5.10-stable review patch. If anyone has any objections, please let me know.
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From: Johannes Wikner kwikner@ethz.ch
commit c62fa117c32bd1abed9304c58e0da6940f8c7fc2 upstream.
Since X86_FEATURE_ENTRY_IBPB will invalidate all harmful predictions with IBPB, no software-based untraining of returns is needed anymore. Currently, this change affects retbleed and SRSO mitigations so if either of the mitigations is doing IBPB and the other one does the software sequence, the latter is not needed anymore.
[ bp: Massage commit message. ]
Suggested-by: Borislav Petkov bp@alien8.de Signed-off-by: Johannes Wikner kwikner@ethz.ch Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/bugs.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1061,6 +1061,15 @@ do_cmd_auto:
case RETBLEED_MITIGATION_IBPB: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); + + /* + * IBPB on entry already obviates the need for + * software-based untraining so clear those in case some + * other mitigation like SRSO has selected them. + */ + setup_clear_cpu_cap(X86_FEATURE_UNRET); + setup_clear_cpu_cap(X86_FEATURE_RETHUNK); + mitigate_smt = true;
/* @@ -2461,6 +2470,14 @@ static void __init srso_select_mitigatio if (has_microcode) { setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); srso_mitigation = SRSO_MITIGATION_IBPB; + + /* + * IBPB on entry already obviates the need for + * software-based untraining so clear those in case some + * other mitigation like Retbleed has selected them. + */ + setup_clear_cpu_cap(X86_FEATURE_UNRET); + setup_clear_cpu_cap(X86_FEATURE_RETHUNK); } } else { pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");