On Mon, Dec 14, 2015 at 3:37 PM, Dave Hansen <dave@xxxxxxxx> wrote: > On 12/14/2015 12:05 PM, Kees Cook wrote: >> On Mon, Dec 14, 2015 at 11:06 AM, Dave Hansen <dave@xxxxxxxx> wrote: >>> > From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> >>> > Protection keys provide new page-based protection in hardware. >>> > But, they have an interesting attribute: they only affect data >>> > accesses and never affect instruction fetches. That means that >>> > if we set up some memory which is set as "access-disabled" via >>> > protection keys, we can still execute from it. > ... >>> > I haven't found any userspace that does this today. >> To realistically take advantage of this, it sounds like the linker >> would need to know to keep bss and data page-aligned away from text, >> and then set text to PROT_EXEC only? >> >> Do you have any example linker scripts for this? > > Nope. My linker-fu is weak. > > Can we even depend on the linker by itself? Even if the sections were > marked --x, we can't actually use them with those permissions unless we > have protection keys. > > Do we need some special tag on the section to tell the linker to map it > as --x under some conditions and r-x for others? Yeah, dunno. I was curious to see this working on a real example first, and then we could figure out how the linker should behave generally. Sounds like we need some kind of ELF flag to say "please use unreadable-exec memory mappings for this program, too. -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>