On 04/28/17 at 08:25am, Ingo Molnar wrote: > > * Baoquan He <b...@redhat.com> wrote: > > > Dave found kdump kernel with kaslr enabled will reset to bios immediately > > if physical randomization failed to find a new position for kernel. But > > kernel with 'nokaslr' option works in this case. > > > > The reason is kaslr will install a new page table for ident mapping, > > while it missed to consider building ident mapping for original area > > of kernel if kaslr failed on physical randomization. > > > > This only happens in kexec/kdump kernel. Since ident mapping has been > > built for kexec/kdump in 1st kernel for the whole memory by calling > > init_pgtable(). Here if physical randomizaiton failed, it won't build > > ident mapping for the original area of kernel but change to new page > > table '_pgtable'. Then kernel will reset to bios immediately caused by > > no ident mapping. > > > > While normal kernel won't be impacted because it comes here via > > startup_32() and cr3 will be _pgtable already. In startup_32() ident > > mapping is built for 0~4G area. In kaslr We just append to the existing > > area instead of entirely overwriting it for on-demand ident mapping > > building. So ident mapping for the original area of kernel is still > > there. > > > > So for fixing it, We just switch to the new ident mapping page table > > when physical kaslr succeeds. Otherwise we keep the old page table > > unchanged just like nokaslr does. > > > > Signed-off-by: Baoquan He <b...@redhat.com> > > Signed-off-by: Dave Young <dyo...@redhat.com> > > Acked-by: Kees Cook <keesc...@chromium.org> > > That's not a valid signoff chain. I made it: > > Reported-by: Dave Young <dyo...@redhat.com> > Signed-off-by: Baoquan He <b...@redhat.com> > Acked-by: Dave Young <dyo...@redhat.com> > Acked-by: Kees Cook <keesc...@chromium.org> > > (Let me know if that's not the proper authorship chain.)
Yeah, this is fine, thanks. Next time I will notice this.
