x86/ftrace: Use alternative RET encoding

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>
(backported from commit 1f001e9da6bbf482311e45e48f53c2bd2179e59c)
[cascardo: use memcpy(text_gen_insn) as there is no __text_gen_insn]
CVE-2022-29900
CVE-2022-29901
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>