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Message-ID: <20130406101037.GA3612@pd.tnic>
Date: Sat, 6 Apr 2013 12:10:37 +0200
From: Borislav Petkov <bp@...en8.de>
To: Kees Cook <keescook@...omium.org>
Cc: Julien Tinnes <jln@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "x86@...nel.org" <x86@...nel.org>,
Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
Matthew Garrett <mjg@...hat.com>,
Matt Fleming <matt.fleming@...el.com>,
Eric Northup <digitaleric@...gle.com>,
Dan Rosenberg <drosenberg@...curity.com>,
Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR
On Fri, Apr 05, 2013 at 04:18:49PM -0700, Kees Cook wrote:
> There is already a hook in the patch that prints the offset:
>
> +dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
> +{
> + pr_emerg("Kernel Offset: 0x%lx\n",
> + (unsigned long)&_text - __START_KERNEL);
> ...
> + atomic_notifier_chain_register(&panic_notifier_list,
> + &kernel_offset_notifier);
>
> But of course, this can get improved.
Yeah, this should probably be added to dump_trace(), i.e. something
which walks stack frames and dumps addresses. Because, in the panic
notifier, you're missing all those WARN* callsites, for example.
Also, I wonder whether it wouldn't be too hard to go even a step further
and compute the original, linker vmlinux addresses from the offsets
and dump a stack trace which looks exactly the same as if KASLR is
off. It'll probably need something to say KASLR was on when the trace
happened, though:
[ 790.253365] Call Trace (KASLR):
[ 790.254121] [<ffffffff8110bc90>] ? __smpboot_create_thread+0x180/0x180
[ 790.255428] [<ffffffff810ff1df>] kthread+0xef/0x100
...
so that people who stare at this, know.
Because, in that case, you don't need both the panic notifier or the
userspace script massaging stack trace output anymore.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
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