From: Dave Martin <Dave.Martin@arm.com>
To: Suzuki K Poulose <Suzuki.Poulose@arm.com>
Cc: mark.rutland@arm.com, ckadabi@codeaurora.org,
ard.biesheuvel@linaro.org, marc.zyngier@arm.com,
catalin.marinas@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, jnair@caviumnetworks.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 10/16] arm64: Make KPTI strict CPU local feature
Date: Mon, 29 Jan 2018 17:24:14 +0000 [thread overview]
Message-ID: <20180129172414.GC5862@e103592.cambridge.arm.com> (raw)
In-Reply-To: <4bf35de5-ae61-93b8-f202-52d734997cc5@arm.com>
On Fri, Jan 26, 2018 at 03:46:59PM +0000, Suzuki K Poulose wrote:
> On 26/01/18 12:25, Dave Martin wrote:
> >On Tue, Jan 23, 2018 at 12:28:03PM +0000, Suzuki K Poulose wrote:
> >>KPTI capability is a security feature which should be enabled
> >>when at least one CPU on the system needs it. Any late CPU
> >>which needs the kernel support, should be prevented from
> >>booting (and thus making the system unsecure) if the feature
> >>was not already enabled.
> >
> >Is there an actual change to behaviour here?
>
> Yes, we now prevent any new CPU from booting if it *matches* the capability,
> which we didn't do earlier.
Ok
> >
> >It's not very obvious from the commit message, or the patch when read in
> >isolation.
> >
>
> I will fix the commit message to indicate the current behavior. How about :
>
> "KPTI is treated as a system wide feature, where we enable the feature
> when all the CPUs on the system suffers from the security vulnerability,
> unless it is enabled via kernel command line. Also, we ignore a late CPU
Maybe "enabled" -> "forcibly enabled", if the command-line really is
supposed to have override semantics (which I guess it is).
> which might need the defense if the KPTI is not enabled, making the system
> insecure. This is not sufficient, as
> we should enable the defense when at least one CPU needs it. Also, if
> it is not enabled at boot-time, we can no longer enable it when a late
> CPU turns up. This patch makes sure that the KPTI is checked on all CPUs
There's some repetition here. Does the following work:
"[...] command line. Also, if a late CPU needs KPTI but KPTI was not
enabled at boot time, the CPU is currently allowed to boot, which is a
potential security vulnerability. This patch ensures that late CPUs
are rejected as appropriate if they need KPTI but it wasn't enabled."
Hmmm. That's no shorter after all. Oh well :P
Cheers
---Dave
next prev parent reply other threads:[~2018-01-29 17:24 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-23 12:27 [PATCH 00/16] arm64: Rework cpu capabilities handling Suzuki K Poulose
2018-01-23 12:27 ` [PATCH 01/16] arm64: capabilities: Update prototype for enable call back Suzuki K Poulose
2018-01-23 14:52 ` Dave Martin
2018-01-23 15:38 ` Suzuki K Poulose
2018-01-25 15:36 ` Dave Martin
2018-01-25 16:57 ` Suzuki K Poulose
2018-01-29 16:35 ` Dave Martin
2018-01-23 12:27 ` [PATCH 02/16] arm64: Move errata work around check on boot CPU Suzuki K Poulose
2018-01-23 14:59 ` Dave Martin
2018-01-23 15:07 ` Suzuki K Poulose
2018-01-23 15:11 ` Dave Martin
2018-01-23 12:27 ` [PATCH 03/16] arm64: Move errata capability processing code Suzuki K Poulose
