Date: Wed, 18 Oct 2017 10:15:59 +1100 From: "Tobin C. Harding" <me@...in.cc> To: Steven Rostedt <rostedt@...dmis.org> Cc: kernel-hardening@...ts.openwall.com, 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 <will.deacon@....com>, 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: Re: [PATCH v2] printk: hash addresses printed with %p On Tue, Oct 17, 2017 at 09:31:19AM -0400, Steven Rostedt wrote: > On Tue, 17 Oct 2017 15:52:51 +1100 > "Tobin C. Harding" <me@...in.cc> wrote: > > > 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. > > > > For what it's worth, usage of unadorned %p can be broken down as follows > > > > git grep '%p[^KFfSsBRrbMmIiEUVKNhdDgCGO]' | wc -l > > Does %p[FfSs] leak addresses? Well, I guess it does if they are not > found in kallsyms, but otherwise you have: > > function+0x<offset> You are correct %pF and %pS print an offset. Does this provide an attack vector, I didn't think so but I'm no security expert. If they do then we need to amend those calls also. We still have %pa[pd] to see to as well obviously. thanks for the review, Tobin.
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