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Date: Tue, 25 Apr 2017 13:26:43 +0200
From: "PaX Team" <pageexec@...email.hu>
To: Kees Cook <keescook@...omium.org>, Peter Zijlstra <peterz@...radead.org>
CC: linux-kernel@...r.kernel.org, Eric Biggers <ebiggers3@...il.com>,
Christoph Hellwig <hch@...radead.org>,
"axboe@...nel.dk" <axboe@...nel.dk>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Hans Liljestrand <ishkamiel@...il.com>,
David Windsor <dwindsor@...il.com>, x86@...nel.org,
Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jann Horn <jann@...jh.net>, davem@...emloft.net,
linux-arch@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling
On 25 Apr 2017 at 12:23, Peter Zijlstra wrote:
> So what avoids this:
simple, you noted it yourself in your previous mail:
> Well, your setup (panic_on_warn et al) would have it panic the box. That
> will effectively stop the exploit by virtue of stopping everything.
with that in mind the actual code looks like this:
> CPU0 CPU1
>
>
> lock inc %[val]; # 0x7fffffff
> jo 2f
>1: ...
>
> lock dec %[val]; # 0x80000000
> jo 2f
> 1: ...
>
>
>
>
>2: mov $0x7fffffff, %[val]
panic()
> jmp 1b
>
> 2: mov $0x80000000, %[val]
panic()
> jmp 1b
>
... and we never get this far.
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