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From: Ingo Molnar <mingo@kernel.org>
To: Andi Kleen <ak@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	tglx@linutronix.de, x86@kernel.org, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	luto@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	torvalds@linux-foundation.org
Subject: Re: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels
Date: Tue, 6 Feb 2018 08:19:33 +0100	[thread overview]
Message-ID: <20180206071933.3rbyglzndtsxcu47@gmail.com> (raw)
In-Reply-To: <20180205155837.GK30338@tassilo.jf.intel.com>


* Andi Kleen <ak@linux.intel.com> wrote:

> >      - There's various conditional pieces of entry code that run before any 
> >        RBP-clobbering C function is called. While none of them has an exploitable 
> >        Spectre 'gadget' at the moment, we'd have to consider this for every future
> >        change.
> 
> The Frame Pointer is always set up in assembler too, just in another macro.

As I replied to Andy, that's not universally true: there are code paths where RBP 
is not set before calling C code or going into the more complex parts of the 
kernel entry code.

This RBP value leak in fact demonstrates the validity of my robustness argument:

> >   I.e. we cannot universally rely on RBP being sanitized. In _practice_ it 
> >   will be sanitized, but we don't know for sure without expending quite some 
> >   effort to think through all the cases.

Thanks,

	Ingo

  reply	other threads:[~2018-02-06  7:19 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-04 17:43 [PATCH v2 0/3] x86/entry: Clear registers to sanitize speculative usages Dan Williams
2018-02-04 17:44 ` [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels Dan Williams
2018-02-05 11:42   ` Ingo Molnar
2018-02-05 15:37     ` Andy Lutomirski
2018-02-05 16:30       ` Ingo Molnar
2018-02-05 16:37         ` Andy Lutomirski
2018-02-05 17:26           ` Josh Poimboeuf
2018-02-05 17:31             ` Andy Lutomirski
2018-02-05 17:48               ` Josh Poimboeuf
2018-02-05 15:58     ` Andi Kleen
2018-02-06  7:19       ` Ingo Molnar [this message]
2018-02-05 11:58   ` Ingo Molnar
2018-02-05 21:33     ` Dan Williams
2018-02-05 21:58       ` Linus Torvalds
2018-02-05 22:10         ` Andy Lutomirski
2018-02-05 22:19           ` Dan Williams
2018-02-05 22:22           ` Linus Torvalds
2018-02-05 22:25             ` Linus Torvalds
2018-02-04 17:44 ` [PATCH v2 2/3] x86/entry: Clear registers for 64bit exceptions/interrupts Dan Williams
2018-02-04 17:44 ` [PATCH v2 3/3] x86/entry: Clear registers for compat syscalls Dan Williams

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