[patch 32/38] static_call: Add call depth tracking support

Thomas Gleixner
2022-07-16T23:19:43Z

From: Peter Zijlstra <peterz@infradead.org>

When indirect calls are switched to direct calls then it has to be ensured
that the call target is not the function, but the call thunk when call
depth tracking is enabled. But static calls are available before call
thunks have been set up.

Ensure a second run through the static call patching code after call thunks
have been created. When call thunks are not enabled this has no side
effects.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/alternative.h | 5 +++++
arch/x86/kernel/callthunks.c | 37 +++++++++++++++++++++++++++++++++++++
arch/x86/kernel/static_call.c | 1 +
include/linux/static_call.h | 2 ++
kernel/static_call_inline.c | 23 ++++++++++++++++++-----
5 files changed, 63 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -93,12 +93,17 @@ extern void callthunks_patch_builtin_cal
extern void callthunks_patch_module_calls(struct callthunk_sites *sites,
struct module *mod);
extern void callthunks_module_free(struct module *mod);
+extern void *callthunks_translate_call_dest(void *dest);
#else
static __always_inline void callthunks_patch_builtin_calls(void) {}
static __always_inline void
callthunks_patch_module_calls(struct callthunk_sites *sites,
struct module *mod) {}
static __always_inline void callthunks_module_free(struct module *mod) { }
+static __always_inline void *callthunks_translate_call_dest(void *dest)
+{
+ return dest;
+}
#endif

#ifdef CONFIG_SMP
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -7,6 +7,7 @@
#include <linux/memory.h>
#include <linux/moduleloader.h>
#include <linux/set_memory.h>
+#include <linux/static_call.h>
#include <linux/vmalloc.h>

#include <asm/alternative.h>
@@ -492,6 +493,7 @@ static __init noinline void callthunks_i
if (WARN_ON_ONCE(ret))
return;

+ static_call_force_reinit();
thunks_initialized = true;
}

@@ -511,6 +513,41 @@ void __init callthunks_patch_builtin_cal
mutex_unlock(&text_mutex);
}

+static bool is_module_init_dest(void *dest)
+{
+ bool ret = false;
+
+#ifdef CONFIG_MODULES
+ struct module *mod;
+
+ preempt_disable();
+ mod = __module_address((unsigned long)dest);
+ if (mod && within_module_init((unsigned long)dest, mod))
+ ret = true;
+ preempt_enable();
+#endif
+ return ret;
+}
+
+void *callthunks_translate_call_dest(void *dest)
+{
+ void *thunk;
+
+ lockdep_assert_held(&text_mutex);
+
+ if (!thunks_initialized || skip_addr(dest))
+ return dest;
+
+ thunk = btree_lookup64(&call_thunks, (unsigned long)dest);
+
+ if (thunk)
+ return thunk;
+
+ WARN_ON_ONCE(!is_kernel_inittext((unsigned long)dest) &&
+ !is_module_init_dest(dest));
+ return dest;
+}
+
#ifdef CONFIG_MODULES
void noinline callthunks_patch_module_calls(struct callthunk_sites *cs,
struct module *mod)
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -34,6 +34,7 @@ static void __ref __static_call_transfor

switch (type) {
case CALL:
+ func = callthunks_translate_call_dest(func);
code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
if (func == &__static_call_return0) {
emulate = code;
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -162,6 +162,8 @@ extern void arch_static_call_transform(v

extern int __init static_call_init(void);

+extern void static_call_force_reinit(void);
+
struct static_call_mod {
struct static_call_mod *next;
struct module *mod; /* for vmlinux, mod == NULL */
--- a/kernel/static_call_inline.c
+++ b/kernel/static_call_inline.c
@@ -15,7 +15,18 @@ extern struct static_call_site __start_s
extern struct static_call_tramp_key __start_static_call_tramp_key[],
__stop_static_call_tramp_key[];

-static bool static_call_initialized;
+static int static_call_initialized;
+
+/*
+ * Must be called before early_initcall() to be effective.
+ */
+void static_call_force_reinit(void)
+{
+ if (WARN_ON_ONCE(!static_call_initialized))
+ return;
+
+ static_call_initialized++;
+}

/* mutex to protect key modules/sites */
static DEFINE_MUTEX(static_call_mutex);
@@ -475,7 +486,8 @@ int __init static_call_init(void)
{
int ret;

- if (static_call_initialized)
+ /* See static_call_force_reinit(). */
+ if (static_call_initialized == 1)
return 0;

cpus_read_lock();
@@ -490,11 +502,12 @@ int __init static_call_init(void)
BUG();
}

- static_call_initialized = true;
-
#ifdef CONFIG_MODULES
- register_module_notifier(&static_call_module_nb);
+ if (!static_call_initialized)
+ register_module_notifier(&static_call_module_nb);
#endif
+
+ static_call_initialized = 1;
return 0;
}
early_initcall(static_call_init);