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From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	pawan.kumar.gupta@linux.intel.com,
	antonio.gomez.iglesias@linux.intel.com,
	"H. Peter Anvin" <hpa@zytor.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/speculation: Add BHI_DIS support
Date: Thu, 14 Jul 2022 22:04:20 +0200	[thread overview]
Message-ID: <YtB2xJdsOHSJV7Py@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220714195236.9311-1-daniel.sneddon@linux.intel.com>

On Thu, Jul 14, 2022 at 12:52:35PM -0700, Daniel Sneddon wrote:
> Branch History Injection (BHI) attacks can be mitigated using the
> BHI_DIS_S indirect predictor control bit located in MSR_IA32_SPEC_CTRL
> register. Set BHI_DIS in MSR_IA32_SPC_CTRL to prevent predicted
> targets of indirect branches executed in CPL0, CPL1, or CPL2 from
> being selected based on branch history from branches executed in CPL3.
> Support for this feature is enumerated by CPUID.7.2.EDX[BHI_CTRL] (bit 4).

What actual hardware will have this?

> Users wanting BHI protection can specify spectre_v2=eibrs,bhi_dis to
> enable hardware BHI protections.  On platforms where BHI protections
> are not available in the hardware revert to eibrs,retpoline
> mitigations.

AFAICT this doesn't get auto-selected; how bad is performance for this
to not be so?

      parent reply	other threads:[~2022-07-14 20:04 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-14 19:52 [PATCH] x86/speculation: Add BHI_DIS support Daniel Sneddon
2022-07-14 19:58 ` Boris Petkov
2022-07-14 20:04 ` Peter Zijlstra [this message]

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