[PATCH 5.15 08/14] x86/ftrace: Use alternative RET encoding

Greg Kroah-Hartman
2022-08-19T15:43:00Z

From: Peter Zijlstra <peterz@infradead.org>

commit 1f001e9da6bbf482311e45e48f53c2bd2179e59c upstream.

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>
[cascardo: use memcpy(text_gen_insn) as there is no __text_gen_insn]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/ftrace.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- 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 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)
@@ -365,7 +365,12 @@ create_trampoline(struct ftrace_ops *ops
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) {