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x86/entry: Have entry_ibpb() invalidate return predictions

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entry_ibpb() should invalidate all indirect predictions, including return
target predictions. Not all IBPB implementations do this, in which case the
fallback is RSB filling.

Prevent SRSO-style hijacks of return predictions following IBPB, as the return
target predictor can be corrupted before the IBPB completes.

  [ bp: Massage. ]

Signed-off-by: Johannes Wikner <kwikner@ethz.ch>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
This commit is contained in:
Johannes Wikner 2024-09-23 20:49:36 +02:00 • committed by Borislav Petkov (AMD)
parent 3ea87dfa31
commit 50e4b3b940
1 changed files with 5 additions and 0 deletions
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5
arch/x86/entry/entry.S
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@ -9,6 +9,8 @@
#include <asm/unwind_hints.h>
#include <asm/segment.h>
#include <asm/cache.h>
#include <asm/cpufeatures.h>
#include <asm/nospec-branch.h>
#include "calling.h"
@ -19,6 +21,9 @@ SYM_FUNC_START(entry_ibpb)
movl $PRED_CMD_IBPB, %eax
xorl %edx, %edx
wrmsr
/* Make sure IBPB clears return stack preductions too. */
FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_BUG_IBPB_NO_RET
RET
SYM_FUNC_END(entry_ibpb)
/* For KVM */