From: Jim Mattson <jmattson@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>,
Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH] KVM: nSVM: vmentry ignores EFER.LMA and possibly RFLAGS.VM
Date: Thu, 9 Jul 2020 11:28:25 -0700 [thread overview]
Message-ID: <CALMp9eRSvdx+UHggLbvFPms3Li2KY-RjZhjGjcQ3=GbSB1YyyA@mail.gmail.com> (raw)
In-Reply-To: <782fdf92-38f8-c081-9796-5344ab3050d5@redhat.com>
On Thu, Jul 9, 2020 at 10:25 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 09/07/20 19:12, Jim Mattson wrote:
> >> +
> >> + /* The processor ignores EFER.LMA, but svm_set_efer needs it. */
> >> + efer &= ~EFER_LMA;
> >> + if ((nested_vmcb->save.cr0 & X86_CR0_PG)
> >> + && (nested_vmcb->save.cr4 & X86_CR4_PAE)
> >> + && (efer & EFER_LME))
> >> + efer |= EFER_LMA;
> > The CR4.PAE check is unnecessary, isn't it? The combination CR0.PG=1,
> > EFER.LMA=1, and CR4.PAE=0 is not a legal processor state.
Oops, I meant EFER.LME above.
Krish pointed out that I was quoting from Intel's documentation. The
same constraints are covered in Table 14-5 of AMD's APM, volume 2.
> Yeah, I was being a bit cautious because this is the nested VMCB and it
> can be filled in with invalid state, but indeed that condition was added
> just yesterday by myself in nested_vmcb_checks (while reviewing Krish's
> CR0/CR3/CR4 reserved bit check series).
From Canonicalization and Consistency Checks of section 15.5 in AMD's
APM, volume 2:
The following conditions are considered illegal state combinations:
...
EFER.LME and CR0.PG are both set and CR4.PAE is zero.
This VMCB state should result in an immediate #VMEXIT with exit code -1.
> That said, the VMCB here is guest memory and it can change under our
> feet between nested_vmcb_checks and nested_prepare_vmcb_save. Copying
> the whole save area is overkill, but we probably should copy at least
> EFER/CR0/CR3/CR4 in a struct at the beginning of nested_svm_vmrun; this
> way there'd be no TOC/TOU issues between nested_vmcb_checks and
> nested_svm_vmrun. This would also make it easier to reuse the checks in
> svm_set_nested_state. Maybe Maxim can look at it while I'm on vacation,
> as he's eager to do more nSVM stuff. :D
I fear that nested SVM is rife with TOCTTOU issues.
next prev parent reply other threads:[~2020-07-09 18:28 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-09 9:55 [PATCH] KVM: nSVM: vmentry ignores EFER.LMA and possibly RFLAGS.VM Paolo Bonzini
2020-07-09 17:12 ` Jim Mattson
2020-07-09 17:25 ` Paolo Bonzini
2020-07-09 18:28 ` Jim Mattson [this message]
2020-07-09 18:31 ` Paolo Bonzini
2020-07-09 18:40 ` Jim Mattson
2020-07-09 18:41 ` Paolo Bonzini
2020-07-10 8:37 ` Maxim Levitsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CALMp9eRSvdx+UHggLbvFPms3Li2KY-RjZhjGjcQ3=GbSB1YyyA@mail.gmail.com' \
--to=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mlevitsk@redhat.com \
--cc=pbonzini@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).