Re: [PATCH] Fix UB in ipa-polymorphic-call.c (PR tree-optimization/81603)

[Richard Biener <rguenther@suse.de>]

On Mon, 31 Jul 2017, Jakub Jelinek wrote:

> Hi!
> 
> ipa_polymorphic_call_context offset field is in bits (for whatever reason),
> and the following computations can overflow and invoke UB.
> This patch computes it in offset_int instead and punts if there is overflow.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok.  As said in the PR the machinery should probably use byte offsets
throughout (do we support any target where HWI < size of ptr_mode?  That 
is, 128bit pointers?)

Richard.

> 2017-07-31  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/81603
> 	* ipa-polymorphic-call.c
> 	(ipa_polymorphic_call_context::ipa_polymorphic_call_context): Perform
> 	offset arithmetic in offset_int, bail out if the resulting bit offset
> 	doesn't fit into shwi.
> 
> --- gcc/ipa-polymorphic-call.c.jj	2017-06-12 12:41:55.000000000 +0200
> +++ gcc/ipa-polymorphic-call.c	2017-07-28 15:02:43.747354910 +0200
> @@ -921,9 +921,13 @@ ipa_polymorphic_call_context::ipa_polymo
>  		 and MEM_REF is meaningless, but we can look futher.  */
>  	      if (TREE_CODE (base) == MEM_REF)
>  		{
> +		  offset_int o = mem_ref_offset (base) * BITS_PER_UNIT;
> +		  o += offset;
> +		  o += offset2;
> +		  if (!wi::fits_shwi_p (o))
> +		    break;
>  		  base_pointer = TREE_OPERAND (base, 0);
> -		  offset
> -		    += offset2 + mem_ref_offset (base).to_short_addr () * BITS_PER_UNIT;
> +		  offset = o.to_shwi ();
>  		  outer_type = NULL;
>  		}
>  	      /* We found base object.  In this case the outer_type
> @@ -961,10 +965,15 @@ ipa_polymorphic_call_context::ipa_polymo
>  	    break;
>  	}
>        else if (TREE_CODE (base_pointer) == POINTER_PLUS_EXPR
> -	       && tree_fits_uhwi_p (TREE_OPERAND (base_pointer, 1)))
> +	       && TREE_CODE (TREE_OPERAND (base_pointer, 1)) == INTEGER_CST)
>  	{
> -	  offset += tree_to_shwi (TREE_OPERAND (base_pointer, 1))
> -		    * BITS_PER_UNIT;
> +	  offset_int o = offset_int::from (TREE_OPERAND (base_pointer, 1),
> +					   SIGNED);
> +	  o *= BITS_PER_UNIT;
> +	  o += offset;
> +	  if (!wi::fits_shwi_p (o))
> +	    break;
> +	  offset = o.to_shwi ();
>  	  base_pointer = TREE_OPERAND (base_pointer, 0);
>  	}
>        else
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)