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

KP Singh
2023-02-21T19:35:52Z

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?

>
> thanks,
>
> greg k-h