linux-kernel - Re: [PATCH 2/7] KVM: x86/mmu: Fix struct guest

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Date:   Thu, 6 Feb 2020 15:07:30 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] KVM: x86/mmu: Fix struct guest_walker arrays for
 5-level paging

On Thu, Feb 06, 2020 at 02:08:31PM -0800, Sean Christopherson wrote:
> Define PT_MAX_FULL_LEVELS as PT64_ROOT_MAX_LEVEL, i.e. 5, to fix shadow
> paging for 5-level guest page tables.  PT_MAX_FULL_LEVELS is used to
> size the arrays that track guest pages table information, i.e. using a
> "max levels" of 4 causes KVM to access garbage beyond the end of an
> array when querying state for level 5 entries.  E.g. FNAME(gpte_changed)
> will read garbage and most likely return %true for a level 5 entry,
> soft-hanging the guest because FNAME(fetch) will restart the guest
> instead of creating SPTEs because it thinks the guest PTE has changed.
> 
> Fixes: 855feb673640 ("KVM: MMU: Add 5 level EPT & Shadow page table support.")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/mmu/paging_tmpl.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 4e1ef0473663..6b15b58f3ecc 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -33,7 +33,7 @@
>  	#define PT_GUEST_ACCESSED_SHIFT PT_ACCESSED_SHIFT
>  	#define PT_HAVE_ACCESSED_DIRTY(mmu) true
>  	#ifdef CONFIG_X86_64
> -	#define PT_MAX_FULL_LEVELS 4
> +	#define PT_MAX_FULL_LEVELS PT64_ROOT_MAX_LEVEL
>  	#define CMPXCHG cmpxchg
>  	#else
>  	#define CMPXCHG cmpxchg64
> @@ -66,7 +66,7 @@
>  	#define PT_GUEST_ACCESSED_SHIFT 8
>  	#define PT_HAVE_ACCESSED_DIRTY(mmu) ((mmu)->ept_ad)
>  	#define CMPXCHG cmpxchg64
> -	#define PT_MAX_FULL_LEVELS 4
> +	#define PT_MAX_FULL_LEVELS PT64_ROOT_MAX_LEVEL

Doh, the nested EPT change belongs in the next patch.  I'll retest tomorrow
and send a v2 when by brain is less mushy.

>  #else
>  	#error Invalid PTTYPE value
>  #endif
> -- 
> 2.24.1
>