From: Andrew Cooper <andrew.cooper3@citrix.com>
To: David Woodhouse <dwmw2@infradead.org>,
Borislav Petkov <bp@alien8.de>,
KarimAllah Ahmed <karahmed@amazon.com>
Cc: <arjan@linux.intel.com>, <tglx@linutronix.de>,
<karahmed@amazon.de>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>, <tim.c.chen@linux.intel.com>,
<peterz@infradead.org>, <pbonzini@redhat.com>,
<ak@linux.intel.com>, <torvalds@linux-foundation.org>,
<gregkh@linux-foundation.org>
Subject: Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB
Date: Sun, 21 Jan 2018 19:37:14 +0000 [thread overview]
Message-ID: <f9141600-45e4-999a-e997-05eeb56cda29@citrix.com> (raw)
In-Reply-To: <1516563060.9814.52.camel@infradead.org>
On 21/01/18 19:31, David Woodhouse wrote:
> On Sun, 2018-01-21 at 20:01 +0100, Borislav Petkov wrote:
>> so execution runs directly into the MSR write and the JMP is gone.
>>
>> So I don't see indirect branches anywhere...
> Wait until the wind changes.
>
> Congratulations, you've just turned a potential GCC missed optimisation
> into a kernel bug. We don't *care* that it's unlikely that GCC will
> miss that optimisation. The point is that it doesn't *have* to do it,
> and we don't *check*.
>
> cf. https://lkml.org/lkml/2018/1/12/176
>
>
> ... after which Peter went off and implemented that check, which is all
> fine and dandy but let's not rely on backporting that too.
It doesn't matter if an attacker can use SP1 to try and skip the IBPB.
Exits to userspace/guest are serialising (with some retroactive updates
to the architecture spec coming), so an attacker can't cause victim code
to be executed before speculation has caught up and noticed that the
IBPB did need to happen.
~Andrew
next prev parent reply other threads:[~2018-01-21 19:37 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-21 9:49 [PATCH v2 0/8] Speculation Control feature support, IBPB David Woodhouse
2018-01-21 9:49 ` [PATCH v2 1/8] x86/cpufeatures: Add Intel feature bits for Speculation Control David Woodhouse
2018-01-21 10:17 ` Ingo Molnar
2018-01-21 9:49 ` [PATCH v2 2/8] x86/cpufeatures: Add AMD feature bits for Prediction Command David Woodhouse
2018-01-21 17:50 ` Tom Lendacky
2018-01-21 18:01 ` Andrew Cooper
2018-01-22 14:31 ` Tom Lendacky
2018-01-22 14:33 ` Andrew Cooper
2018-01-21 9:49 ` [PATCH v2 3/8] x86/msr: Add definitions for new speculation control MSRs David Woodhouse
2018-01-21 13:06 ` Jiri Slaby
2018-01-21 13:27 ` David Woodhouse
2018-01-21 9:49 ` [PATCH v2 4/8] x86/pti: Do not enable PTI on fixed Intel processors David Woodhouse
2018-01-21 13:38 ` Borislav Petkov
2018-01-21 9:49 ` [PATCH v2 5/8] x86/speculation: Add basic support for IBPB David Woodhouse
2018-01-21 10:26 ` Ingo Molnar
2018-01-21 18:06 ` Borislav Petkov
2018-01-21 18:29 ` KarimAllah Ahmed
2018-01-21 19:01 ` Borislav Petkov
2018-01-21 19:31 ` David Woodhouse
2018-01-21 19:37 ` Andrew Cooper [this message]
2018-01-21 20:04 ` David Woodhouse
2018-01-21 20:19 ` Andrew Cooper
2018-01-21 21:25 ` David Woodhouse
2018-01-21 19:53 ` Borislav Petkov
2018-01-21 18:54 ` David Woodhouse
2018-01-21 19:04 ` Borislav Petkov
2018-01-21 19:31 ` David Woodhouse
2018-01-21 19:54 ` Borislav Petkov
2018-01-21 20:07 ` David Woodhouse
2018-01-21 20:17 ` Borislav Petkov
2018-01-21 9:49 ` [PATCH v2 6/8] x86/kvm: Add IBPB support David Woodhouse
2018-01-21 18:06 ` Tom Lendacky
2018-01-21 9:49 ` [PATCH v2 7/8] x86/speculation: Use Indirect Branch Prediction Barrier in context switch David Woodhouse
2018-01-21 9:49 ` [PATCH v2 8/8] x86/mm: Only flush indirect branches when switching into non dumpable process David Woodhouse
2018-01-21 10:33 ` Ingo Molnar
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