On Fri, Mar 16, 2018 at 10:22:29AM -0700, Linus Torvalds wrote: > On Fri, Mar 16, 2018 at 4:48 AM, Borislav Petkov <[email protected]> wrote: > > On Thu, Mar 15, 2018 at 02:01:32PM -0500, Josh Poimboeuf wrote: > >> no_context() has the following line, right before it calls oops_end(): > >> > >> /* Executive summary in case the body of the oops scrolled away */ > >> printk(KERN_DEFAULT "CR2: %016lx\n", address); > >> > >> I think that line can now be removed, since the executive summary > >> __show_regs() will include CR2. > > > > Good idea. Done. > > NOOOO! > > Guys, %cr2 CAN AND DOES CHANGE! > > The reason we do that > > printk(KERN_DEFAULT "CR2: %016lx\n", address); > > is because WE ARE NOT PRINTING OUT THE CURRENT CR2 REGISTER!
Good point. I missed the fact that no_context() isn't printing the current CR2. > This is really damn important. > > The "address" register contains the CR2 value as it was read *very* > early in the page fault case, before we enabled interrupts, and before > we did various random things that can cause further page faults and > change CR2! > > So the executive summary that does __show_regs() may end up showing > something completely different than the actual faulting address, > because we might have taken a vmalloc-space exception in the meantime, > for example. > > Do *NOT* get rid of that thing. > > You're better off getting rid of the CR2 line from __show_regs(), > because it can be dangerously confusing. It's not actually part of the > saved register state at all, it's something entirely different. It's > like showing the current eflags rather than the eflags saved on the > faulting stack. True, it's probably best to remove it. The only time we need CR2's value is presumably when it would have already been printed in no_context(), and so it primarily just adds confusion as you said. -- Josh
