valgrind partially broken by current hardy-proposed kernel?

Kees Cook kees at
Mon Jun 2 22:01:20 UTC 2008

On Mon, Jun 02, 2008 at 09:34:51PM +0100, Colin Watson wrote:
> On Mon, Jun 02, 2008 at 09:56:13AM -0700, Kees Cook wrote:
> > That change was made for the release kernel, so you should see it with
> > -16 too.  Blocking NULL is a feature.  :)

Just so we're working on a single variable, does -16 show the behavior?

> > Why is ssh-add trying to allocate memory at 0x0?
> It's not. If anything in userspace is doing that it's valgrind (or
> possibly ld-linux itself, but it doesn't show up in an strace of ssh-add
> alone).

How very strange.  You can easily disable it -- it's just a sysctl

# protect bottom 64k of memory from mmap to prevent NULL-dereference
# attacks against potential future kernel security vulnerabilities.
# (Added in kernel 2.6.23.)
vm.mmap_min_addr = 65536

Just set that to 0 and you should have it back.


Kees Cook
Ubuntu Security Team

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