linux-kernel - Re: [PATCH 18/20] objtool: Add UACCESS validation

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Date:   Mon, 11 Mar 2019 13:01:39 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, luto@...nel.org,
        bp@...en8.de, dvlasenk@...hat.com, linux-kernel@...r.kernel.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: Re: [PATCH 18/20] objtool: Add UACCESS validation

On Sun, Mar 10, 2019 at 02:10:46PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 08, 2019 at 03:02:09PM -0600, Josh Poimboeuf wrote:
> 
> > These gotos make my head spin.  Again I would much prefer a small amount
> > of code duplication over this.
> 
> something like so then?

Yeah, that looks a lot nicer to me.  Thanks.

> 
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1888,6 +1888,23 @@ static inline const char *insn_dest_name
>  	return "{dynamic}";
>  }
>  
> +static int validate_call(struct instruction *insn, struct insn_state *state)
> +{
> +	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
> +		WARN_FUNC("call to %s() with UACCESS enabled",
> +				insn->sec, insn->offset, insn_dest_name(insn));
> +		return 1;
> +	}
> +
> +	if (state->df) {
> +		WARN_FUNC("call to %s() with DF set",
> +				insn->sec, insn->offset, insn_dest_name(insn));
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Follow the branch starting at the given instruction, and recursively follow
>   * any other branches (jumps).  Meanwhile, track the frame pointer state at
> @@ -2036,25 +2053,9 @@ static int validate_branch(struct objtoo
>  
>  		case INSN_CALL:
>  		case INSN_CALL_DYNAMIC:
> -do_call:
> -			if (state.uaccess && !func_uaccess_safe(insn->call_dest)) {
> -				WARN_FUNC("call to %s() with UACCESS enabled",
> -					  sec, insn->offset, insn_dest_name(insn));
> -				return 1;
> -			}
> -
> -			if (state.df) {
> -				WARN_FUNC("call to %s() with DF set",
> -					  sec, insn->offset, insn_dest_name(insn));
> -				return 1;
> -			}
> -
> -			if (insn->type == INSN_JUMP_UNCONDITIONAL ||
> -			    insn->type == INSN_JUMP_DYNAMIC)
> -				return 0;
> -
> -			if (insn->type == INSN_JUMP_CONDITIONAL)
> -				break;
> +			ret = validate_call(insn, &state);
> +			if (ret)
> +				return ret;
>  
>  			if (insn->type == INSN_CALL) {
>  				if (is_fentry_call(insn))
> @@ -2077,13 +2078,15 @@ static int validate_branch(struct objtoo
>  		case INSN_JUMP_CONDITIONAL:
>  		case INSN_JUMP_UNCONDITIONAL:
>  			if (func && !insn->jump_dest) {
> -do_sibling_call:
> +				/* sibling call */
>  				if (has_modified_stack_frame(&state)) {
>  					WARN_FUNC("sibling call from callable instruction with modified stack frame",
>  							sec, insn->offset);
>  					return 1;
>  				}
> -				goto do_call;
> +				ret = validate_call(insn, &state);
> +				if (ret)
> +					return ret;
>  
>  			} else if (insn->jump_dest &&
>  				   (!func || !insn->jump_dest->func ||
> @@ -2104,8 +2107,17 @@ static int validate_branch(struct objtoo
>  			break;
>  
>  		case INSN_JUMP_DYNAMIC:
> -			if (func && list_empty(&insn->alts))
> -				goto do_sibling_call;
> +			if (func && list_empty(&insn->alts)) {
> +				/* sibling call */
> +				if (has_modified_stack_frame(&state)) {
> +					WARN_FUNC("sibling call from callable instruction with modified stack frame",
> +							sec, insn->offset);
> +					return 1;
> +				}
> +				ret = validate_call(insn, &state);
> +				if (ret)
> +					return ret;
> +			}
>  
>  			return 0;
>  
> 

-- 
Josh