x86/ftrace: Use alternative RET encoding

stable inclusion
from stable-v5.10.144
commit 35371fd68807f41a4072c01c166de5425a2a47e5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WL0J
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=35371fd68807f41a4072c01c166de5425a2a47e5

--------------------------------

commit 1f001e9d upstream.

Use the return thunk in ftrace trampolines, if needed.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Reviewed-by: NJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: NBorislav Petkov <bp@suse.de>
[cascardo: use memcpy(text_gen_insn) as there is no __text_gen_insn]
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: NOvidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLin Yujun <linyujun809@huawei.com>
Reviewed-by: NZhang Jianhua <chris.zjh@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

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)
@@ -364,7 +364,12 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 		goto fail;
 
 	ip = trampoline + size;
-	memcpy(ip, retq, RET_SIZE);
+
+	/* The trampoline ends with ret(q) */
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+		memcpy(ip, text_gen_insn(JMP32_INSN_OPCODE, ip, &__x86_return_thunk), JMP32_INSN_SIZE);
+	else
+		memcpy(ip, retq, sizeof(retq));
 
 	/* No need to test direct calls on created trampolines */
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {