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. > > This patch uses protection keys to set up mappings to do just that. > If a user calls: > > mmap(..., PROT_EXEC); > or > mprotect(ptr, sz, PROT_EXEC); > > (note PROT_EXEC-only without PROT_READ/WRITE), the kernel will > notice this, and set a special protection key on the memory. It > also sets the appropriate bits in the Protection Keys User Rights > (PKRU) register so that the memory becomes unreadable and > unwritable. > > 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? -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>