linux-kernel - vmalloced stacks on x86

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-next>] [day] [month] [year] [list]

Date:	Fri, 24 Oct 2014 17:22:31 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: vmalloced stacks on x86_64?

Is there any good reason not to use vmalloc for x86_64 stacks?

The tricky bits I've thought of are:

 - On any context switch, we probably need to probe the new stack
before switching to it.  That way, if it's going to fault due to an
out-of-sync pgd, we still have a stack available to handle the fault.

 - Any time we change cr3, we may need to check that the pgd
corresponding to rsp is there.  If now, we need to sync it over.

 - For simplicity, we probably want all stack ptes to be present all
the time.  This is fine; vmalloc already works that way.

 - If we overrun the stack, we double-fault.  This should be easy to
detect: any double-fault where rsp is less than 20 bytes from the
bottom of the stack is a failure to deliver a non-IST exception due to
 a stack overflow.  The question is: what do we do if this happens?
We could just panic (guaranteed to work).  We could also try to
recover by killing the offending task, but that might be a bit
challenging, since we're in IST context.  We could do something truly
awful: increment RSP by a few hundred bytes, point RIP at do_exit, and
return from the double fault.

Thoughts?  This shouldn't be all that much code.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/