On 2018/1/6 15:55, Dave Hansen wrote: > On 01/05/2018 10:53 PM, Hanjun Guo wrote: >>> + /* >>> + * PTI poisons low addresses in the kernel page tables in the >>> + * name of making them unusable for userspace. To execute >>> + * code at such a low address, the poison must be cleared. >>> + */ >>> + pgd->pgd &= ~_PAGE_NX; >>> >>> We will have a try in a minute, and report back later. >> And it works，we can boot/reboot the system successfully, thank >> you all the quick response and debug! > I think I'll just submit the attached patch if there are no objections > (and if it works, of course!).
We tested that placing the NX clearing after pud_alloc(), and it works, patch below should work as well. > > I just stuck the NX clearing at the bottom. > > > pti-tboot-fix.patch > > > From: Dave Hansen <dave.han...@linux.intel.com> > > This is another case similar to what EFI does: create a new set of > page tables, map some code at a low address, and jump to it. PTI > mistakes this low address for userspace and mistakenly marks it > non-executable in an effort to make it unusable for userspace. Undo > the poison to allow execution. > > Signed-off-by: Dave Hansen <dave.han...@linux.intel.com> > Cc: Ning Sun <ning....@intel.com> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: "H. Peter Anvin" <h...@zytor.com> > Cc: x...@kernel.org > Cc: tboot-de...@lists.sourceforge.net > Cc: linux-kernel@vger.kernel.org > --- > > b/arch/x86/kernel/tboot.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff -puN arch/x86/kernel/tboot.c~pti-tboot-fix arch/x86/kernel/tboot.c > --- a/arch/x86/kernel/tboot.c~pti-tboot-fix 2018-01-05 21:50:55.755554960 > -0800 > +++ b/arch/x86/kernel/tboot.c 2018-01-05 23:51:41.368536890 -0800 > @@ -138,6 +138,17 @@ static int map_tboot_page(unsigned long > return -1; > set_pte_at(&tboot_mm, vaddr, pte, pfn_pte(pfn, prot)); > pte_unmap(pte); > + > + /* > + * PTI poisons low addresses in the kernel page tables in the > + * name of making them unusable for userspace. To execute > + * code at such a low address, the poison must be cleared. > + * > + * Note: 'pgd' actually gets set in p4d_alloc() _or_ > + * pud_alloc() depending on 4/5-level paging. > + */ > + pgd->pgd &= ~_PAGE_NX; > + > return 0; > } Thanks Hanjun
