On Wed, Mar 18, 2015 at 5:11 PM, Dave Hansen <[email protected]> wrote: > On 03/18/2015 01:30 AM, Konstantin Khlebnikov wrote: >> + /* >> + * Read-only SUID/SGID binares are mapped as copy-on-read >> + * this protects them against exploiting with Rowhammer. >> + */ >> + if (!(file->f_mode & FMODE_WRITE) && >> + ((inode->i_mode & S_ISUID) || ((inode->i_mode & S_ISGID) && >> + (inode->i_mode & S_IXGRP)))) { >> + vm_flags &= ~(VM_SHARED | VM_MAYSHARE); >> + vm_flags |= VM_COR; >> + } > > I think we probably need to come to _some_ sort of understanding in the > kernel of how much we are willing to do to thwart these kinds of > attacks. I suspect it's a very deep rabbit hole. > > For this particular case, I don't see how this would be effective. The > existing exploit which you reference attacks PTE pages which are > unmapped in to the user address space. I'm confused how avoiding > mapping a page in to an attacker's process can keep it from being exploited. > > Right now, there's a relatively small number of pages that will get > COW'd for a SUID binary. This greatly increases the number which could > allow spraying of these (valuable) copy-on-read pages.
Yeah, on second thought that copy-on-read gives the same security level as hiding pfns from userspace. Sorry for the noise. It seems the only option is memory zoning: kernel should allocate all normal memory for userspace from isolated area which is kept far far away from important data. -- 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/
