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context_tracking: Ensure that the critical path cannot be instrumented

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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@linutronix.de>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134340.811520478@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-03-04 11:05:22 +01:00
parent 20355e5f73
commit 0372007f5a
3 changed files with 14 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

6
include/linux/context_tracking.h
View file

@ -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 ctx_state prev_ctx)
* 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;