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

Greg KH
2023-02-21T19:30:00Z

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?

thanks,

greg k-h