Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! 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User-controlled indices are used to access AIA CSR registers.
Sanitize them with array_index_nospec() to prevent speculative
out-of-bounds access.
Similar to x86 commit 8c86405f606c ("KVM: x86: Protect
ioapic_read_indirect() from Spectre-v1/L1TF attacks") and arm64
commit 41b87599c743 ("KVM: arm/arm64: vgic: fix possible spectre-v1
in vgic_get_irq()").
Reviewed-by: Radim Krčmář <radim.krcmar@oss.qualcomm.com>
Signed-off-by: Lukas Gerlach <lukas.gerlach@cispa.de>
Link: https://lore.kernel.org/r/20260303-kvm-riscv-spectre-v1-v2-2-192caab8e0dc@cispa.de
Signed-off-by: Anup Patel <anup@brainfault.org>
User-controlled register indices from the ONE_REG ioctl are used to
index into arrays of register values. Sanitize them with
array_index_nospec() to prevent speculative out-of-bounds access.
Reviewed-by: Radim Krčmář <radim.krcmar@oss.qualcomm.com>
Signed-off-by: Lukas Gerlach <lukas.gerlach@cispa.de>
Link: https://lore.kernel.org/r/20260303-kvm-riscv-spectre-v1-v2-1-192caab8e0dc@cispa.de
Signed-off-by: Anup Patel <anup@brainfault.org>
When dirty logging is enabled, guest stage mappings are forced to
PAGE_SIZE granularity. Changing the mapping page size at this point
is incorrect.
Fixes: ed7ae7a34bea ("RISC-V: KVM: Transparent huge page support")
Signed-off-by: Wang Yechao <wang.yechao255@zte.com.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260226191231140_X1Juus7s2kgVlc0ZyW_K@zte.com.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
The KVM_DEV_RISCV_AIA_GRP_APLIC branch of aia_has_attr() was identified
to have a race condition with concurrent KVM_SET_DEVICE_ATTR ioctls,
leading to a use-after-free bug.
Upon analyzing the code, it was discovered that the
KVM_DEV_RISCV_AIA_GRP_IMSIC branch of aia_has_attr() suffers from the same
lack of synchronization. It invokes kvm_riscv_aia_imsic_has_attr() without
holding dev->kvm->lock.
While aia_has_attr() is running, a concurrent aia_set_attr() could call
aia_init() under the dev->kvm->lock. If aia_init() fails, it may trigger
kvm_riscv_vcpu_aia_imsic_cleanup(), which frees imsic_state. Without proper
locking, kvm_riscv_aia_imsic_has_attr() could attempt to access imsic_state
while it is being deallocated.
Although this specific path has not yet been reported by a fuzzer, it
is logically identical to the APLIC issue. Fix this by acquiring the
dev->kvm->lock before calling kvm_riscv_aia_imsic_has_attr(), ensuring
consistency with the locking pattern used for other AIA attribute groups.
