context tracking lacks a few protection mechanisms against instrumentation:
- While the core functions are marked NOKPROBE they lack protection
against function tracing which is required as the function entry/exit
points can be utilized by BPF.
- static functions invoked from the protected functions need to be marked
as well as they can be instrumented otherwise.
- using plain inline allows the compiler to emit traceable and probable
functions.
Fix this by marking the functions noinstr and converting the plain inlines
to __always_inline.
The NOKPROBE_SYMBOL() annotations are removed as the .noinstr.text section
is already excluded from being probed.
Cures the following objtool warnings:
vmlinux.o: warning: objtool: enter_from_user_mode()+0x34: call to __context_tracking_exit() leaves .noinstr.text section
vmlinux.o: warning: objtool: prepare_exit_to_usermode()+0x29: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: syscall_return_slowpath()+0x29: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_syscall_64()+0x7f: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_int80_syscall_32()+0x3d: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_fast_syscall_32()+0x9c: call to __context_tracking_enter() leaves .noinstr.text section
and generates new ones...
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
include/linux/context_tracking.h | 6 +++---
include/linux/context_tracking_state.h | 6 +++---
kernel/context_tracking.c | 14 ++++++++------
3 files changed, 14 insertions(+), 12 deletions(-)
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -33,13 +33,13 @@ static inline void user_exit(void)
}
/* Called with interrupts disabled. */
-static inline void user_enter_irqoff(void)
+static __always_inline void user_enter_irqoff(void)
{
if (context_tracking_enabled())
__context_tracking_enter(CONTEXT_USER);
}
-static inline void user_exit_irqoff(void)
+static __always_inline void user_exit_irqoff(void)
{
if (context_tracking_enabled())
__context_tracking_exit(CONTEXT_USER);
@@ -75,7 +75,7 @@ static inline void exception_exit(enum c
* is enabled. If context tracking is disabled, returns
* CONTEXT_DISABLED. This should be used primarily for debugging.
*/
-static inline enum ctx_state ct_state(void)
+static __always_inline enum ctx_state ct_state(void)
{
return context_tracking_enabled() ?
this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -26,12 +26,12 @@ struct context_tracking {
extern struct static_key_false context_tracking_key;
DECLARE_PER_CPU(struct context_tracking, context_tracking);
-static inline bool context_tracking_enabled(void)
+static __always_inline bool context_tracking_enabled(void)
{
return static_branch_unlikely(&context_tracking_key);
}
-static inline bool context_tracking_enabled_cpu(int cpu)
+static __always_inline bool context_tracking_enabled_cpu(int cpu)
{
return context_tracking_enabled() && per_cpu(context_tracking.active, cpu);
}
@@ -41,7 +41,7 @@ static inline bool context_tracking_enab
return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
}
-static inline bool context_tracking_in_user(void)
+static __always_inline bool context_tracking_in_user(void)
{
return __this_cpu_read(context_tracking.state) == CONTEXT_USER;
}
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -31,7 +31,7 @@ EXPORT_SYMBOL_GPL(context_tracking_key);
DEFINE_PER_CPU(struct context_tracking, context_tracking);
EXPORT_SYMBOL_GPL(context_tracking);
-static bool context_tracking_recursion_enter(void)
+static noinstr bool context_tracking_recursion_enter(void)
{
int recursion;
@@ -45,7 +45,7 @@ static bool context_tracking_recursion_e
return false;
}
-static void context_tracking_recursion_exit(void)
+static __always_inline void context_tracking_recursion_exit(void)
{
__this_cpu_dec(context_tracking.recursion);
}
@@ -59,7 +59,7 @@ static void context_tracking_recursion_e
* instructions to execute won't use any RCU read side critical section
* because this function sets RCU in extended quiescent state.
*/
-void __context_tracking_enter(enum ctx_state state)
+void noinstr __context_tracking_enter(enum ctx_state state)
{
/* Kernel threads aren't supposed to go to userspace */
WARN_ON_ONCE(!current->mm);
@@ -77,8 +77,10 @@ void __context_tracking_enter(enum ctx_s
* on the tick.
*/
if (state == CONTEXT_USER) {
+ instr_begin();
trace_user_enter(0);
vtime_user_enter(current);
+ instr_end();
}
rcu_user_enter();
}
@@ -99,7 +101,6 @@ void __context_tracking_enter(enum ctx_s
}
context_tracking_recursion_exit();
}
-NOKPROBE_SYMBOL(__context_tracking_enter);
EXPORT_SYMBOL_GPL(__context_tracking_enter);
void context_tracking_enter(enum ctx_state state)
@@ -142,7 +143,7 @@ NOKPROBE_SYMBOL(context_tracking_user_en
* This call supports re-entrancy. This way it can be called from any exception
* handler without needing to know if we came from userspace or not.
*/
-void __context_tracking_exit(enum ctx_state state)
+void noinstr __context_tracking_exit(enum ctx_state state)
{
if (!context_tracking_recursion_enter())
return;
@@ -155,15 +156,16 @@ void __context_tracking_exit(enum ctx_st
*/
rcu_user_exit();
if (state == CONTEXT_USER) {
+ instr_begin();
vtime_user_exit(current);
trace_user_exit(0);
+ instr_end();
}
}
__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
}
-NOKPROBE_SYMBOL(__context_tracking_exit);
EXPORT_SYMBOL_GPL(__context_tracking_exit);
void context_tracking_exit(enum ctx_state state)
