[SRU][Artful][PATCH 1/1] KVM: VMX: remove I/O port 0x80 bypass on Intel hosts

Kleber Souza kleber.souza at canonical.com
Mon Feb 5 10:17:52 UTC 2018


Hi Khaled,

On 01/26/18 17:57, Kleber Sacilotto de Souza wrote:
> From: Andrew Honig <ahonig at google.com>
> 
> This fixes CVE-2017-1000407.

I noticed that the above line has been removed on the commit pushed to
artful tree. This line comes from the mainline commit and we tend not to
remove anything from the original commit message when applying it to our
trees, that's why I had the line with the CVE number below the original
provenance block. If you used our maint-modify-patch tool to add the CVE
number, it always add it to the first line of the commit message, so in
that case it would be OK to keep both lines at the top.

Thanks,
Kleber

> 
> KVM allows guests to directly access I/O port 0x80 on Intel hosts.  If
> the guest floods this port with writes it generates exceptions and
> instability in the host kernel, leading to a crash.  With this change
> guest writes to port 0x80 on Intel will behave the same as they
> currently behave on AMD systems.
> 
> Prevent the flooding by removing the code that sets port 0x80 as a
> passthrough port.  This is essentially the same as upstream patch
> 99f85a28a78e96d28907fe036e1671a218fee597, except that patch was
> for AMD chipsets and this patch is for Intel.
> 
> Signed-off-by: Andrew Honig <ahonig at google.com>
> Signed-off-by: Jim Mattson <jmattson at google.com>
> Fixes: fdef3ad1b386 ("KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs")
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Radim Krčmář <rkrcmar at redhat.com>
> 
> CVE-2017-1000407
> (cherry picked from commit d59d51f088014f25c2562de59b9abff4f42a7468)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> ---
>  arch/x86/kvm/vmx.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index cb044cd17790..2a4bf9e267d8 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6599,12 +6599,7 @@ static __init int hardware_setup(void)
>  	memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
>  	memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
>  
> -	/*
> -	 * Allow direct access to the PC debug port (it is often used for I/O
> -	 * delays, but the vmexits simply slow things down).
> -	 */
>  	memset(vmx_io_bitmap_a, 0xff, PAGE_SIZE);
> -	clear_bit(0x80, vmx_io_bitmap_a);
>  
>  	memset(vmx_io_bitmap_b, 0xff, PAGE_SIZE);
>  
> 




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