Fixes: 5463091a51cf ("RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260304080804.2281721-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
Fuzzer reports a KASAN use-after-free bug triggered by a race
between KVM_HAS_DEVICE_ATTR and KVM_SET_DEVICE_ATTR ioctls on
the AIA device. The root cause is that aia_has_attr() invokes
kvm_riscv_aia_aplic_has_attr() without holding dev->kvm->lock, while
a concurrent aia_set_attr() may call aia_init() under that lock. When
aia_init() fails after kvm_riscv_aia_aplic_init() has succeeded, it
calls kvm_riscv_aia_aplic_cleanup() in its fail_cleanup_imsics path,
which frees both aplic_state and aplic_state->irqs. The concurrent
has_attr path can then dereference the freed aplic->irqs in
aplic_read_pending():
irqd = &aplic->irqs[irq]; /* UAF here */
KASAN report:
BUG: KASAN: slab-use-after-free in aplic_read_pending
arch/riscv/kvm/aia_aplic.c:119 [inline]
BUG: KASAN: slab-use-after-free in aplic_read_pending_word
arch/riscv/kvm/aia_aplic.c:351 [inline]
BUG: KASAN: slab-use-after-free in aplic_mmio_read_offset
arch/riscv/kvm/aia_aplic.c:406
Read of size 8 at addr ff600000ba965d58 by task 9498
Call Trace:
aplic_read_pending arch/riscv/kvm/aia_aplic.c:119 [inline]
aplic_read_pending_word arch/riscv/kvm/aia_aplic.c:351 [inline]
aplic_mmio_read_offset arch/riscv/kvm/aia_aplic.c:406
kvm_riscv_aia_aplic_has_attr arch/riscv/kvm/aia_aplic.c:566
aia_has_attr arch/riscv/kvm/aia_device.c:469
allocated by task 9473:
kvm_riscv_aia_aplic_init arch/riscv/kvm/aia_aplic.c:583
aia_init arch/riscv/kvm/aia_device.c:248 [inline]
aia_set_attr arch/riscv/kvm/aia_device.c:334
freed by task 9473:
kvm_riscv_aia_aplic_cleanup arch/riscv/kvm/aia_aplic.c:644
aia_init arch/riscv/kvm/aia_device.c:292 [inline]
aia_set_attr arch/riscv/kvm/aia_device.c:334
Fix this race by acquiring dev->kvm->lock in aia_has_attr() before
calling kvm_riscv_aia_aplic_has_attr(), consistent with the locking
pattern used in aia_get_attr() and aia_set_attr().
Fixes: 289a007b98b06d ("RISC-V: KVM: Expose APLIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260302132703.1721415-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
The indexed array only has RISCV_KVM_MAX_COUNTERS elements.
The out-of-bound access could have been performed by a guest,
but it could only access another guest accessible data.
Fixes: 8f0153ecd3bf ("RISC-V: KVM: Add skeleton support for perf")
Signed-off-by: Radim Krčmář <radim.krcmar@oss.qualcomm.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260227134617.23378-1-radim.krcmar@oss.qualcomm.com
Signed-off-by: Anup Patel <anup@brainfault.org>
kvm_riscv_vcpu_aia_rmw_topei() assumes that the per-vCPU IMSIC state has
been initialized once AIA is reported as available and initialized at
the VM level. This assumption does not always hold.
Under fuzzed ioctl sequences, a guest may access the IMSIC TOPEI CSR
before the vCPU IMSIC state is set up. In this case,
vcpu->arch.aia_context.imsic_state is still NULL, and the TOPEI RMW path
dereferences it unconditionally, leading to a host kernel crash.
The crash manifests as:
Unable to handle kernel paging request at virtual address
dfffffff0000000e
...
kvm_riscv_vcpu_aia_imsic_rmw arch/riscv/kvm/aia_imsic.c:909
kvm_riscv_vcpu_aia_rmw_topei arch/riscv/kvm/aia.c:231
csr_insn arch/riscv/kvm/vcpu_insn.c:208
system_opcode_insn arch/riscv/kvm/vcpu_insn.c:281
kvm_riscv_vcpu_virtual_insn arch/riscv/kvm/vcpu_insn.c:355
kvm_riscv_vcpu_exit arch/riscv/kvm/vcpu_exit.c:230
kvm_arch_vcpu_ioctl_run arch/riscv/kvm/vcpu.c:1008
...
Fix this by explicitly checking whether the vCPU IMSIC state has been
initialized before handling TOPEI CSR accesses. If not, forward the CSR
emulation to user space.
Fixes: db8b7e97d6137 ("RISC-V: KVM: Add in-kernel virtualization of AIA IMSIC")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260226085119.643295-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
While fuzzing KVM on RISC-V, a use-after-free was observed in
kvm_riscv_gstage_get_leaf(), where ptep_get() dereferences a
freed gstage page table page during gfn unmap.
