/0:1/11 CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 7.2.0 #5 PREEMPT(lazy) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: nouveau_sched_wq_2224 drm_sched_run_job_work Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x95/0xe0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xcb/0x5a0 mm/kasan/report.c:482 kasan_report+0xca/0x100 mm/kasan/report.c:595 nouveau_uvmm_vmm_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:152 [inline] nouveau_uvma_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:199 [inline] op_map drivers/gpu/drm/nouveau/nouveau_uvmm.c:849 [inline] nouveau_uvmm_sm.constprop.0+0x6ab/0x900 drivers/gpu/drm/nouveau/nouveau_uvmm.c:903 nouveau_uvmm_sm_unmap drivers/gpu/drm/nouveau/nouveau_uvmm.c:932 [inline] nouveau_uvmm_bind_job_run+0xd6/0x250 drivers/gpu/drm/nouveau/nouveau_uvmm.c:1532 nouveau_job_run drivers/gpu/drm/nouveau/nouveau_sched.c:350 [inline] nouveau_sched_run_job+0x62/0xd0 drivers/gpu/drm/nouveau/nouveau_sched.c:364 drm_sched_run_job_work+0x356/0xa10 drivers/gpu/drm/scheduler/sched_main.c:1061 process_one_work+0x8a5/0x1900 kernel/workqueue.c:3322 process_scheduled_works kernel/workqueue.c:3405 [inline] worker_thread+0x5dd/0xd80 kernel/workqueue.c:3486 kthread+0x31d/0x420 kernel/kthread.c:436 ret_from_fork+0x662/0x940 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> Allocated by task 2224 on cpu 0 at 66.550027s: kasan_save_stack+0x24/0x50 mm/kasan/common.c:57 kasan_save_track+0x17/0x60 mm/kasan/common.c:78 poison_kmalloc_redzone mm/kasan/common.c:398 [inline] __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415 kasan_kmalloc include/linux/kasan.h:263 [inline] __do_kmalloc_node mm/slub.c:5334 [inline] __kmalloc_noprof+0x304/0x7c0 mm/slub.c:5359 _kmalloc_noprof include/linux/slab.h:992 [inline] dma_resv_list_alloc+0x27/0x90 drivers/dma-buf/dma-resv.c:106 dma_resv_reserve_fences+0x60e/0xa30 drivers/dma-buf/dma-resv.c:205 ttm_bo_alloc_resource+0x12c/0xbd0 drivers/gpu/drm/ttm/ttm_bo.c:721 ttm_bo_validate+0x1bc/0x4a0 drivers/gpu/drm/ttm/ttm_bo.c:856 ttm_bo_init_reserved+0x2c3/0x570 drivers/gpu/drm/ttm/ttm_bo.c:970 nouveau_bo_init+0x159/0x2c0 drivers/gpu/drm/nouveau/nouveau_bo.c:359 nouveau_gem_new+0x234/0x5f0 drivers/gpu/drm/nouveau/nouveau_gem.c:272 nouveau_gem_ioctl_new+0x1eb/0x420 drivers/gpu/drm/nouveau/nouveau_gem.c:352 drm_ioctl_kernel+0x192/0x350 drivers/gpu/drm/drm_ioctl.c:817 drm_ioctl+0x4f8/0xb40 drivers/gpu/drm/drm_ioctl.c:914 nouveau_drm_ioctl+0xea/0x2c0 drivers/gpu/drm/nouveau/nouveau_drm.c:1338 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x180/0x1d0 fs/ioctl.c:583 do_syscall_x64 ar ---truncated---

