Hi,
I'm requesting a stable merge for commit
1978b3a53a74e3230cd46932b149c6e62e832e9a
("x86/speculation: Allow IBPB to be conditionally enabled on CPUs with
always-on STIBP")
into the stable branch for 5.4. Note, the commit is already queued for
inclusion into the next 5.9 stable release
(https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-5.9/x86-speculation-allow-ibpb-to-be-conditionally-enabl.patch).
The patch fixes an issue where a Spectre-v2-user mitigation could not
be enabled via prctl() on certain AMD CPUs. The issue was introduced
in commit 21998a351512eba4ed5969006f0c55882d995ada
("x86/speculation: Avoid force-disabling IBPB based on STIBP and
enhanced IBRS.")
which was merged into the 5.4 stable branch as commit
6d60d5462a91eb46fb88b016508edfa8ee0bc7c8. This commit also exists in
4.19, 4.14, 4.9, and 4.4, so those kernels are also likely affected by
this bug.
--
Anand K. Mistry
Software Engineer
Google Australia
