diff options
| -rw-r--r-- | arch/x86/lib/retpoline.S | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index 5e85da150e96..cd86aeb5fdd3 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -187,6 +187,25 @@ SYM_CODE_START(srso_alias_return_thunk) SYM_CODE_END(srso_alias_return_thunk) /* + * Some generic notes on the untraining sequences: + * + * They are interchangeable when it comes to flushing potentially wrong + * RET predictions from the BTB. + * + * The SRSO Zen1/2 (MOVABS) untraining sequence is longer than the + * Retbleed sequence because the return sequence done there + * (srso_safe_ret()) is longer and the return sequence must fully nest + * (end before) the untraining sequence. Therefore, the untraining + * sequence must fully overlap the return sequence. + * + * Regarding alignment - the instructions which need to be untrained, + * must all start at a cacheline boundary for Zen1/2 generations. That + * is, instruction sequences starting at srso_safe_ret() and + * the respective instruction sequences at retbleed_return_thunk() + * must start at a cacheline boundary. + */ + +/* * Safety details here pertain to the AMD Zen{1,2} microarchitecture: * 1) The RET at retbleed_return_thunk must be on a 64 byte boundary, for * alignment within the BTB. |