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Message-Id: <1509510743-28429-1-git-send-email-me@tobin.cc>
Date: Wed, 1 Nov 2017 15:32:21 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: kernel-hardening@...ts.openwall.com
Cc: "Tobin C. Harding" <me@...in.cc>,
"Jason A. Donenfeld" <Jason@...c4.com>,
Theodore Ts'o <tytso@....edu>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Tycho Andersen <tycho@...ker.com>,
"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>,
Joe Perches <joe@...ches.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>,
linux-kernel@...r.kernel.org
Subject: [PATCH V10 0/2] printk: hash addresses printed with %p
Currently there are many places in the kernel where addresses are being
printed using an unadorned %p. Kernel pointers should be printed using
%pK allowing some control via the kptr_restrict sysctl. Exposing
addresses gives attackers sensitive information about the kernel layout
in memory.
We can reduce the attack surface by hashing all addresses printed with
%p. This will of course break some users, forcing code printing needed
addresses to be updated.
This version adds testing, this is my first effort at kernel unit
testing. Modules in `lib` don't seem contained within a selftest target
so in order to incrementally develop the tests I implemented the tests
in `lib/test_printf.c`, built with `make M=lib` and then to insert the
module, instead of running selftest, I spun up a VM and inserted the
module manually. Comments or suggestions much appreciated.
Here is the behaviour that this series implements.
For kpt_restrict==0
Randomness not ready:
printed with %p: (ptrval) # NOTE: with padding
Valid pointer:
printed with %pK: deadbeefdeadbeef
printed with %p: 00000000deadbeef
malformed specifier (eg %i): 00000000deadbeef
NULL pointer:
printed with %pK: 0000000000000000
printed with %p: (null) # NOTE: with padding
malformed specifier (eg %i): (null)
For kpt_restrict==2
Valid pointer:
printed with %pK: 0000000000000000
All other output as for kptr_restrict==0
V10:
- Add patch so KASAN uses %pK instead of %p.
- Add documentation to Documentation/printk-formats.txt
- Add tests to lib/test_printf.c
- Change "(pointer value)" -> "(ptrval)" to fit within columns on 32
bit machines.
V9:
- Drop the initial patch from V8, leaving null pointer handling as is.
- Print the hashed ID _without_ a '0x' suffix.
- Mask the first 32 bits of the hashed ID to all zeros on 64 bit
architectures.
V8:
- Add second patch cleaning up null pointer printing in pointer()
- Move %pK handling to separate function, further cleaning up pointer()
- Move ptr_to_id() call outside of switch statement making hashing
the default behaviour (including malformed specifiers).
- Remove use of static_key, replace with simple boolean.
V7:
- Use tabs instead of spaces (ouch!).
V6:
- Use __early_initcall() to fill the SipHash key.
- Use static keys to guard hashing before the key is available.
V5:
- Remove spin lock.
- Add Jason A. Donenfeld to CC list by request.
- Add Theodore Ts'o to CC list due to comment on previous version.
V4:
- Remove changes to siphash.{ch}
- Do word size check, and return value cast, directly in ptr_to_id().
- Use add_ready_random_callback() to guard call to get_random_bytes()
V3:
- Use atomic_xchg() to guard setting [random] key.
- Remove erroneous white space change.
V2:
- Use SipHash to do the hashing.
The discussion related to this patch has been fragmented. There are
three threads associated with this patch. Email threads by subject:
[PATCH] printk: hash addresses printed with %p
[PATCH 0/3] add %pX specifier
[kernel-hardening] [RFC V2 0/6] add more kernel pointer filter options
Tobin C. Harding (2):
kasan: use %pK to print addresses instead of %p
printk: hash addresses printed with %p
Documentation/printk-formats.txt | 17 +++-
lib/test_printf.c | 108 +++++++++++++++---------
lib/vsprintf.c | 176 ++++++++++++++++++++++++++++-----------
mm/kasan/report.c | 8 +-
4 files changed, 217 insertions(+), 92 deletions(-)
--
2.7.4
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