Date: Tue, 7 Nov 2017 13:44:01 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Kees Cook <keescook@...omium.org> Cc: "Tobin C. Harding" <me@...in.cc>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Andy Lutomirski <luto@...nel.org>, Joe Perches <joe@...ches.com>, Network Development <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "Jason A. Donenfeld" <Jason@...c4.com>, "Theodore Ts'o" <tytso@....edu>, 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>, 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 Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v3] scripts: add leaking_addresses.pl On Tue, Nov 7, 2017 at 1:22 PM, Kees Cook <keescook@...omium.org> wrote: > > Linus, what do you have in mind for the root-only "yes we really need > the actual address output" exceptions? I am convinced that absolutely none of them should use '%pK'. So far we have actually never seen a valid case wher %pK was really the right thing to do. > For example, right now /sys/kernel/debug/kernel_page_tables > (CONFIG_X86_PTDUMP=y) needs actual address and currently uses %x. So I think it could continue to use %x, and just make sure the whole file is root-only. And that is why %pK is so wrong. It's almost never really about root. Look at /proc/kallsyms, for example. There it's mainly about kernel profiles (although there certainly have been other uses historically, and maybe some of them remain) - which we have another flag for entirely that is very much specifically about kernel profiles. > Looking other places that stand out, it seems like > /proc/lockdep_chains and /proc/lockdep (CONFIG_LOCKDEP=y) has a ton of > %p usage. It's unclear to me if a hash is sufficient for meaningful > debugging there? Maybe not, but that is also _so_ esoteric that I suspect the right fix is to just make it root-only readable. I've never used it, we should check with people who have. I get the feeling that this is purely for PeterZ debugging. The very first commit that introduced that code actually has a (FIXME: should go into debugfs) so I suspect it never should have been user-readable to begin with. I guess it makes some things easier, but it really is *very* different from things like profiling. Profiling you often *cannot* do as root - some things you profile really shouldn't be run as root, and might even refuse to do so. So requiring you to be root just to get a kernel profile is very bad. But looking at lockdep stats? Yeah, 'sudo' isn't so big of a deal. And I really suspect that's true of a _lot_ of these %p things that really want a pointer. It's not that they really want %pK, it's that they shouldn't have been visible to regular users in the first place. Things that *do* want a pointer and should be visible to regular users are things like oops messages etc, but even there we obviously generally want to use %pS/%pF when possible (but generally %x when not - things like register contents etc that *may* contain pointers). And if they really are visible to users - because you want to cross-correlate them for things like netstat - I think the hashing is the right thing to do both for root and for regular users. > Seems like these three from dmesg could be removed? > > [ 0.000000] Base memory trampoline at [ffffa3fc40099000] 99000 size 24576 > arch/x86/realmode/init.c > > [ 0.000000] percpu: Embedded 38 pages/cpu @ffffa4007fc00000 s116944 > r8192 d30512 u524288 > mm/percpu.c > > [ 0.456395] software IO TLB [mem 0xbbfdf000-0xbffdf000] (64MB) > mapped at [ffffa3fcfbfdf000-ffffa3fcfffdefff] > lib/swiotlb.c Yes, I think the solution for a lot of the random device discovery messages etc is to just remove them. They were likely useful when the code was new and untested, and just stayed around afterwards. Linus
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