diff options
| author | Sean Christopherson <seanjc@google.com> | 2022-12-20 15:42:24 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-12-23 12:16:49 -0500 |
| commit | 057b18756b464729bc787ed4e6b44abb9f5c3a38 (patch) | |
| tree | 9f7e85ac843dfb58fe3e6a12aea47f86981c1a03 /arch/x86/kvm | |
| parent | 53800f88d414525d3fdc5c84629faa0b6bc35b3b (diff) | |
| download | linux-057b18756b464729bc787ed4e6b44abb9f5c3a38.tar.bz2 | |
KVM: nVMX: Document that ignoring memory failures for VMCLEAR is deliberate
Explicitly drop the result of kvm_vcpu_write_guest() when writing the
"launch state" as part of VMCLEAR emulation, and add a comment to call
out that KVM's behavior is architecturally valid. Intel's pseudocode
effectively says that VMCLEAR is a nop if the target VMCS address isn't
in memory, e.g. if the address points at MMIO.
Add a FIXME to call out that suppressing failures on __copy_to_user() is
wrong, as memory (a memslot) does exist in that case. Punt the issue to
the future as open coding kvm_vcpu_write_guest() just to make sure the
guest dies with -EFAULT isn't worth the extra complexity. The flaw will
need to be addressed if KVM ever does something intelligent on uaccess
failures, e.g. to support post-copy demand paging, but in that case KVM
will need a more thorough overhaul, i.e. VMCLEAR shouldn't need to open
code a core KVM helper.
No functional change intended.
Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527765 ("Error handling issues")
Fixes: 587d7e72aedc ("kvm: nVMX: VMCLEAR should not cause the vCPU to shut down")
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221220154224.526568-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/vmx/nested.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index b6f4411b613e..f18f3a9f0943 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -5296,10 +5296,19 @@ static int handle_vmclear(struct kvm_vcpu *vcpu) if (vmptr == vmx->nested.current_vmptr) nested_release_vmcs12(vcpu); - kvm_vcpu_write_guest(vcpu, - vmptr + offsetof(struct vmcs12, - launch_state), - &zero, sizeof(zero)); + /* + * Silently ignore memory errors on VMCLEAR, Intel's pseudocode + * for VMCLEAR includes a "ensure that data for VMCS referenced + * by the operand is in memory" clause that guards writes to + * memory, i.e. doing nothing for I/O is architecturally valid. + * + * FIXME: Suppress failures if and only if no memslot is found, + * i.e. exit to userspace if __copy_to_user() fails. + */ + (void)kvm_vcpu_write_guest(vcpu, + vmptr + offsetof(struct vmcs12, + launch_state), + &zero, sizeof(zero)); } else if (vmx->nested.hv_evmcs && vmptr == vmx->nested.hv_evmcs_vmptr) { nested_release_evmcs(vcpu); } |