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x86/retbleed: Add __x86_return_thunk alignment checks 

Add a linker assertion and compute the 0xcc padding dynamically so that
__x86_return_thunk is always cacheline-aligned. Leave the SYM_START()
macro in as the untraining doesn't need ENDBR annotations anyway.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Link: https://lore.kernel.org/r/20230515140726.28689-1-bp@alien8.de
This commit is contained in:
Borislav Petkov (AMD) 2023-05-15 16:07:26 +02:00
parent 7583e8fbdc
commit f220125b99
2 changed files with 5 additions and 1 deletions
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4
arch/x86/kernel/vmlinux.lds.S
View File

@ -508,4 +508,8 @@ INIT_PER_CPU(irq_stack_backing_store);
"fixed_percpu_data is not at start of per-cpu area");
#endif
#ifdef CONFIG_RETHUNK
. = ASSERT((__x86_return_thunk & 0x3f) == 0, "__x86_return_thunk not cacheline-aligned");
#endif
#endif /* CONFIG_X86_64 */

2
arch/x86/lib/retpoline.S
View File

@ -143,7 +143,7 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
* from re-poisioning the BTB prediction.
*/
.align 64
.skip 63, 0xcc
.skip 64 - (__x86_return_thunk - zen_untrain_ret), 0xcc
SYM_START(zen_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
ANNOTATE_NOENDBR
/*