From: Arvind Sankar <nivedita@alum.mit.edu>
To: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
the arch/x86 maintainers <x86@kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
LKML <linux-kernel@vger.kernel.org>,
Andrey Konovalov <andreyknvl@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>
Subject: Re: [RFC PATCH 1/2] lib/string: Disable instrumentation
Date: Tue, 8 Sep 2020 14:40:03 -0400 [thread overview]
Message-ID: <20200908184003.GA4164124@rani.riverdale.lan> (raw)
In-Reply-To: <202009081021.8E5957A1F@keescook>
On Tue, Sep 08, 2020 at 10:21:32AM -0700, Kees Cook wrote:
> On Tue, Sep 08, 2020 at 11:39:11AM +0200, Marco Elver wrote:
> > On Sun, 6 Sep 2020 at 00:23, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > String functions can be useful in early boot, but using instrumented
> > > versions can be problematic: eg on x86, some of the early boot code is
> > > executing out of an identity mapping rather than the kernel virtual
> > > addresses. Accessing any global variables at this point will lead to a
> > > crash.
> > >
> >
> > Ouch.
> >
> > We have found manifestations of bugs in lib/string.c functions, e.g.:
> > https://groups.google.com/forum/#!msg/syzkaller-bugs/atbKWcFqE9s/x7AtoVoBAgAJ
> > https://groups.google.com/forum/#!msg/syzkaller-bugs/iGBUm-FDhkM/chl05uEgBAAJ
> >
> > Is there any way this can be avoided?
>
> Agreed: I would like to keep this instrumentation; it's a common place
> to find bugs, security issues, etc.
>
> --
> Kees Cook
Ok, understood. I'll revise to open-code the strscpy instead.
Is instrumentation supported on x86-32? load_ucode_bsp() on 32-bit is
called before paging is enabled, and load_ucode_bsp() itself, along with
eg lib/earlycpio and lib/string that it uses, don't have anything to
disable instrumentation. kcov, kasan, kcsan are unsupported already on
32-bit, but the others like gcov and PROFILE_ALL_BRANCHES look like they
would just cause a crash if microcode loading is enabled.
next prev parent reply other threads:[~2020-09-08 18:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-05 22:23 [RFC PATCH 0/2] Allow use of lib/string in early boot Arvind Sankar
2020-09-05 22:23 ` [RFC PATCH 1/2] lib/string: Disable instrumentation Arvind Sankar
2020-09-08 9:39 ` Marco Elver
2020-09-08 17:21 ` Kees Cook
2020-09-08 18:40 ` Arvind Sankar [this message]
2020-09-09 5:20 ` Dmitry Vyukov
2020-09-05 22:23 ` [RFC PATCH 2/2] x86/cmdline: Use strscpy to initialize boot_command_line Arvind Sankar
2020-09-05 22:59 ` Randy Dunlap
2020-09-05 23:16 ` Arvind Sankar
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