The crash manifests as:
use-after-free in ptep_get include/linux/pgtable.h:340 [inline]
use-after-free in kvm_riscv_gstage_get_leaf arch/riscv/kvm/gstage.c:89
Call Trace:
ptep_get include/linux/pgtable.h:340 [inline]
kvm_riscv_gstage_get_leaf+0x2ea/0x358 arch/riscv/kvm/gstage.c:89
kvm_riscv_gstage_unmap_range+0xf0/0x308 arch/riscv/kvm/gstage.c:265
kvm_unmap_gfn_range+0x168/0x1fc arch/riscv/kvm/mmu.c:256
kvm_mmu_unmap_gfn_range virt/kvm/kvm_main.c:724 [inline]
page last free pid 808 tgid 808 stack trace:
kvm_riscv_mmu_free_pgd+0x1b6/0x26a arch/riscv/kvm/mmu.c:457
kvm_arch_flush_shadow_all+0x1a/0x24 arch/riscv/kvm/mmu.c:134
kvm_flush_shadow_all virt/kvm/kvm_main.c:344 [inline]
The UAF is caused by gstage page table walks running concurrently with
gstage pgd teardown. In particular, kvm_unmap_gfn_range() can traverse
gstage page tables while kvm_arch_flush_shadow_all() frees the pgd,
leading to use-after-free of page table pages.
Fix the issue by serializing gstage unmap and pgd teardown with
kvm->mmu_lock. Holding mmu_lock ensures that gstage page tables
remain valid for the duration of unmap operations and prevents
concurrent frees.
This matches existing RISC-V KVM usage of mmu_lock to protect gstage
map/unmap operations, e.g. kvm_riscv_mmu_iounmap.
Fixes: dd82e35638d67f ("RISC-V: KVM: Factor-out g-stage page table management")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260202040059.1801167-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
Guests can control IRQ indices via MMIO. Sanitize them with
array_index_nospec() to prevent speculative out-of-bounds access
to the aplic->irqs[] array.
Similar to arm64 commit 41b87599c743 ("KVM: arm/arm64: vgic: fix possible
spectre-v1 in vgic_get_irq()") and x86 commit 8c86405f606c ("KVM: x86:
Protect ioapic_read_indirect() from Spectre-v1/L1TF attacks").
Fixes: 74967aa208e2 ("RISC-V: KVM: Add in-kernel emulation of AIA APLIC")
Signed-off-by: Lukas Gerlach <lukas.gerlach@cispa.de>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260116095731.24555-1-lukas.gerlach@cispa.de
Signed-off-by: Anup Patel <anup@brainfault.org>
Pull kvm fixes from Paolo Bonzini:
"Arm:
- Make sure we don't leak any S1POE state from guest to guest when
the feature is supported on the HW, but not enabled on the host
- Propagate the ID registers from the host into non-protected VMs
managed by pKVM, ensuring that the guest sees the intended feature
set
- Drop double kern_hyp_va() from unpin_host_sve_state(), which could
bite us if we were to change kern_hyp_va() to not being idempotent
- Don't leak stage-2 mappings in protected mode
- Correctly align the faulting address when dealing with single page
stage-2 mappings for PAGE_SIZE > 4kB
- Fix detection of virtualisation-capable GICv5 IRS, due to the
maintainer being obviously fat fingered... [his words, not mine]
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
Generic:
- Remove internal Kconfigs that are now set on all architectures
- Remove per-architecture code to enable KVM_CAP_SYNC_MMU, all
architectures finally enable it in Linux 7.0"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
KVM: always define KVM_CAP_SYNC_MMU
KVM: remove CONFIG_KVM_GENERIC_MMU_NOTIFIER
KVM: arm64: Deduplicate ASID retrieval code
irqchip/gic-v5: Fix inversion of IRS_IDR0.virt flag
KVM: arm64: Revert accidental drop of kvm_uninit_stage2_mmu() for non-NV VMs
KVM: arm64: Fix protected mode handling of pages larger than 4kB
KVM: arm64: vgic: Handle const qualifier from gic_kvm_info allocation type
KVM: arm64: Remove redundant kern_hyp_va() in unpin_host_sve_state()
KVM: arm64: Fix ID register initialization for non-protected pKVM guests
KVM: arm64: Optimise away S1POE handling when not supported by host
KVM: arm64: Hide S1POE from guests when not supported by the host
Pull debugobjects fix from Thomas Gleixner:
"A single fix for debugobjects.
