linux-kernel - Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl

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Message-ID: <CAADWXX8guqt=Yz-Lo+qU6Ed0t-mG-B=UkqSDaSr3bH+Q2aOn-Q@mail.gmail.com>
Date:   Thu, 5 Mar 2020 12:51:33 -0600
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Scott Wood <oss@...error.net>
Cc:     Kees Cook <keescook@...omium.org>, Jason Yan <yanaijie@...wei.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        lkml <linux-kernel@...r.kernel.org>,
        "Tobin C . Harding" <tobin@...nel.org>,
        Daniel Axtens <dja@...ens.net>
Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64

On Wed, Mar 4, 2020 at 3:16 PM Scott Wood <oss@...error.net> wrote:
>
> The frustration is with the inability to set a flag to say, "I'm debugging and
> don't care about leaks... in fact I'd like as much information as possible to
> leak to me."

Well, I definitely don't want to tie it to "I turned off kaslr in
order to help debugging". That just means that now you're debugging a
kernel that is fundamentally different from what people are running.

So I'd much rather have people just set a really magic flag, perhaps
when kgdb is in use or something.

> In any case, this came up now due to a question about what to use when
> printing crash dumps.  PowerPC currently prints stack and return addresses
> with %lx (in addition to %pS in the latter case) and someone proposed
> converting them to %p and/or removing them altogether.

Please just use '%pS'.

The symbol and offset is what is useful when users send crash-dumps.
The hex value is entirely pointless with kaslr - which should
basically be the default.

Note that this isn't about security at that point - crash dumps are
something that shouldn't happen, but if they do happen, we want the
pointers. But the random hex value just isn't _useful_, so it's just
making things less legible.

                  Linus