On Mon, Jun 27, 2016 at 10:28 AM, Linus Torvalds <[email protected]> wrote: > On Mon, Jun 27, 2016 at 8:54 AM, Andy Lutomirski <[email protected]> wrote: >> >> How about: >> >> tsk_stack = (unsigned long)task_stack_page(tsk); >> if (regs->rsp <= tsk_stack + 7*8 && regs->rsp > tsk_stack - PAGE_SIZE) { > > I'm not at all convinced that regs->rsp will be all that reliable > under a double-fault scenario either. I'd be more inclined to trusr > cr2 than the register state. > > It's true that double faults can happen for *other* reasons entirely, > and as such it's not clear that %cr2 is reliable either, but since > this is all just about a printout, I'd rather go that way anyway.
Fair enough. The chance that we get #GP-in-#GP or similar while CR2 coincidentally points to the guard page is quite low. I'll add all the details to the comment but I'll leave the code alone. FWIW, the manual only says that CS and RIP are untrustworthy, not that RSP is untrustworthy, but it doesn't specify *what* RSP would contain anywhere I can find. I don't think this is important enough to start harassing the Intel and AMD folks over. --Andy
