4.14-stable review patch. If anyone has any objections, please let me know.
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From: Cfir Cohen cfir@google.com
commit c2dd5146e9fe1f22c77c1b011adf84eea0245806 upstream.
nested_get_vmcs12_pages() processes the posted_intr address in vmcs12. It caches the kmap()ed page object and pointer, however, it doesn't handle errors correctly: it's possible to cache a valid pointer, then release the page and later dereference the dangling pointer.
I was able to reproduce with the following steps:
1. Call vmlaunch with valid posted_intr_desc_addr but an invalid MSR_EFER. This causes nested_get_vmcs12_pages() to cache the kmap()ed pi_desc_page and pi_desc. Later the invalid EFER value fails check_vmentry_postreqs() which fails the first vmlaunch.
2. Call vmlanuch with a valid EFER but an invalid posted_intr_desc_addr (I set it to 2G - 0x80). The second time we call nested_get_vmcs12_pages pi_desc_page is unmapped and released and pi_desc_page is set to NULL (the "shouldn't happen" clause). Due to the invalid posted_intr_desc_addr, kvm_vcpu_gpa_to_page() fails and nested_get_vmcs12_pages() returns. It doesn't return an error value so vmlaunch proceeds. Note that at this time we have a dangling pointer in vmx->nested.pi_desc and POSTED_INTR_DESC_ADDR in L0's vmcs.
3. Issue an IPI in L2 guest code. This triggers a call to vmx_complete_nested_posted_interrupt() and pi_test_and_clear_on() which dereferences the dangling pointer.
Vulnerable code requires nested and enable_apicv variables to be set to true. The host CPU must also support posted interrupts.
Fixes: 5e2f30b756a37 "KVM: nVMX: get rid of nested_get_page()" Cc: stable@vger.kernel.org Reviewed-by: Andy Honig ahonig@google.com Signed-off-by: Cfir Cohen cfir@google.com Reviewed-by: Liran Alon liran.alon@oracle.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/vmx.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -10447,6 +10447,8 @@ static void nested_get_vmcs12_pages(stru kunmap(vmx->nested.pi_desc_page); kvm_release_page_dirty(vmx->nested.pi_desc_page); vmx->nested.pi_desc_page = NULL; + vmx->nested.pi_desc = NULL; + vmcs_write64(POSTED_INTR_DESC_ADDR, -1ull); } page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->posted_intr_desc_addr); if (is_error_page(page))