86931ff720
Disallow memslots and MMIO SPTEs whose gpa range would exceed the host's
MAXPHYADDR, i.e. don't create SPTEs for gfns that exceed host.MAXPHYADDR.
The TDP MMU bounds its zapping based on host.MAXPHYADDR, and so if the
guest, possibly with help from userspace, manages to coerce KVM into
creating a SPTE for an "impossible" gfn, KVM will leak the associated
shadow pages (page tables):
WARNING: CPU: 10 PID: 1122 at arch/x86/kvm/mmu/tdp_mmu.c:57
kvm_mmu_uninit_tdp_mmu+0x4b/0x60 [kvm]
Modules linked in: kvm_intel kvm irqbypass
CPU: 10 PID: 1122 Comm: set_memory_regi Tainted: G W 5.18.0-rc1+ #293
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x4b/0x60 [kvm]
Call Trace:
<TASK>
kvm_arch_destroy_vm+0x130/0x1b0 [kvm]
kvm_destroy_vm+0x162/0x2d0 [kvm]
kvm_vm_release+0x1d/0x30 [kvm]
__fput+0x82/0x240
task_work_run+0x5b/0x90
exit_to_user_mode_prepare+0xd2/0xe0
syscall_exit_to_user_mode+0x1d/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
On bare metal, encountering an impossible gpa in the page fault path is
well and truly impossible, barring CPU bugs, as the CPU will signal #PF
during the gva=>gpa translation (or a similar failure when stuffing a
physical address into e.g. the VMCS/VMCB). But if KVM is running as a VM
itself, the MAXPHYADDR enumerated to KVM may not be the actual MAXPHYADDR
of the underlying hardware, in which case the hardware will not fault on
the illegal-from-KVM's-perspective gpa.
Alternatively, KVM could continue allowing the dodgy behavior and simply
zap the max possible range. But, for hosts with MAXPHYADDR < 52, that's
a (minor) waste of cycles, and more importantly, KVM can't reasonably
support impossible memslots when running on bare metal (or with an
accurate MAXPHYADDR as a VM). Note, limiting the overhead by checking if
KVM is running as a guest is not a safe option as the host isn't required
to announce itself to the guest in any way, e.g. doesn't need to set the
HYPERVISOR CPUID bit.
A second alternative to disallowing the memslot behavior would be to
disallow creating a VM with guest.MAXPHYADDR > host.MAXPHYADDR. That
restriction is undesirable as there are legitimate use cases for doing
so, e.g. using the highest host.MAXPHYADDR out of a pool of heterogeneous
systems so that VMs can be migrated between hosts with different
MAXPHYADDRs without running afoul of the allow_smaller_maxphyaddr mess.
Note that any guest.MAXPHYADDR is valid with shadow paging, and it is
even useful in order to test KVM with MAXPHYADDR=52 (i.e. without
any reserved physical address bits).
The now common kvm_mmu_max_gfn() is inclusive instead of exclusive.
The memslot and TDP MMU code want an exclusive value, but the name
implies the returned value is inclusive, and the MMIO path needs an
inclusive check.
Fixes:
|
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.