The deferred page initialization prevents debug objects from
allocating slab pages until the initialization is complete. That
causes depletion of the pool and disabling of debugobjects.
The reason is that debugobjects uses __GFP_HIGH for allocations as it
might be invoked from arbitrary contexts. When PREEMPT_COUNT is
disabled there is no way to know whether the context is safe to set
__GFP_KSWAPD_RECLAIM.
This worked until v6.18. Since then allocations w/o a reclaim flag
cause new_slab() to end up in alloc_frozen_pages_nolock_noprof(),
which returns early when deferred page initialization has not yet
completed.
Work around that when PREEMPT_COUNT is enabled as the preempt counter
allows debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when
the context is preemtible. When PREEMPT_COUNT is disabled the context
is unknown and the reclaim bit can't be set because the caller might
hold locks which might deadlock in the allocator.
That makes debugobjects depend on PREEMPT_COUNT ||
!DEFERRED_STRUCT_PAGE_INIT, which limits the coverage slightly, but
keeps it functional for most cases"
* tag 'core-debugobjects-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
debugobject: Make it work with deferred page initialization - again
KVM/arm64 fixes for 7.0, take #1
- Make sure we don't leak any S1POE state from guest to guest when
the feature is supported on the HW, but not enabled on the host
- Propagate the ID registers from the host into non-protected VMs
managed by pKVM, ensuring that the guest sees the intended feature set
- Drop double kern_hyp_va() from unpin_host_sve_state(), which could
bite us if we were to change kern_hyp_va() to not being idempotent
- Don't leak stage-2 mappings in protected mode
- Correctly align the faulting address when dealing with single page
stage-2 mappings for PAGE_SIZE > 4kB
- Fix detection of virtualisation-capable GICv5 IRS, due to the
maintainer being obviously fat fingered...
- Remove duplication of code retrieving the ASID for the purpose of
S1 PT handling
- Fix slightly abusive const-ification in vgic_set_kvm_info()
Pull x86 fixes from Ingo Molnar:
- Fix speculative safety in fred_extint()
- Fix __WARN_printf() trap in early_fixup_exception()
- Fix clang-build boot bug for unusual alignments, triggered by
CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y
- Replace the final few __ASSEMBLY__ stragglers that snuck in lately
into non-UAPI x86 headers and use __ASSEMBLER__ consistently (again)
* tag 'x86-urgent-2026-03-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/headers: Replace __ASSEMBLY__ stragglers with __ASSEMBLER__
x86/cfi: Fix CFI rewrite for odd alignments
x86/bug: Handle __WARN_printf() trap in early_fixup_exception()
x86/fred: Correct speculative safety in fred_extint()
debugobjects uses __GFP_HIGH for allocations as it might be invoked
within locked regions. That worked perfectly fine until v6.18. It still
works correctly when deferred page initialization is disabled and works
by chance when no page allocation is required before deferred page
initialization has completed.
Since v6.18 allocations w/o a reclaim flag cause new_slab() to end up in
alloc_frozen_pages_nolock_noprof(), which returns early when deferred
page initialization has not yet completed. As the deferred page
initialization takes quite a while the debugobject pool is depleted and
debugobjects are disabled.
This can be worked around when PREEMPT_COUNT is enabled as that allows
debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when the context
is preemtible. When PREEMPT_COUNT is disabled the context is unknown and
the reclaim bit can't be set because the caller might hold locks which
might deadlock in the allocator.
In preemptible context the reclaim bit is harmless and not a performance
issue as that's usually invoked from slow path initialization context.
That makes debugobjects depend on PREEMPT_COUNT || !DEFERRED_STRUCT_PAGE_INIT.
Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://patch.msgid.link/87pl6gznti.ffs@tglx
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>
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