Linux

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Fix spurious warning for benign stage 2 teardown race kvmtool was used to establish an L1 guest with 8 CPUs and 8 GiB of RAM, an L2 guest with 4 CPUs and 4 GiB of RAM and an L3 guest with 2 CPUs and 2 GiB of RAM, all of which was then exited. Under memory pressure in the L0 host warnings were observed due to migration triggered by compaction: WARNING: arch/arm64/kvm/mmu.c:336 at __unmap_stage2_range+0x64/0x80, CPU#5: kcompactd0/66 Which was, in turn, triggered by an MMU notifier for the host invalidation: mmu_notifier_invalidate_range_start() -> ... -> kvm_mmu_notifier_invalidate_range_start() -> kvm_mmu_unmap_gfn_range() -> kvm_unmap_gfn_range() -> kvm_nested_s2_unmap() -> kvm_stage2_unmap_range() -> __unmap_stage2_range() -> stage2_apply_range() <- -EINVAL, triggering a WARN_ON() Racing with L0's teardown of stage 2 page tables: exit_mm() -> mmput() -> __mmput() -> exit_mmap() -> mmu_notifier_release() -> ... -> kvm_mmu_notifier_release() -> kvm_flush_shadow_all() -> kvm_arch_flush_shadow_all() -> kvm_free_stage2_pgd() -> [ acquire kvm->mmu_lock for write ] -> mmu->pgt = NULL [ among other tasks ] -> [ release kvm->mmu_lock for write ] It turns out there is a benign race resulting in a spurious warning: Thread A - notify: migration | Thread B - notify: release -------------------------------|--------------------------------- < kvm->mmu_lock held > | stage2_apply_range() | get mmu->pgt, check !NULL | ... | kvm_arch_flush_shadow_all() cond_resched_rwlock_write(); | < contend, sleep kvm->mmu_lock > < drop kvm->mmu_lock > | < acquire kvm->mmu_lock> | ... | kvm_free_stage2_pgd() | mmu->pgt = NULL | < invalidate MMU > | ... | < release kvm->mmu_lock > [ scheduled ] | stage2_apply_range() | < loop to next > | get, mmu->pgt, check !NULL | is NULL, return -EINVAL | __unmap_stage2_range() | WARN_ON(-EINVAL) <--- entirely spurious - the race was handled correctly. Fix the spurious warning by updating stage2_apply_range() to no longer treat concurrent PGT teardown on lock release as an error - whether the walker is tearing down page tables or doing something else this is a legitimate reason to abort the operation without error. This keeps the warning in place for all other circumstances. In practice only __unmap_stage2_range() actually does anything with the error so this only impacts that.

Linux

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: nv: Fix null ptr deref on nested wp/unmap, teardown race Commit 7270cc9157f4 ("KVM: arm64: nv: Handle VNCR_EL2 invalidation from MMU notifiers") introduced VNCR_EL2 invalidation in both kvm_nested_s2_unmap() and kvm_nested_s2_wp(). However at the point of this being performed concurrent stage 2 teardown of a nested guest can cause kvm->arch.mmu.pgt to be set to NULL. This happens in kvm_flush_shadow_all() -> kvm_arch_flush_shadow_all() -> kvm_free_stage2_pgd() and is performed under the kvm->mmu_lock. Commit ec14c272408a ("KVM: arm64: nv: Unmap/flush shadow stage 2 page tables") introduced the teardown of the entire nested MMU range, which then invokes stage2_apply_range() with resched=true: mmu_notifier_invalidate_range_start() -> ... -> kvm_mmu_notifier_invalidate_range_start() -> kvm_mmu_unmap_gfn_range() -> kvm_unmap_gfn_range() -> kvm_nested_s2_unmap() -> kvm_stage2_unmap_range() -> __unmap_stage2_range() -> stage2_apply_range() This means that stage2_apply_range() can drop the kvm->mmu_lock and thus concurrent progress can be made in lockstep with kvm_arch_flush_shadow_all(). If kvm_arch_flush_shadow_all() advances ahead of stage2_apply_range() and completes its operation it guarantees a NULL pointer deref. Since kvm_free_stage2_pgd() is performed under the kvm->mmu_lock this will either be observed NULL or not and serialised against kvm_free_stage2_pgd(). Resolve the issue by abstracting the invalidation to a new function, kvm_invalidate_vncr_ipa_all(), and check that the pgt is non-NULL before dereferencing it.