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Date: Tue, 29 Mar 2016 17:34:00 -0600
From: Scotty Bauer <>
To: Linus Torvalds <>
Cc: Linux Kernel Mailing List <>,
 "" <>,
 the arch/x86 maintainers <>, Andi Kleen <>,
 Andy Lutomirski <>, Ingo Molnar <>,
 Thomas Gleixner <>,
Subject: Re: [PATCH v4 0/4] SROP Mitigation: Sigreturn Cookies

On 03/29/2016 05:25 PM, Linus Torvalds wrote:
> On Tue, Mar 29, 2016 at 6:11 PM, Scotty Bauer <> wrote:
>> Yeah I had toyed with using hashes, I used hash_64 not md5 which is like 14
>> extra instructions or something.
> That sounds fine. Anything that requires enough code to undo that it
> kind of defeats the purpose of a SROP should be enough. It's not about
> encryption, I'd just think that if you can force the buffer overflow
> while already in a signal handler, you'd want something that is at
> least *slightly* harder to defeat than a single "xor" instruction.
>> It's not hard to implement So I can try it. When you say an extra hardening
>> mode do you mean hide it behind a sysctl or some sort of compile time CONFIG?
> Since there already is a sysctl, I'd just assume that.
> The important part is that the *default* value for that sysctl can't
> break real applications. I don't really count CRIU as a real app, if
> only because once you start doing checkpoint-restore you are going to
> do some amount of system maintenance anyway, so somebody doing CRIU is
> kind of expected to have a certain amount of system expertise, I would
> say.
> But dosemu - or Wine - is very much something that "normal people" run
> - people who we do *not* expect to have to know about new sysctl's
> etc. They already have one (mmap at zero), but that is very directly
> related to what vm86 mode and Wine does, and people have had time to
> learn about it. Let's not add another.
> So testing dosemu and wine would be good. I wonder what else has shown
> issues with signal stack layout changes. Debuggers and some JIT
> engines, I suspect.
>               Linus

Alright I'll test Wine/Mono, Dosemu, some random languages/debuggers see if
there is anything that breaks.


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