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17a2c62fbf
Explicitly verify the MSR load/store list counts are below the advertised
limit as part of the initial consistency checks on the lists, so that code
that consumes the count doesn't need to worry about extreme edge cases.
Enforcing the limit during the initial checks fixes a flaw on 32-bit KVM
where a sufficiently high @count could lead to overflow:
arch/x86/kvm/vmx/nested.c:834 nested_vmx_check_msr_switch()
warn: potential user controlled sizeof overflow 'addr + count * 16' '0-u64max + 16-68719476720'
arch/x86/kvm/vmx/nested.c
827 static int nested_vmx_check_msr_switch(struct kvm_vcpu *vcpu,
828 u32 count, u64 addr)
829 {
830 if (count == 0)
831 return 0;
832
833 if (!kvm_vcpu_is_legal_aligned_gpa(vcpu, addr, 16) ||
--> 834 !kvm_vcpu_is_legal_gpa(vcpu, (addr + count * sizeof(struct vmx_msr_entry) - 1)))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
While the SDM doesn't explicitly state an illegal count results in VM-Fail,
the SDM states that exceeding the limit may result in undefined behavior.
I.e. the SDM gives hardware, and thus KVM, carte blanche to do literally
anything in response to a count that exceeds the "recommended" limit.
If the limit is exceeded, undefined processor behavior may result
(including a machine check during the VMX transition).
KVM already enforces the limit when processing the MSRs, i.e. already
signals a late VM-Exit Consistency Check for VM-Enter, and generates a
VMX Abort for VM-Exit. I.e. explicitly checking the limits simply means
KVM will signal VM-Fail instead of VM-Exit or VMX Abort.
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/44961459-2759-4164-b604-f6bd43da8ce9@stanley.mountain
Link: https://lore.kernel.org/r/20250315024402.2363098-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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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 reStructuredText 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.