Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

Joe Perches
2017-11-30T03:58:35Z

On Thu, 2017-11-30 at 10:26 +1100, Tobin C. Harding wrote:
> On Wed, Nov 29, 2017 at 03:20:58PM -0800, Andrew Morton wrote:
> > On Wed, 29 Nov 2017 13:05:04 +1100 "Tobin C. Harding" <me@tobin.cc> wrote:
> >
> > > 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.

> By stern, you mean use stern language?

I hope he doesn't mean tweet.

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");