linux-kernel - Re: [PATCH v2 3/3] checkpatch: warn for use of %px

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Date:   Fri, 8 Dec 2017 08:06:53 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Joe Perches <joe@...ches.com>
Cc:     Andy Whitcroft <apw@...onical.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] checkpatch: warn for use of %px

On Wed, Dec 06, 2017 at 02:37:08PM +1100, Tobin C. Harding wrote:
> Usage of the new %px specifier potentially leaks sensitive
> inforamtion. Printing kernel addresses exposes the kernel layout in
> memory, this is potentially exploitable. We have tools in the kernel to
> help us do the right thing. We can have checkpatch warn developers of
> potential dangers of using %px.
> 
> Have checkpatch emit a warning for usage of specifier %px.
> 
> Signed-off-by: Tobin C. Harding <me@...in.cc>
> Co-developed-by: Joe Perches <joe@...ches.com>

  Co-Developed-by:

Woops.

Joe I didn't quite understand what you meant when you said that this
could go in via any tree. I'm still learning the whole kernel tree
management thing. Don't checkpatch patches go in via Andy's tree?

https://git.kernel.org/pub/scm/linux/kernel/git/apw/checkpatch.git/

In any case, please drop this set. I'll fix the tag and re-spin.

thanks,
Tobin.

> Acked-by: Joe Perches <joe@...ches.com>
> ---
>  scripts/checkpatch.pl | 31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 4534c9a9aefa..6df99d1ebca5 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -5750,21 +5750,38 @@ sub process {
>  		    defined $stat &&
>  		    $stat =~ /^\+(?![^\{]*\{\s*).*\b(\w+)\s*\(.*$String\s*,/s &&
>  		    $1 !~ /^_*volatile_*$/) {
> -			my $bad_extension = "";
> +			my $specifier;
> +			my $extension;
> +			my $bad_specifier = "";
> +			my $stat_real;
> +
>  			my $lc = $stat =~ tr@\n@@;
>  			$lc = $lc + $linenr;
>  		        for (my $count = $linenr; $count <= $lc; $count++) {
>  				my $fmt = get_quoted_string($lines[$count - 1], raw_line($count, 0));
>  				$fmt =~ s/%%//g;
> -				if ($fmt =~ /(\%[\*\d\.]*p(?![\WFfSsBKRraEhMmIiUDdgVCbGNOx]).)/) {
> -					$bad_extension = $1;
> -					last;
> +
> +				while ($fmt =~ /(\%[\*\d\.]*p(\w))/g) {
> +					$specifier = $1;
> +					$extension = $2;
> +					if ($extension !~ /[FfSsBKRraEhMmIiUDdgVCbGNOx]/) {
> +						$bad_specifier = $specifier;
> +						last;
> +					}
> +					if ($extension eq "x" && !defined($stat_real)) {
> +						if (!defined($stat_real)) {
> +							$stat_real = get_stat_real($linenr, $lc);
> +						}
> +						WARN("VSPRINTF_SPECIFIER_PX",
> +						     "Using vsprintf specifier '\%px' potentially exposes the kernel memory layout, if you don't really need the address please consider using '\%p'.\n" . "$here\n$stat_real\n");
> +					}
>  				}
> +
>  			}
> -			if ($bad_extension ne "") {
> -				my $stat_real = get_stat_real($linenr, $lc);
> +			if ($bad_specifier ne "") {
> +				$stat_real = get_stat_real($linenr, $lc);
>  				WARN("VSPRINTF_POINTER_EXTENSION",
> -				     "Invalid vsprintf pointer extension '$bad_extension'\n" . "$here\n$stat_real\n");
> +				     "Invalid vsprintf pointer extension '$bad_specifier'\n" . "$here\n$stat_real\n");
>  			}
>  		}
>  
> -- 
> 2.7.4
>