[PATCH 1/3] Revert "x86/ftrace: Use alternative RET encoding"

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This reverts commit 3af2ebf798c52b20de827b9dfec13472ab4a7964.

This temporarily reverts the backport of upstream commit
1f001e9da6bbf482311e45e48f53c2bd2179e59c. It was not correct to copy the
ftrace stub as it would contain a relative jump to the return thunk which
would not apply to the context where it was being copied to, leading to
ftrace support to be broken.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
---
 arch/x86/kernel/ftrace.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index ceab28277546..5080f578236a 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -309,7 +309,7 @@ union ftrace_op_code_union {
 	} __attribute__((packed));
 };
 
-#define RET_SIZE		(IS_ENABLED(CONFIG_RETPOLINE) ? 5 : 1 + IS_ENABLED(CONFIG_SLS))
+#define RET_SIZE		1 + IS_ENABLED(CONFIG_SLS)
 
 static unsigned long
 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
@@ -368,10 +368,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 
 	/* The trampoline ends with ret(q) */
 	retq = (unsigned long)ftrace_stub;
-	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
-		memcpy(ip, text_gen_insn(JMP32_INSN_OPCODE, ip, &__x86_return_thunk), JMP32_INSN_SIZE);
-	else
-		ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
+	ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
 	if (WARN_ON(ret < 0))
 		goto fail;
 
-- 
2.34.1




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