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| author | Borislav Petkov (AMD) <bp@alien8.de> | 2023-08-14 21:29:50 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-08-26 13:27:00 +0200 |
| commit | c16d0b3baff418ca09c4f6a7e04f0bfc472187bf (patch) | |
| tree | dd761215540c073ca8d266906343d81597795518 /arch/x86 | |
| parent | 529a9f087a7e03e87dd9c2acd687739e3e348045 (diff) | |
| download | linux-c16d0b3baff418ca09c4f6a7e04f0bfc472187bf.tar.gz | |
x86/srso: Explain the untraining sequences a bit more
commit 9dbd23e42ff0b10c9b02c9e649c76e5228241a8e upstream. 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86')
| -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 08a9faa220fe..455a44aa22fb 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -130,6 +130,25 @@ 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. |