mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
synced 2026-10-28 12:53:14 +01:00
Sean Christopherson
b6249c1d56
When walking shadow page tables, immediately terminate the walk if the root
is a "dummy" root, i.e. a root whose top-level page table is backed by the
zero page, but otherwise doesn't exist. If memslot creation races with a
stage-2 page fault (EPT violation or #NPF) from L2, then if the stars align,
KVM will attempt to walk shadow page tables using the zero page and hit a
NULL pointer deref.
BUG: kernel NULL pointer dereference, address: 0000000000000021
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP
CPU: 30 UID: 1000 PID: 941 Comm: qemu Not tainted 7.2.0-rc2-1b731e5ded48-next-vm #1741 PREEMPTLAZY
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:__kvm_mmu_invalidate_addr+0xea/0x210 [kvm]
Call Trace:
<TASK>
kvm_mmu_invalidate_addr+0x92/0xe0 [kvm]
__kvm_inject_emulated_page_fault+0x67/0x80 [kvm]
ept_page_fault+0x160/0x850 [kvm]
kvm_mmu_do_page_fault+0x102/0x1f0 [kvm]
kvm_mmu_page_fault+0x8e/0x6b0 [kvm]
vmx_handle_exit+0x163/0x640 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0x960/0x2120 [kvm]
kvm_vcpu_ioctl+0x2c7/0x970 [kvm]
__x64_sys_ioctl+0x90/0xd0
do_syscall_64+0x67/0x5f0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7f606d0b53bb
Opportunistically harden the shadow walks against fully invalid roots, but
WARN, as all callers are expected/required to pre-check for a valid root.
Don't WARN in the dummy root case as the whole point of using a dummy root
is to provide a root that's valid enough to enter the guest, i.e. it should
Just Work for all flows except those that *need* to know about dummy roots.
Alternatively, KVM could allocate a dedicated page and associated shadow
page structure for the dummy root, which is very tempting as it such an
approach should be more resilient against unexpected behavior. But that
would be a much larger and thus riskier change than simply terminating
walks of dummy roots.
Fixes: 0e3223d8d0 ("KVM: x86/mmu: Use dummy root, backed by zero page, for !visible guest roots")
Reported-by: Gabriel Schneider <[email protected]>
Cc: [email protected]
Signed-off-by: Sean Christopherson <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
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! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst