linux-kernel - Re: [PATCH] x86/refcount: Implement fast refcount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <58FF3273.5306.1C99E565@pageexec.freemail.hu>
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.