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authorSean Christopherson <seanjc@google.com>2022-12-20 15:42:24 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2022-12-23 12:16:49 -0500
commit057b18756b464729bc787ed4e6b44abb9f5c3a38 (patch)
tree9f7e85ac843dfb58fe3e6a12aea47f86981c1a03 /arch/x86/kvm
parent53800f88d414525d3fdc5c84629faa0b6bc35b3b (diff)
downloadlinux-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.c17
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);
}