linux-kernel - Re: [PATCH] Documentation: Add powerpc options for spec_store_bypass

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Date:   Mon, 9 Jul 2018 20:19:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...abs.org
Subject: Re: [PATCH] Documentation: Add powerpc options for spec_store_bypass_disable

On Mon, Jul 9, 2018 at 7:08 PM, Michael Ellerman <mpe@...erman.id.au> wrote:
> Document the support for spec_store_bypass_disable that was added for
> powerpc in commit a048a07d7f45 ("powerpc/64s: Add support for a store
> forwarding barrier at kernel entry/exit").
>
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  Documentation/admin-guide/kernel-parameters.txt | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> I tried documenting the differences between the PPC options and X86 ones in one
> section, but it got quite messy, so I went with this instead. Happy to take
> advice on how better to structure it if anyone has opinions.
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index efc7aa7a0670..f320c7168b04 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4060,6 +4060,8 @@
>                         This parameter controls whether the Speculative Store
>                         Bypass optimization is used.
>
> +                       On x86 the options are:
> +
>                         on      - Unconditionally disable Speculative Store Bypass
>                         off     - Unconditionally enable Speculative Store Bypass
>                         auto    - Kernel detects whether the CPU model contains an
> @@ -4075,12 +4077,20 @@
>                         seccomp - Same as "prctl" above, but all seccomp threads
>                                   will disable SSB unless they explicitly opt out.
>
> -                       Not specifying this option is equivalent to
> -                       spec_store_bypass_disable=auto.
> -
>                         Default mitigations:
>                         X86:    If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
>
> +                       On powerpc the options are:
> +
> +                       on,auto - On Power8 and Power9 insert a store-forwarding
> +                                 barrier on kernel entry and exit. On Power7
> +                                 perform a software flush on kernel entry and
> +                                 exit.
> +                       off     - No action.
> +
> +                       Not specifying this option is equivalent to
> +                       spec_store_bypass_disable=auto.
> +
>         spia_io_base=   [HW,MTD]
>         spia_fio_base=
>         spia_pedr=
> --
> 2.14.1
>



-- 
Kees Cook
Pixel Security