* Baoquan He <[email protected]> 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 <[email protected]> > Signed-off-by: Dave Young <[email protected]> > Acked-by: Kees Cook <[email protected]>
That's not a valid signoff chain. I made it: Reported-by: Dave Young <[email protected]> Signed-off-by: Baoquan He <[email protected]> Acked-by: Dave Young <[email protected]> Acked-by: Kees Cook <[email protected]> (Let me know if that's not the proper authorship chain.) Thanks, Ingo
