diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-13 14:24:12 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-13 14:24:12 -0700 |
| commit | c5f1e32e323157c71eacc6fe087db8d586ff6cb5 (patch) | |
| tree | a4a74b1e8fec09e91ba8910aba117389a466ce82 /Documentation | |
| parent | 04734361953b8cc30d5552c1abe907ccfc8bc0fa (diff) | |
| parent | e6cfcdda8cbe81eaf821c897369a65fec987b404 (diff) | |
Merge tag 'x86-urgent-2022-08-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fix from Ingo Molnar:
"Fix the 'IBPB mitigated RETBleed' mode of operation on AMD CPUs (not
turned on by default), which also need STIBP enabled (if available) to
be '100% safe' on even the shortest speculation windows"
* tag 'x86-urgent-2022-08-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/bugs: Enable STIBP for IBPB mitigated RETBleed
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index db5de5f0b9d3..d7f30902fda0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5274,20 +5274,33 @@ Speculative Code Execution with Return Instructions) vulnerability. + AMD-based UNRET and IBPB mitigations alone do not stop + sibling threads from influencing the predictions of other + sibling threads. For that reason, STIBP is used on pro- + cessors that support it, and mitigate SMT on processors + that don't. + off - no mitigation auto - automatically select a migitation auto,nosmt - automatically select a mitigation, disabling SMT if necessary for the full mitigation (only on Zen1 and older without STIBP). - ibpb - mitigate short speculation windows on - basic block boundaries too. Safe, highest - perf impact. - unret - force enable untrained return thunks, - only effective on AMD f15h-f17h - based systems. - unret,nosmt - like unret, will disable SMT when STIBP - is not available. + ibpb - On AMD, mitigate short speculation + windows on basic block boundaries too. + Safe, highest perf impact. It also + enables STIBP if present. Not suitable + on Intel. + ibpb,nosmt - Like "ibpb" above but will disable SMT + when STIBP is not available. This is + the alternative for systems which do not + have STIBP. + unret - Force enable untrained return thunks, + only effective on AMD f15h-f17h based + systems. + unret,nosmt - Like unret, but will disable SMT when STIBP + is not available. This is the alternative for + systems which do not have STIBP. Selecting 'auto' will choose a mitigation method at run time according to the CPU. |