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

Greg KH
2023-02-21T19:47:48Z

On Tue, Feb 21, 2023 at 11:35:29AM -0800, KP Singh wrote:
> On Tue, Feb 21, 2023 at 11:29 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > 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@gmail.com>
> > > Reported-by: Rodrigo Branco <rodrigo@kernelhacking.com>
> > > Reviewed-by: Alexandra Sandulescu <aesa@google.com>
> > > Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: KP Singh <kpsingh@kernel.org>
> > > ---
> > > arch/x86/kernel/cpu/bugs.c | 33 ++++++++++++++++++++++-----------
> > > 1 file changed, 22 insertions(+), 11 deletions(-)
> >
> > Why isn't patch 2/2 for stable as well?
>
> It should be. I actually forgot to remove stable from the first one as
> there are still ongoing discussions and people kept having to "drop
> stable". I can send a v3 with stable Cc'ed. Should it have a fixes
> tag too?

Why does anyone need to "drop stable" from a patch discussion? That's
not a problem, we _WANT_ to see the patch review and discussion also
copied there to be aware of what is coming down the pipeline. So
whomever said that is not correct, sorry.

And yes, a fixes: tag would be nice.

thanks,

greg k-h