linux-kernel - Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

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: <13212319.WrhLzgRA6Z@wuerfel>
Date:	Tue, 21 Jun 2016 11:24:18 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

On Monday, June 20, 2016 4:43:30 PM CEST Andy Lutomirski wrote:
> 
> On my laptop, this adds about 1.5µs of overhead to task creation,
> which seems to be mainly caused by vmalloc inefficiently allocating
> individual pages even when a higher-order page is available on the
> freelist.

Would it help to have a fixed virtual address for the stack instead
and map the current stack to that during a task switch, similar to
how we handle fixmap pages?

That would of course trade the allocation overhead for a task switch
overhead, which may be better or worse. It would also give "current"
a constant address, which may give a small performance advantage
but may also introduce a new attack vector unless we randomize it
again.

	Arnd