On Wed, Jun 15, 2016 at 10:23 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Wed, Jun 15, 2016 at 10:05 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> On Tue, Jun 14, 2016 at 11:01 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >>> Hi all- >>> >>> If you want to play with virtually mapped stacks, I have it more or >>> less working on x86 in a branch here: >>> >>> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/vmap_stack >>> >>> The core bit (virtually map the stack and fix the accounting) is just >>> a config option, but it needs the arch to opt-in. I suspect that >>> every arch will have its own set of silly issues to address to make it >>> work well. For x86, the silly issues are getting the OOPS to work >>> right and handling some vmalloc_fault oddities to avoid panicing at >>> random. >> >> Awesome! Some notes/questions: >> >> - there are a number of typos in commit messages and comments, just FYI > > Not surprising. I'll try to find and fix them. x86/cpa: In populate_pgd, don't set the pgd entry until it's populated: "anyther CPU propages" x86/cpa: Warn if kernel_unmap_pages_in_pgd is used inappropriately: "kenrnel entries" There was another repeated word, but I can't find it now. :P >> >> - where is the guard page added? I don't see anything leaving a hole at the end? > > Magic! The vmap code does this for us. Heh, can you point me to where? Does it have guards at both ends? >> - where is thread_info? I understand there to be two benefits from >> vmalloc stack: 1) thread_info can live elsewhere, 2) guard page can >> exist easily > > I think that thread_info is a separate issue except insofar as it's > needed for full exploit protection. Moving / eliminating it has > nothing to do with where the stack lives AFAIK. I'll get to it. Okay, cool. > I suspect that the hardest part will be eliminating the (mostly > pointless) thread_info::task field. IIUC, grsecurity puts a thread_info pointer in the percpu area, if that's any help. >> - this seems like it should Oops not warn: >> WARN_ON_ONCE(vm->nr_pages != THREAD_SIZE / PAGE_SIZE); >> that being wrong seems like a very bad state to continue from > > I'll change that. > >> >> - bikeshed: I think the CONFIG should live in arch/Kconfig (with a >> description of what an arch needs to support for it) and be called >> HAVE_ARCH_VMAP_STACK so that archs can select it instead of having >> multiple definitions of CONFIG_VMAP_STACK in each arch. > > I'll change that, too. Awesome! :) -Kees -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>