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. > > - 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. > > - 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. I suspect that the hardest part will be eliminating the (mostly pointless) thread_info::task field. > > - 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. > > Thanks for digging into this! > > -Kees > > -- > Kees Cook > Chrome OS & Brillo Security -- Andy Lutomirski AMA Capital Management, LLC -- 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>