On Tue, Jun 21, 2016 at 12:44 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Tuesday, June 21, 2016 2:32:28 PM CEST Rik van Riel wrote: >> On Tue, 2016-06-21 at 10:13 -0700, Kees Cook wrote: >> > On Tue, Jun 21, 2016 at 9:59 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx >> > > wrote: >> > > >> > > I'm tempted to explicitly disallow VM_NO_GUARD in the vmalloc >> > > range. >> > > It has no in-tree users for non-fixed addresses right now. >> > What about the lack of pre-range guard page? That seems like a >> > critical feature for this. >> >> If VM_NO_GUARD is disallowed, and every vmalloc area has >> a guard area behind it, then every subsequent vmalloc area >> will have a guard page ahead of it. >> >> I think disallowing VM_NO_GUARD will be all that is required. >> >> The only thing we may want to verify on the architectures that >> we care about is that there is nothing mapped immediately before >> the start of the vmalloc range, otherwise the first vmalloced >> area will not have a guard page below it. > > FWIW, ARM has an 8MB guard area between the linear mapping of > physical memory and the start of the vmalloc area. I have not > checked any of the other architectures though. If we start banning VM_NO_GUARD in the vmalloc area, we could also explicitly prevent use of the bottom page of the vmalloc area. > > Arnd -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
