From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 14 Jun 2022 23:15:40 +0200
Subject: x86/ftrace: Use alternative RET encoding
Git-commit: 1f001e9da6bbf482311e45e48f53c2bd2179e59c
Patch-mainline: v5.19-rc7
References: bsc#1199657 CVE-2022-29900 CVE-2022-29901

Use the return thunk in ftrace trampolines, if needed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/ftrace.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -308,7 +308,7 @@ union ftrace_op_code_union {
 	} __attribute__((packed));
 };
 
-#define RET_SIZE		1 + IS_ENABLED(CONFIG_SLS)
+#define RET_SIZE		(IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS))
 
 static unsigned long
 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
@@ -364,6 +364,8 @@ create_trampoline(struct ftrace_ops *ops
 		goto fail;
 
 	ip = trampoline + size;
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+		__text_gen_insn(ip, JMP32_INSN_OPCODE, ip, &__x86_return_thunk, JMP32_INSN_SIZE);
 
 	/* The trampoline ends with ret(q) */
 	retq = (unsigned long)ftrace_stub;