In preparation to make clear_bhb_loop() work for CPUs with larger BHB, move the sequence to a macro. This will allow setting the depth of BHB-clearing easily via arguments. No functional change intended. Signed-off-by: Pawan Gupta --- arch/x86/entry/entry_64.S | 37 +++++++++++++++++++++++-------------- 1 file changed, 23 insertions(+), 14 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 886f86790b4467347031bc27d3d761d5cc286da1..a62dbc89c5e75b955ebf6d84f20d157d4bce0253 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1499,11 +1499,6 @@ SYM_CODE_END(rewind_stack_and_make_dead) * from the branch history tracker in the Branch Predictor, therefore removing * user influence on subsequent BTB lookups. * - * It should be used on parts prior to Alder Lake. Newer parts should use the - * BHI_DIS_S hardware control instead. If a pre-Alder Lake part is being - * virtualized on newer hardware the VMM should protect against BHI attacks by - * setting BHI_DIS_S for the guests. - * * CALLs/RETs are necessary to prevent Loop Stream Detector(LSD) from engaging * and not clearing the branch history. The call tree looks like: * @@ -1532,10 +1527,7 @@ SYM_CODE_END(rewind_stack_and_make_dead) * Note, callers should use a speculation barrier like LFENCE immediately after * a call to this function to ensure BHB is cleared before indirect branches. */ -SYM_FUNC_START(clear_bhb_loop) - ANNOTATE_NOENDBR - push %rbp - mov %rsp, %rbp +.macro CLEAR_BHB_LOOP_SEQ movl $5, %ecx ANNOTATE_INTRA_FUNCTION_CALL call 1f @@ -1545,15 +1537,16 @@ SYM_FUNC_START(clear_bhb_loop) * Shift instructions so that the RET is in the upper half of the * cacheline and don't take the slowpath to its_return_thunk. */ - .skip 32 - (.Lret1 - 1f), 0xcc + .skip 32 - (.Lret1_\@ - 1f), 0xcc ANNOTATE_INTRA_FUNCTION_CALL 1: call 2f -.Lret1: RET +.Lret1_\@: + RET .align 64, 0xcc /* - * As above shift instructions for RET at .Lret2 as well. + * As above shift instructions for RET at .Lret2_\@ as well. * - * This should be ideally be: .skip 32 - (.Lret2 - 2f), 0xcc + * This should ideally be: .skip 32 - (.Lret2_\@ - 2f), 0xcc * but some Clang versions (e.g. 18) don't like this. */ .skip 32 - 18, 0xcc @@ -1564,8 +1557,24 @@ SYM_FUNC_START(clear_bhb_loop) jnz 3b sub $1, %ecx jnz 1b -.Lret2: RET +.Lret2_\@: + RET 5: +.endm + +/* + * This should be used on parts prior to Alder Lake. Newer parts should use the + * BHI_DIS_S hardware control instead. If a pre-Alder Lake part is being + * virtualized on newer hardware the VMM should protect against BHI attacks by + * setting BHI_DIS_S for the guests. + */ +SYM_FUNC_START(clear_bhb_loop) + ANNOTATE_NOENDBR + push %rbp + mov %rsp, %rbp + + CLEAR_BHB_LOOP_SEQ + pop %rbp RET SYM_FUNC_END(clear_bhb_loop) -- 2.34.1