Revert "x86/ftrace: Use alternative RET encoding"

This reverts commit 00b136bb6254e0abf6aaafe62c4da5f6c4fea4cb.

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@canonical.com>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 9a8633a6506ca39bffeca51aed36d39d9d9f3185..449e31a2f124084e7b9f2995f09c875c5bbba74f 100644 (file)
--- 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;