Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 21 Jun 2016 10:27:18 -0700
From: Andy Lutomirski <>
To: Linus Torvalds <>
Cc: Andy Lutomirski <>, "the arch/x86 maintainers" <>, 
	Linux Kernel Mailing List <>, 
	"" <>, Borislav Petkov <>, 
	Nadav Amit <>, Kees Cook <>, 
	Brian Gerst <>, 
	"" <>, Josh Poimboeuf <>, 
	Jann Horn <>, Heiko Carstens <>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

On Tue, Jun 21, 2016 at 10:16 AM, Linus Torvalds
<> wrote:
> On Tue, Jun 21, 2016 at 9:45 AM, Andy Lutomirski <> wrote:
>> So I'm leaning toward fewer cache entries per cpu, maybe just one.
>> I'm all for making it a bit faster, but I think we should weigh that
>> against increasing memory usage too much and thus scaring away the
>> embedded folks.
> I don't think the embedded folks will be scared by a per-cpu cache, if
> it's just one or two entries.  And I really do think that even just
> one or two entries will indeed catch a lot of the cases.
> And yes, fork+execve() is too damn expensive in page table build-up
> and tear-down. I'm not sure why bash doesn't do vfork+exec for when it
> has to wait for the process anyway, but it doesn't seem to do that.

I don't know about bash, but glibc very recently fixed a long-standing
but in posix_spawn and started using clone() in a sensible manner for

FWIW, it may be a while before this can be enabled in distro kernels.
There are some code paths (*cough* crypto users *cough*) that think
that calling sg_init_one with a stack address is a reasonable thing to
do, and it doesn't work with a vmalloced stack.  grsecurity works
around this by using a real lowmem higher-order stack, aliasing it
into vmalloc space, and arranging for virt_to_phys to backtrack the
alias, but eww.  I think I'd rather find and fix the bugs, assuming
they're straightforward.


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.