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Re: [PATCH] x86/pv: Sanity check bytes_per_rep in rep_outs()


  • To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 14 May 2024 09:22:38 +0200
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 14 May 2024 07:22:40 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 14.05.2024 09:05, Roger Pau Monné wrote:
> On Sat, May 11, 2024 at 04:16:42PM +0100, Andrew Cooper wrote:
>> Architecturally, there's no 64-bit variant of OUTS in x86.

This is the reason why personally ...

>>  Leaving an
>> assertion to this effect is enough to satisfy the analyser.

... I view adding such, in particular ...

>> --- a/xen/arch/x86/pv/emul-priv-op.c
>> +++ b/xen/arch/x86/pv/emul-priv-op.c
>> @@ -685,6 +685,8 @@ static int cf_check rep_outs(
>>  
>>      *reps = 0;
>>  
>> +    ASSERT(bytes_per_rep <= 4); /* i.e. 'data' being 4 bytes is fine. */
> 
> Don't we need this to be a BUG_ON() to satisfy the compiler also on
> non-debug builds?
> 
> Or maybe:
> 
> if ( bytes_per_rep > 4 )
> {
>     ASSERT_UNREACHABLE();
>     return X86EMUL_UNHANDLEABLE;
> }

... such a non-debug-build-covering form as dead code. With suitable
information to hand, I guess Eclair / Misra might even say so, too.

Instead I view the analyzer report here as a weakness of how analysis
is (and has to be) done.

Jan

> Would it be possible to add the check to guest_io_okay() itself?
> 
> Thanks, Roger.




 


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