On Mon, 09 Mar 2015 13:43:21 -0700 Dave Hansen <[email protected]> wrote:
> > From: Dave Hansen <[email protected]> > > Physical addresses are sensitive information. There are > existing, known exploits that are made easier if physical > information is available. Here is one example: > > http://www.cs.columbia.edu/~vpk/papers/ret2dir.sec14.pdf > > If you know the physical address of something you also know at > which kernel virtual address you can find something (modulo > highmem). It means that things that keep the kernel from > accessing user mappings (like SMAP/SMEP) can be worked around > because the _kernel_ mapping can get used instead. > > But, /proc/$pid/pagemap exposes the physical addresses of all > pages accessible to userspace. This works against all of the > efforts to keep kernel addresses out of places where unprivileged > apps can find them. > > This patch introduces a "paranoid" option for /proc. It can be > enabled like this: > > mount -o remount,paranoid /proc > > Or when /proc is mounted initially. When 'paranoid' mode is > active, opens to /proc/$pid/pagemap will return -EPERM for users > without CAP_SYS_RAWIO. It can be disabled like this: > > mount -o remount,notparanoid /proc > > The option is applied to the pid namespace, so an app that wanted > a separate policy from the rest of the system could get run in > its own pid namespace. > > I'm not really that stuck on the name. I'm not opposed to making > it apply only to pagemap or to giving it a pagemap-specific > name. Do we really need to disable pagemap entirely? What happens if we just obscure the addresses (ie: zero them)? > pagemap is also the kind of feature that could be used to escalate > privileged from root in to the kernel. It probably needs to be > protected in the same way that /dev/mem or module loading is in > cases where the kernel needs to be protected from root, thus the > choice to use CAP_SYS_RAWIO. Confused. If you have root, you can do mount -o notparanoid. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
