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Message-ID: <20200623152326.GL4817@hirez.programming.kicks-ass.net>
Date: Tue, 23 Jun 2020 17:23:26 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Joerg Roedel <jroedel@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>, Joerg Roedel <joro@...tes.org>,
Dave Hansen <dave.hansen@...el.com>,
Tom Lendacky <Thomas.Lendacky@....com>,
Mike Stunes <mstunes@...are.com>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, Juergen Gross <JGross@...e.com>,
Jiri Slaby <jslaby@...e.cz>, Kees Cook <keescook@...omium.org>,
kvm list <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Hellstrom <thellstrom@...are.com>,
Linux Virtualization <virtualization@...ts.linux-foundation.org>,
X86 ML <x86@...nel.org>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP
from userspace)
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:
> > +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.
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