Messages in this thread | | | Date | Mon, 23 Jun 2008 07:04:35 -0700 | From | Arjan van de Ven <> | Subject | Re: mmap_min_addr/SECURITY_DEFAULT_MMAP_MIN_ADDR suggested values |
| |
On Mon, 23 Jun 2008 14:53:37 +0100 "Dr. David Alan Gilbert" <linux@treblig.org> wrote:
> Hi, > The config help for SECURITY_DEFAULT_MMAP_MIN_ADDR suggests 65536 > as a 'reasonable' value for x86 and the original mmap_min_addr > patches suggested that 'something like 64k' was a safe value that > wouldn't affect most programs. > > Where does this 64k value come from? A number of distros seem > to have followed this advice and have it set to 64k; but is there > really any likely benefit of having it larger than PAGE_SIZE say?
there's a few things in the kernel that are bigger than 4K (or rather, lead to pointers beyond 4K) so it's not all that bad advice.
> > I ask because I have an ancient program that maps stuff at 8k; the > general advice of stuff on the net seems to be to set this limit > to 0 if people have problems (I'm just lowering it to 4k), > but I was thinking perhaps using a lower default value would be more > secure since less people would take the easy answer and just turn the > feature off altogether.
interesting... what does the program do? (applications making assumptions on where they can mmap stuff... that's not really valid. Realistically, the only safe way to use MAP_FIXED is on memory that you got from mmap before.. think about it: what if glibc happened to mmap something there first?)
So I'm quite curious what/why this app is doing this
-- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org
| |