x86/ftrace: Use alternative RET encoding

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>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 5b4efc927d808b68d5d5a18adaf1991dcd6fef52..24b9fa89aa276cb4a589ab315499230fce7b1b4d 100644 (file)
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -301,7 +301,7 @@ 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)
@@ -357,7 +357,10 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
                goto fail;
 
        ip = trampoline + size;
-       memcpy(ip, retq, RET_SIZE);
+       if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+               __text_gen_insn(ip, 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) {