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Re: [Xen-devel] [PATCH] VMX: make vmx_read_guest_msr() cope with callers not checking its return value


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 15 Aug 2018 12:39:36 +0100
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  • Cc: Kevin Tian <kevin.tian@xxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>
  • Delivery-date: Wed, 15 Aug 2018 11:39:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 15/08/18 12:34, Jan Beulich wrote:
> It took till the 4.5 backports of the L1TF prereqs that gcc 8.2 finally
> noticed that the vPMU callers, not checking the function's return value,
> may consume uninitialized data. Guard against this by storing zero on
> the error path.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

vPMU really is the gift which keeps on giving...

>
> --- a/xen/include/asm-x86/hvm/vmx/vmcs.h
> +++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
> @@ -586,7 +586,10 @@ static inline int vmx_read_guest_msr(con
>      const struct vmx_msr_entry *ent = vmx_find_msr(v, msr, VMX_MSR_GUEST);
>  
>      if ( !ent )
> +    {
> +        *val = 0;
>          return -ESRCH;
> +    }
>  
>      *val = ent->data;
>  

You want a similar adjustment in vmx_read_guest_loadonly_msr()
immediately below, which I believe is only applicable to staging atm.

With that, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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