linux-kernel - Re: [PATCH v2 2/2] Revert "KVM: x86: work around leak of uninitialized stack contents"

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Date:   Fri, 5 Jun 2020 19:33:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] Revert "KVM: x86: work around leak of
 uninitialized stack contents"

On 05/06/20 13:59, Vitaly Kuznetsov wrote:
> handle_vmptrst()/handle_vmread() stopped injecting #PF unconditionally
> and switched to nested_vmx_handle_memory_failure() which just kills the
> guest with KVM_EXIT_INTERNAL_ERROR in case of MMIO access, zeroing
> 'exception' in kvm_write_guest_virt_system() is not needed anymore.
> 
> This reverts commit 541ab2aeb28251bf7135c7961f3a6080eebcc705.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9e41b5135340..0097a97d331f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5647,13 +5647,6 @@ int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val,
>  	/* kvm_write_guest_virt_system can pull in tons of pages. */
>  	vcpu->arch.l1tf_flush_l1d = true;
>  
> -	/*
> -	 * FIXME: this should call handle_emulation_failure if X86EMUL_IO_NEEDED
> -	 * is returned, but our callers are not ready for that and they blindly
> -	 * call kvm_inject_page_fault.  Ensure that they at least do not leak
> -	 * uninitialized kernel stack memory into cr2 and error code.
> -	 */
> -	memset(exception, 0, sizeof(*exception));
>  	return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
>  					   PFERR_WRITE_MASK, exception);
>  }
> 

Queued, thanks.

Paolo