Re: [PATCH] KVM: Fix UAF in nested posted interrupt processing

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 18/12/18 17:18, Cfir Cohen wrote:
> 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()"
> Reviewed-by: Andy Honig <ahonig@xxxxxxxxxx>
> Signed-off-by: Cfir Cohen <cfir@xxxxxxxxxx>
> ---
>  arch/x86/kvm/vmx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 02edd9960e9d..8d5d984541be 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11985,6 +11985,8 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>  			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))
> 

Queued, thanks.

Paolo




[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux