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Date:   Thu, 14 Jul 2022 19:58:08 +0000
From:   Boris Petkov <bp@alien8.de>
To:     Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org
CC:     pawan.kumar.gupta@linux.intel.com,
        antonio.gomez.iglesias@linux.intel.com, linux-doc@vger.kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/speculation: Add BHI_DIS support
In-Reply-To: <20220714195236.9311-1-daniel.sneddon@linux.intel.com>
References: <20220714195236.9311-1-daniel.sneddon@linux.intel.com>
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On July 14, 2022 7:52:35 PM UTC, Daniel Sneddon <daniel=2Esneddon@linux=2Ei=
ntel=2Ecom> 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=2E 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=2E
>Support for this feature is enumerated by CPUID=2E7=2E2=2EEDX[BHI_CTRL] (=
bit 4)=2E
>
>Users wanting BHI protection can specify spectre_v2=3Deibrs,bhi_dis to
>enable hardware BHI protections=2E  On platforms where BHI protections
>are not available in the hardware revert to eibrs,retpoline
>mitigations=2E

Why is this a separately selectable option and not automatically enabled?

--=20
Sent from a small device: formatting sux and brevity is inevitable=2E