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Date: Thu, 30 Nov 2017 15:18:24 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: Joe Perches <joe@...ches.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
kernel-hardening@...ts.openwall.com,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Jason A. Donenfeld" <Jason@...c4.com>,
Theodore Ts'o <tytso@....edu>,
Kees Cook <keescook@...omium.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Tycho Andersen <tycho@...ho.ws>,
"Roberts, William C" <william.c.roberts@...el.com>,
Tejun Heo <tj@...nel.org>,
Jordan Glover <Golden_Miller83@...tonmail.ch>,
Greg KH <gregkh@...uxfoundation.org>,
Petr Mladek <pmladek@...e.com>,
Ian Campbell <ijc@...lion.org.uk>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <wilal.deacon@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Chris Fries <cfries@...gle.com>,
Dave Weinstein <olorin@...gle.com>,
Daniel Micay <danielmicay@...il.com>,
Djalal Harouni <tixxdz@...il.com>,
Radim Krčmář <rkrcmar@...hat.com>,
linux-kernel@...r.kernel.org,
Network Development <netdev@...r.kernel.org>,
David Miller <davem@...emloft.net>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH V11 4/5] vsprintf: add printk specifier %px
On Wed, Nov 29, 2017 at 07:58:26PM -0800, Joe Perches wrote:
> 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@...in.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.
/me says tweet tweet (like a bird)
> 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, commit it
with a log message stating you wrote it and I just tested it then submit
the patch, right?
thanks,
Tobin.
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