On Wed, Nov 22, 2017 at 05:19:14PM +0100, Pavel Machek wrote: > > This patch series implements something along the lines of KAISER for arm64: > > > > https://gruss.cc/files/kaiser.pdf > > > > although I wrote this from scratch because the paper has some funny > > assumptions about how the architecture works. There is a patch series > > in review for x86, which follows a similar approach: > > > > http://lkml.kernel.org/r/<[email protected]> > > > > and the topic was recently covered by LWN (currently subscriber-only): > > > > https://lwn.net/Articles/738975/ > > > > The basic idea is that transitions to and from userspace are proxied > > through a trampoline page which is mapped into a separate page table and > > can switch the full kernel mapping in and out on exception entry and > > exit respectively. This is a valuable defence against various KASLR and > > timing attacks, particularly as the trampoline page is at a fixed virtual > > address and therefore the kernel text can be randomized > > independently. > > If I'm willing to do timing attacks to defeat KASLR... what prevents > me from using CPU caches to do that?
Is that a rhetorical question? If not, then I'm probably not the best person to answer it. All I'm doing here is protecting against a class of attacks on kaslr that make use of the TLB/page-table walker to determine where the kernel is mapped. > There was blackhat talk about exactly that IIRC... Got a link? I'd be interested to see how the idea works in case there's an orthogonal defence against it. Will