2018-01-23 12:27 ` [PATCH 04/16] arm64: capabilities: Prepare for fine grained capabilities Suzuki K Poulose
2018-01-23 17:33 ` Dave Martin
2018-01-24 18:45 ` Suzuki K Poulose
2018-01-25 13:43 ` Dave Martin
2018-01-25 17:08 ` Suzuki K Poulose
2018-01-25 17:38 ` Dave Martin
2018-01-25 17:33 ` Dave Martin
2018-01-25 17:56 ` Suzuki K Poulose
2018-01-26 10:00 ` Dave Martin
2018-01-26 12:13 ` Suzuki K Poulose
2018-01-23 12:27 ` [PATCH 05/16] arm64: Add flags to check the safety of a capability for late CPU Suzuki K Poulose
2018-01-26 10:10 ` Dave Martin
2018-01-30 11:17 ` Suzuki K Poulose
2018-01-30 14:56 ` Dave Martin
2018-01-30 15:06 ` Suzuki K Poulose
2018-01-23 12:27 ` [PATCH 06/16] arm64: capabilities: Unify the verification Suzuki K Poulose
2018-01-26 11:08 ` Dave Martin
2018-01-26 12:10 ` Suzuki K Poulose
2018-01-29 16:57 ` Dave Martin
2018-01-23 12:28 ` [PATCH 07/16] arm64: capabilities: Filter the entries based on a given type Suzuki K Poulose
2018-01-26 11:22 ` Dave Martin
2018-01-26 12:21 ` Suzuki K Poulose
2018-01-29 17:06 ` Dave Martin
2018-01-23 12:28 ` [PATCH 08/16] arm64: capabilities: Group handling of features and errata Suzuki K Poulose
2018-01-26 11:47 ` Dave Martin
2018-01-26 12:31 ` Suzuki K Poulose
2018-01-29 17:14 ` Dave Martin
2018-01-29 17:22 ` Suzuki K Poulose
2018-01-30 15:06 ` Dave Martin
2018-01-23 12:28 ` [PATCH 09/16] arm64: capabilities: Introduce strict features based on local CPU Suzuki K Poulose
2018-01-26 12:12 ` Dave Martin
2018-01-30 11:25 ` Suzuki K Poulose
2018-01-23 12:28 ` [PATCH 10/16] arm64: Make KPTI strict CPU local feature Suzuki K Poulose
2018-01-26 12:25 ` Dave Martin
2018-01-26 15:46 ` Suzuki K Poulose
2018-01-29 17:24 ` Dave Martin [this message]
2018-01-23 12:28 ` [PATCH 11/16] arm64: errata: Clean up midr range helpers Suzuki K Poulose
2018-01-26 13:50 ` Dave Martin
2018-01-23 12:28 ` [PATCH 12/16] arm64: Add helpers for checking CPU MIDR against a range Suzuki K Poulose
2018-01-26 14:08 ` Dave Martin
2018-01-23 12:28 ` [PATCH 13/16] arm64: Add support for checking errata based on a list of MIDRS Suzuki K Poulose
2018-01-26 14:16 ` Dave Martin
2018-01-26 15:57 ` Suzuki K Poulose
2018-01-30 15:16 ` Dave Martin
2018-01-30 15:38 ` Suzuki K Poulose
2018-01-30 15:58 ` Dave Martin
2018-01-23 12:28 ` [PATCH 14/16] arm64: Add MIDR encoding for Arm Cortex-A55 and Cortex-A35 Suzuki K Poulose
2018-01-23 12:28 ` [PATCH 15/16] arm64: Delay enabling hardware DBM feature Suzuki K Poulose
2018-01-26 14:41 ` Dave Martin
2018-01-26 16:05 ` Suzuki K Poulose
2018-01-30 15:22 ` Dave Martin
2018-01-23 12:28 ` [PATCH 16/16] arm64: Add work around for Arm Cortex-A55 Erratum 1024718 Suzuki K Poulose
2018-01-26 15:33 ` Dave Martin
2018-01-26 16:29 ` Suzuki K Poulose
2018-01-30 15:27 ` Dave Martin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180129172414.GC5862@e103592.cambridge.arm.com \
--to=dave.martin@arm.com \
--cc=Suzuki.Poulose@arm.com \
--cc=ard.biesheuvel@linaro.org \
--cc=catalin.marinas@arm.com \
--cc=ckadabi@codeaurora.org \
--cc=jnair@caviumnetworks.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marc.zyngier@arm.com \
--cc=mark.rutland@arm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox