x86/xen: Mark cpu_bringup_and_idle() as dead_end_function

commit 9af9dcf11bda3e2c0e24c1acaacb8685ad974e93 upstream.

The asm_cpu_bringup_and_idle() function is required to push the return
value on the stack in order to make ORC happy, but the only reason
objtool doesn't complain is because of a happy accident.

The thing is that asm_cpu_bringup_and_idle() doesn't return, so
validate_branch() never terminates and falls through to the next
function, which in the normal case is the hypercall_page. And that, as
it happens, is 4095 NOPs and a RET.

Make asm_cpu_bringup_and_idle() terminate on it's own, by making the
function it calls as a dead-end. This way we no longer rely on what
code happens to come after.

Fixes: c3881eb58d56 ("x86/xen: Make the secondary CPU idle tasks reliable")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lore.kernel.org/r/20210624095147.693801717@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 06aaf04e629c20d7131815a20221752de8fdc4c5..bae6b261481db0ba9322321b1a06c034a676187c 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -144,6 +144,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
                "usercopy_abort",
                "machine_real_restart",
                "rewind_stack_do_exit",
+               "cpu_bringup_and_idle",
        };
 
        if (!func)