linux-kernel - Re: [PATCH] tracing: do not leak kernel addresses

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Date:   Thu, 26 Jul 2018 18:15:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     greg@...ah.com, Kees Cook <keescook@...gle.com>,
        salyzyn@...roid.com, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, kernel-team@...roid.com, stable@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] tracing: do not leak kernel addresses

On Thu, 26 Jul 2018 09:52:11 -0700
Nick Desaulniers <ndesaulniers@...gle.com> wrote:

> See the section "Kernel addresses" in
> Documentation/security/self-protection.  IIRC, the issue is that a
> process may have CAP_SYSLOG but not necessarily CAP_SYS_ADMIN (so it
> can read dmesg, but not necessarily issue a sysctl to change
> kptr_restrict), get compromised and used to leak kernel addresses,
> which can then be used to defeat KASLR.

But the code doesn't go to dmesg. It's only available
via /sys/kernel/debug/tracing/printk_formats which is only available
via root. Nobody else has access to that directory.

-- Steve