diff options
| author | Borislav Petkov (AMD) <bp@alien8.de> | 2023-08-14 21:29:50 +0200 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-08-16 21:58:59 +0200 |
| commit | 9dbd23e42ff0b10c9b02c9e649c76e5228241a8e (patch) | |
| tree | 11b7e87f2b12d95c407b46436b80fea199455f0a /arch | |
| parent | 864bcaa38ee44ec6c0e43f79c2d2997b977e26b2 (diff) | |
x86/srso: Explain the untraining sequences a bit more
The goal is to eventually have a proper documentation about all this.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814164447.GFZNpZ/64H4lENIe94@fat_crate.local
Diffstat (limited to 'arch')
| -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. |