Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Fri, 5 Apr 2019 07:14:11 -0600
From: Andy Lutomirski <>
To: "Reshetova, Elena" <>
Cc: Kees Cook <>, Andy Lutomirski <>,
 Kernel Hardening <>,
 Josh Poimboeuf <>, Jann Horn <>,
 "Perla, Enrico" <>, Ingo Molnar <>,
 Borislav Petkov <>, Thomas Gleixner <>,
 Peter Zijlstra <>,
 Greg KH <>
Subject: Re: [RFC PATCH] x86/entry/64: randomize kernel stack offset upon syscall

On Apr 5, 2019, at 4:14 AM, Reshetova, Elena <> wrote:

>> On Thu, Apr 4, 2019 at 4:41 AM Reshetova, Elena
>> <> wrote:
>>> What I still don't fully understand here (due to my little knowledge of
>>> compilers) and afraid of is that the asm code that alloca generates (see my version)
>>> and the alignment might differ on the different targets, etc.
>> I guess it's possible, but for x86_64, since appears to be consistent.
> So, yes, I double checked this now with just printing all possible offsets I get for rsp
> from do_syscall_64, it is indeed 33 different offsets, so it is indeed more like 5 bits of entropy. 
> We can increase it, if we want and people are ok with losing a bit more stack space. 
>>> If you tried it on yours, can you send me the asm code that it produced for you?
>>> Is it different from mine?
>> You can compare compiler outputs here. Here's gcc vs clang for this code:
>> You can adjust compiler versions, etc.
> Oh, this is handy! Thank you for the link! 
> So, should I resend to lkml (with some cosmetic fixes) or how to proceed with this?
> I will also update the randomness bit info. 

Go ahead and send a new version, please.

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.