linux-kernel - Re: [PATCH v2 1/2] x86/speculation: Allow enabling STIBP with legacy IBRS

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Message-ID: <Y/UbiZoR98xouEy5@kroah.com>
Date:   Tue, 21 Feb 2023 20:29:13 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     KP Singh <kpsingh@...nel.org>
Cc:     linux-kernel@...r.kernel.org, pjt@...gle.com, evn@...gle.com,
        jpoimboe@...nel.org, tglx@...utronix.de, x86@...nel.org,
        hpa@...or.com, peterz@...radead.org,
        pawan.kumar.gupta@...ux.intel.com, kim.phillips@....com,
        alexandre.chartre@...cle.com, daniel.sneddon@...ux.intel.com,
        corbet@....net, bp@...e.de, linyujun809@...wei.com,
        jmattson@...gle.com,
        José Oliveira <joseloliveira11@...il.com>,
        Rodrigo Branco <rodrigo@...nelhacking.com>,
        Alexandra Sandulescu <aesa@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86/speculation: Allow enabling STIBP with legacy
 IBRS

On Tue, Feb 21, 2023 at 07:49:07PM +0100, KP Singh wrote:
> Setting the IBRS bit implicitly enables STIBP to protect against
> cross-thread branch target injection. With enhanced IBRS, the bit it set
> once and is not cleared again. However, on CPUs with just legacy IBRS,
> IBRS bit set on user -> kernel and cleared on kernel -> user (a.k.a
> KERNEL_IBRS). Clearing this bit also disables the implicitly enabled
> STIBP, thus requiring some form of cross-thread protection in userspace.
> 
> Enable STIBP, either opt-in via prctl or seccomp, or always on depending
> on the choice of mitigation selected via spectre_v2_user.
> 
> Reported-by: José Oliveira <joseloliveira11@...il.com>
> Reported-by: Rodrigo Branco <rodrigo@...nelhacking.com>
> Reviewed-by: Alexandra Sandulescu <aesa@...gle.com>
> Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS")
> Cc: stable@...r.kernel.org
> Signed-off-by: KP Singh <kpsingh@...nel.org>
> ---
>  arch/x86/kernel/cpu/bugs.c | 33 ++++++++++++++++++++++-----------
>  1 file changed, 22 insertions(+), 11 deletions(-)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot