On Wed, Nov 29, 2017 at 08:41:36PM -0800, Joe Perches wrote:

On Thu, 2017-11-30 at 15:18 +1100, Tobin C. Harding wrote:

quoted

On Wed, Nov 29, 2017 at 07:58:26PM -0800, Joe Perches wrote:

quoted

On Thu, 2017-11-30 at 10:26 +1100, Tobin C. Harding wrote:

quoted

On Wed, Nov 29, 2017 at 03:20:58PM -0800, Andrew Morton wrote:

quoted

On Wed, 29 Nov 2017 13:05:04 +1100 "Tobin C. Harding" [off-list ref] wrote:

quoted

printk specifier %p now hashes all addresses before printing. Sometimes
we need to see the actual unmodified address. This can be achieved using
%lx but then we face the risk that if in future we want to change the
way the Kernel handles printing of pointers we will have to grep through
the already existent 50 000 %lx call sites. Let's add specifier %px as a
clear, opt-in, way to print a pointer and maintain some level of
isolation from all the other hex integer output within the Kernel.

Add printk specifier %px to print the actual unmodified address.

...

+Unmodified Addresses
+====================
+
+::
+
+	%px	01234567 or 0123456789abcdef
+
+For printing pointers when you _really_ want to print the address. Please
+consider whether or not you are leaking sensitive information about the
+Kernel layout in memory before printing pointers with %px. %px is
+functionally equivalent to %lx. %px is preferred to %lx because it is more
+uniquely grep'able. If, in the future, we need to modify the way the Kernel
+handles printing pointers it will be nice to be able to find the call
+sites.
+

You might want to add a checkpatch rule which emits a stern
do-you-really-want-to-do-this warning when someone uses %px.

Oh, nice idea. It has to be a CHECK but right?

No, it has to be something that's not --strict
so a WARN would probably be best.

quoted

By stern, you mean use stern language?

I hope he doesn't mean tweet.

/me says tweet tweet (like a bird)

quoted

Something like:
---
 scripts/checkpatch.pl | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0ce249f157a1..9d789cbe7df5 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl

@@ -5758,21 +5758,40 @@ sub process {
 		    defined $stat &&
 		    $stat =~ /^\+(?![^\{]*\{\s*).*\b(\w+)\s*\(.*$String\s*,/s &&
 		    $1 !~ /^_*volatile_*$/) {
+			my $complete_extension = "";
+			my $extension = "";
 			my $bad_extension = "";
 			my $lc = $stat =~ tr@\n@@;
 			$lc = $lc + $linenr;
+			my $stat_real;
 		        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(?![\WFfSsBKRraEhMmIiUDdgVCbGNO]).)/) {
-					$bad_extension = $1;
-					last;
+				while ($fmt =~ /(\%[\*\d\.]*p(\w))/g) {
+					$complete_extension = $1;
+					$extension = $2;
+					if ($extension !~ /[FfSsBKRraEhMmIiUDdgVCbGNOx]/) {
+						$bad_extension = $complete_extension;
+						last;
+					}
+					if ($extension eq "x") {
+						if (!defined($stat_real)) {
+							$stat_real = raw_line($linenr, 0);
+							for (my $count = $linenr + 1; $count <= $lc; $count++) {
+								$stat_real = $stat_real . "\n" . raw_line($count, 0);
+							}
+						}
+						WARN("VSPRINTF_POINTER_PX",
+						     "Using vsprintf pointer extension '$complete_extension' exposes kernel address for possible hacking\n" . "$here\n$stat_real\n");
+					}
 				}
 			}
 			if ($bad_extension ne "") {
-				my $stat_real = raw_line($linenr, 0);
-				for (my $count = $linenr + 1; $count <= $lc; $count++) {
-					$stat_real = $stat_real . "\n" . raw_line($count, 0);
+				if (!defined($stat_real)) {
+					$stat_real = raw_line($linenr, 0);
+					for (my $count = $linenr + 1; $count <= $lc; $count++) {
+						$stat_real = $stat_real . "\n" . raw_line($count, 0);
+					}
 				}
 				WARN("VSPRINTF_POINTER_EXTENSION",
 				     "Invalid vsprintf pointer extension '$bad_extension'\n" . "$here\n$stat_real\n");

Awesome. So moving forward, I should apply this code. Test it,

I didn't sign it and just trivially tested it.

So test it locally, see if it doesn't work
and check if the wording could be improved.

One possible negative is that if the format
contains multiple %px uses, then each use is
warned.

Maybe it should be
				if ($extension eq "x" && !defined($stat_real)) {
					...
					WARN("VSPRINTF_POINTER_PX", ...)
				}
so that only the first %px is warned.

Ok, will do as suggested.

If/when the %px series is applied, then this
can go in via whatever tree.

The %px series is in Linus' mainline now. I'll get this stuff to you and
Andy for ack'ing (and LKML) soon as its done.

thanks,
Tobin.