From: Borislav Petkov <bp@alien8.de>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "KP Singh" <kpsingh@kernel.org>,
"Dave Hansen" <dave.hansen@intel.com>,
"Josh Poimboeuf" <jpoimboe@kernel.org>,
linux-kernel@vger.kernel.org, pjt@google.com, evn@google.com,
tglx@linutronix.de, mingo@redhat.com,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
peterz@infradead.org, pawan.kumar.gupta@linux.intel.com,
kim.phillips@amd.com, alexandre.chartre@oracle.com,
daniel.sneddon@linux.intel.com,
"José Oliveira" <joseloliveira11@gmail.com>,
"Rodrigo Branco" <rodrigo@kernelhacking.com>,
"Alexandra Sandulescu" <aesa@google.com>,
"Jim Mattson" <jmattson@google.com>
Subject: Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2 protection with KERNEL_IBRS
Date: Tue, 21 Feb 2023 11:59:14 +0100 [thread overview]
Message-ID: <Y/SkAqvl8YCZXAnB@zn.tnic> (raw)
In-Reply-To: <50231372-2d6d-e4af-be88-5fe45e0c210d@citrix.com>
On Mon, Feb 20, 2023 at 11:30:46PM +0000, Andrew Cooper wrote:
> 1) Intel's legacy IBRS
> 2) AMD's regular IBRS
Yeah, we don't do that in the kernel.
> 3) AMD's AutoIBRS
>
> which all have different relevant behaviours for userspace. Just so
> it's written out coherently in at least one place...
>
> When SEV-SNP is enabled in firmware, whether or not it's being used by
> software, AutoIBRS keeps indirect predictions inhibited in all of
> ASID0. That's all host userspace to the non-hypervisor devs reading
> this thread.
Yap.
> For any AMD configuration setting STIBP, there must be an IBPB after
> having set STIBP. Setting STIBP alone does not evict previously
> created shared predictions. This one can go subtly wrong for anyone who
> assumes that Intel STIBP and AMD STIBP have the same behaviour.
We will IBPB eventually... on the next context switch.
> Furthermore, extra care needs taking on vmexit because transitioning
> from the guest STIBP setting to the host STIBP setting can leave shared
> predictions intact.
From what I can tell from looking at the SVM code, we don't do anything
special there when restoring SPEC_CTRL.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2023-02-21 10:59 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-20 12:01 [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2 protection with KERNEL_IBRS KP Singh
2023-02-20 12:13 ` Josh Poimboeuf
2023-02-20 12:20 ` KP Singh
2023-02-20 12:34 ` KP Singh
2023-02-20 14:31 ` Borislav Petkov
2023-02-20 15:38 ` Dave Hansen
2023-02-20 19:57 ` Andrew Cooper
2023-02-20 21:10 ` Borislav Petkov
2023-02-20 23:01 ` KP Singh
2023-02-20 23:30 ` Andrew Cooper
2023-02-20 23:45 ` KP Singh
2023-02-21 18:52 ` KP Singh
2023-02-21 10:59 ` Borislav Petkov [this message]
2023-02-20 16:34 ` Josh Poimboeuf
2023-02-20 17:46 ` Borislav Petkov
2023-02-20 17:59 ` Josh Poimboeuf
2023-02-20 18:01 ` KP Singh
2023-02-20 18:22 ` Borislav Petkov
2023-02-20 18:44 ` KP Singh
2023-02-20 18:51 ` Borislav Petkov
2023-02-20 18:56 ` KP Singh
2023-02-20 19:02 ` Borislav Petkov
2023-02-20 19:10 ` KP Singh
2023-02-20 18:27 ` [PATCH] x86/bugs: Allow STIBP with IBRS Josh Poimboeuf
2023-02-20 18:28 ` kernel test robot
2023-02-20 18:33 ` KP Singh
2023-02-20 18:59 ` Josh Poimboeuf
2023-02-20 19:04 ` KP Singh
2023-02-20 19:19 ` Josh Poimboeuf
2023-02-20 18:34 ` Borislav Petkov
2023-02-20 19:09 ` Josh Poimboeuf
2023-02-20 19:16 ` KP Singh
2023-02-20 19:35 ` Josh Poimboeuf
2023-02-20 19:38 ` KP Singh
2023-02-20 19:20 ` Borislav Petkov
2023-02-22 1:20 ` Pawan Gupta
2023-02-22 1:26 ` KP Singh
2023-02-22 1:38 ` Pawan Gupta
2023-02-27 19:59 ` [tip: x86/urgent] x86/speculation: Allow enabling STIBP with legacy IBRS tip-bot2 for KP Singh
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