6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Johannes Wikner kwikner@ethz.ch
commit 0fad2878642ec46225af2054564932745ac5c765 upstream.
entry_ibpb() is designed to follow Intel's IBPB specification regardless of CPU. This includes invalidating RSB entries.
Hence, if IBPB on VMEXIT has been selected, entry_ibpb() as part of the RET untraining in the VMEXIT path will take care of all BTB and RSB clearing so there's no need to explicitly fill the RSB 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 | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1115,6 +1115,14 @@ do_cmd_auto: setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB); setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); mitigate_smt = true; + + /* + * There is no need for RSB filling: entry_ibpb() ensures + * all predictions, including the RSB, are invalidated, + * regardless of IBPB implementation. + */ + setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); + break;
case RETBLEED_MITIGATION_STUFF: @@ -2622,6 +2630,13 @@ static void __init srso_select_mitigatio if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) { setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT; + + /* + * There is no need for RSB filling: entry_ibpb() ensures + * all predictions, including the RSB, are invalidated, + * regardless of IBPB implementation. + */ + setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT); } } else { pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");