[RFC][PATCH 3/6] x86: Add ENDBR to IRET-to-Self

Peter Zijlstra
2021-11-22T17:14:26Z

The IRET-to-Self chunks trigger forward code references without ENDBR,
fix that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/entry/entry_64.S | 2 ++
arch/x86/include/asm/sync_core.h | 2 ++
2 files changed, 4 insertions(+)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -39,6 +39,7 @@
#include <asm/trapnr.h>
#include <asm/nospec-branch.h>
#include <asm/fsgsbase.h>
+#include <asm/ibt.h>
#include <linux/err.h>

#include "calling.h"
@@ -1309,6 +1310,7 @@ SYM_CODE_START(asm_exc_nmi)
iretq /* continues at repeat_nmi below */
UNWIND_HINT_IRET_REGS
1:
+ ENDBR
#endif

repeat_nmi:
--- a/arch/x86/include/asm/sync_core.h
+++ b/arch/x86/include/asm/sync_core.h
@@ -6,6 +6,7 @@
#include <asm/processor.h>
#include <asm/cpufeature.h>
#include <asm/special_insns.h>
+#include <asm/ibt.h>

#ifdef CONFIG_X86_32
static inline void iret_to_self(void)
@@ -34,6 +35,7 @@ static inline void iret_to_self(void)
"pushq $1f\n\t"
"iretq\n\t"
"1:"
+ ASM_ENDBR
: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
}
#endif /* CONFIG_X86_32 */