Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)

Joerg Roedel
2020-06-23T14:59:20Z

On Tue, Jun 23, 2020 at 04:53:44PM +0200, Peter Zijlstra wrote:
> +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. The dumpstack
code already has some logic for this.

Joerg