On Friday, May 20, 2016 02:59:30 PM Kees Cook wrote: > On Fri, May 20, 2016 at 2:46 PM, Rafael J. Wysocki <raf...@kernel.org> wrote: > > On Fri, May 20, 2016 at 3:56 PM, Stephen Smalley <s...@tycho.nsa.gov> wrote: > >> On 05/20/2016 07:34 AM, Rafael J. Wysocki wrote: > >>> On Fri, May 20, 2016 at 9:15 AM, Ingo Molnar <mi...@kernel.org> wrote: > >>>> > >>>> * Logan Gunthorpe <log...@deltatee.com> wrote: > >>>> > >>>>> Hi, > >>>>> > >>>>> I have been working on a bug that causes my laptop to freeze during > >>>>> resume from hibernation. I did a bisect to find the offending commit: > >>>>> > >>>>> [ab76f7b4ab] x86/mm: Set NX on gap between __ex_table and rodata > >>>>> > >>>>> There is more information in the bugzilla report [1] that > >>>>> I've been working on but I will summarize things below. > >>>>> > >>>>> I've experienced intermittent but reproducible freezes when resuming > >>>>> from hibernation since about kernel version 3.19. The freeze was > >>>>> significantly more reproducible when a few applications were loaded > >>>>> before hibernation and would largely not happen if hibernated > >>>>> immediately after booting to a desktop. I did some tracing work to find > >>>>> that the kernel gets as far as the resume_image call in > >>>>> swsusp_arch_resume and I could not find any response from the image > >>>>> kernel when I hit the bug. I also did testing that seemed to rule out > >>>>> this being caused by a problematic driver. > >>>>> > >>>>> I did a successful bisect between 3.18 and 3.19 which found a bug in > >>>>> commit f5b2831d6 that was then later fixed by commit 55696b1f66 in 4.4. > >>>>> Then, I did a second bisect with a ported version of the fix to the > >>>>> first bug and found commit ab76f7b4ab in 4.3 to also break hibernation > >>>>> with what appears to be the exact same symptoms. Reverting that commit > >>>>> in recent kernels up to and including 4.6 fixes the issue and restores > >>>>> reliable hibernation. However, it's not at all clear to me why that > >>>>> commit would cause this issue or how to fix the issue without reverting. > >>>> > >>>> I've attached that commit below and also Cc:-ed a few more people who > >>>> might have > >>>> an idea about why this regressed. Worst-case we'll have to revert it. > >>> > >>> Without looking deep into mm, my theory would be that after this patch > >>> the final jump from the boot kernel to the image kernel's trampoline > >>> code during resume may crash the kernel if the trampoline page turns > >>> out to be NX in the boot kernel (it has to be executable in both the > >>> boot and the image kernels). > >> > >> So, pardon my ignorance, but where is this trampoline page placed in > >> kernel memory? > > > > On 32-bit its location has to be the same in both the boot and the > > image kernels and that's within kernel text in both cases, so that > > shouldn't be a problem. > > > > On 64-bit its location depends on the image kernel and specifically on > > the location of the restore_registers routine in it. The (virtual) > > address of that routine is stored in the restore_jump_address > > variable, so the page containing it (the trampoline page) can be found > > with the help of that. > > > > swsusp_arch_resume() sets up a temporary kernel mapping to finalize > > the image restoration and that page must not be NX in that mapping for > > things to work. > > It looks like nothing in the swsusp_arch_resume() -> get_safe_page() > -> get_image_page() path sets the page executable... > > Untested, but I wonder if this work work in swsusp_arch_resume() > before the memcpy? > > (apologies for any gmail-based whitespace mangling...) > > diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c > index 009947d419a6..c2f3ecc45bd4 100644 > --- a/arch/x86/power/hibernate_64.c > +++ b/arch/x86/power/hibernate_64.c > @@ -12,6 +12,7 @@ > #include <linux/smp.h> > #include <linux/suspend.h> > > +#include <asm/cacheflush.h> > #include <asm/init.h> > #include <asm/proto.h> > #include <asm/page.h> > @@ -89,6 +90,7 @@ int swsusp_arch_resume(void) > relocated_restore_code = (void *)get_safe_page(GFP_ATOMIC); > if (!relocated_restore_code) > return -ENOMEM; > + set_memory_x((unsigned long)relocated_restore_code, 1); > memcpy(relocated_restore_code, &core_restore_code, > &restore_registers - &core_restore_code); > >
We may not be on the right track with this I'm afraid. When the temporary kernel mapping is set up in swsusp_arch_resume(), it passes __PAGE_KERNEL_LARGE_EXEC as pmd_flag in the x86_mapping_info, so all memory should be executable after we switch to that which happens right at the beginning of restore_image(). So restore_image() and the code it jumps to should be fine from the executability perspective (including the final jump to restore_jump_address). Or am I missingy anything? Thanks, Rafael
