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From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Benjamin Gray" <bgray@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>
Cc: linux-hardening@vger.kernel.org, ajd@linux.ibm.com,
	cmr@bluescreens.de, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override
Date: Tue, 07 Mar 2023 15:30:39 +1000	[thread overview]
Message-ID: <CQZWKF2U2GVM.1X6AAD3SM05D6@bobo> (raw)
In-Reply-To: <20221128024458.46121-8-bgray@linux.ibm.com>

On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:
> The DEXCR Speculative Branch Hint Enable (SBHE) aspect controls whether
> the hints provided by BO field of Branch instructions are obeyed during
> speculative execution.
>
> SBHE behaviour per ISA 3.1B:
>
> 0:	The hints provided by BO field of Branch instructions may be
> 	ignored during speculative execution
>
> 1:	The hints provided by BO field of Branch instructions are obeyed
> 	during speculative execution
>
> Add a sysctl entry to allow changing this aspect globally in the system
> at runtime:
>
> 	/proc/sys/kernel/speculative_branch_hint_enable
>
> Three values are supported:
>
> -1:	Disable DEXCR SBHE sysctl override
>  0:	Override and set DEXCR[SBHE] aspect to 0
>  1:	Override and set DEXCR[SBHE] aspect to 1
>
> Internally, introduces a mechanism to apply arbitrary system wide
> overrides on top of the prctl() config.

Why have an override for this, and not others?

Thanks,
Nick


  reply	other threads:[~2023-03-07  5:31 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-28  2:44 [RFC PATCH 00/13] Add DEXCR support Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 01/13] powerpc/book3s: Add missing <linux/sched.h> include Benjamin Gray
2023-03-07  4:28   ` Nicholas Piggin
2022-11-28  2:44 ` [RFC PATCH 02/13] powerpc: Add initial Dynamic Execution Control Register (DEXCR) support Benjamin Gray
2023-03-07  4:45   ` Nicholas Piggin
2023-03-09 23:46     ` Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 03/13] powerpc/dexcr: Handle hashchk exception Benjamin Gray
2022-11-29 10:39   ` Nicholas Piggin
2022-11-29 22:04     ` Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 04/13] powerpc/dexcr: Support userspace ROP protection Benjamin Gray
2023-03-07  5:05   ` Nicholas Piggin
2023-03-07  5:37     ` Benjamin Gray
2023-03-21  4:51       ` Nicholas Piggin
2022-11-28  2:44 ` [RFC PATCH 05/13] prctl: Define PowerPC DEXCR interface Benjamin Gray
2023-03-07  5:07   ` Nicholas Piggin
2022-11-28  2:44 ` [RFC PATCH 06/13] powerpc/dexcr: Add prctl implementation Benjamin Gray
2023-03-07  5:12   ` Nicholas Piggin
2022-11-28  2:44 ` [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override Benjamin Gray
2023-03-07  5:30   ` Nicholas Piggin [this message]
2023-03-07  5:58     ` Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 08/13] powerpc/dexcr: Add enforced userspace ROP protection config Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 09/13] selftests/powerpc: Add more utility macros Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 10/13] selftests/powerpc: Add hashst/hashchk test Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 11/13] selftests/powerpc: Add DEXCR prctl, sysctl interface test Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 12/13] selftests/powerpc: Add DEXCR status utility lsdexcr Benjamin Gray
2022-11-28  2:44 ` [RFC PATCH 13/13] Documentation: Document PowerPC kernel DEXCR interface Benjamin Gray
2023-03-07  5:40   ` Nicholas Piggin
2023-03-07  5:52     ` Benjamin Gray
2022-11-28  4:05 ` [RFC PATCH 00/13] Add DEXCR support Russell Currey

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