On Tue, Jun 23, 2020 at 04:59:14PM +0200, Joerg Roedel wrote:

On Tue, Jun 23, 2020 at 04:53:44PM +0200, Peter Zijlstra wrote:

quoted

+noinstr void idtentry_validate_ist(struct pt_regs *regs)
+{
+	if ((regs->sp & ~(EXCEPTION_STKSZ-1)) ==
+	    (_RET_IP_ & ~(EXCEPTION_STKSZ-1)))
+		die("IST stack recursion", regs, 0);
+}

Yes, this is a start, it doesn't cover the case where the NMI stack is
in-between, so I think you need to walk down regs->sp too.

That shouldn't be possible with the current code, I think.

The dumpstack code already has some logic for this.

Reliability of that depends on the unwinder, I wouldn't want the guess
uwinder to OOPS me by accident.