From: Borislav Petkov <bp@alien8.de>
To: Sean Christopherson <seanjc@google.com>
Cc: Jane Malalane <jane.malalane@citrix.com>,
LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Pu Wen <puwen@hygon.cn>, Paolo Bonzini <pbonzini@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Yazen Ghannam <Yazen.Ghannam@amd.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Huang Rui <ray.huang@amd.com>, Andy Lutomirski <luto@kernel.org>,
Kim Phillips <kim.phillips@amd.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL
Date: Mon, 18 Oct 2021 21:37:07 +0200 [thread overview]
Message-ID: <YW3M40tOILjI3DiD@zn.tnic> (raw)
In-Reply-To: <YW3LJdztZom+xQHv@google.com>
On Mon, Oct 18, 2021 at 07:29:41PM +0000, Sean Christopherson wrote:
> This isn't correct. When running as a guest, the intended behavior is to fully
> trust the CPUID.0x80000021 bit.
Really? Because I'm coming from an SEV-SNP mail thread where we don't
trust the HV at all and we even hand in a CPUID page into the guest...
:-P
> If bit 6 is set, yay, the hypervisor has told the kernel that it
> will only ever run on hardware without the bug. If bit 6 is clear
> and HYPERVISOR is true, then the FMS crud can't be trusted because
> the kernel _may_ run on affected hardware in the future even if the
> current underlying hardware is not affected.
Ok, I see, then the CPUID check needs to go first, makes sense.
> I agree. If the argument for this patch is that the kernel can be migrated to
> older hardware, then it stands to reason that the kernel could also be migrated
> to a different CPU vendor entirely. E.g. start on Intel, migrate to Zen1, kaboom.
Migration across vendors? Really, that works?
I'll believe it only when I see it with my own eyes.
:-)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-10-18 19:37 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-13 14:22 [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL Jane Malalane
2021-10-13 16:46 ` Greg KH
2021-10-18 18:17 ` Borislav Petkov
2021-10-18 19:10 ` H. Peter Anvin
2021-10-18 19:31 ` Borislav Petkov
2021-10-18 19:29 ` Sean Christopherson
2021-10-18 19:37 ` Borislav Petkov [this message]
2021-10-18 20:05 ` Sean Christopherson
2021-10-18 20:18 ` Andrew Cooper
2021-10-18 20:06 ` Andrew Cooper
2021-10-18 21:46 ` Borislav Petkov
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