Messages in this thread Patch in this message | | | Date | Thu, 16 Jun 2022 09:44:16 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [ammarfaizi2-block:paulmck/linux-rcu/pmladek.2022.06.15a 133/140] vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section |
| |
On Thu, Jun 16, 2022 at 06:40:21AM -0700, Paul E. McKenney wrote: > On Thu, Jun 16, 2022 at 10:19:18AM +0200, Marco Elver wrote: > > On Wed, 15 Jun 2022 at 23:17, Paul E. McKenney <paulmck@kernel.org> wrote: > > > > > > On Wed, Jun 15, 2022 at 01:40:39PM -0700, Paul E. McKenney wrote: > > > > On Thu, Jun 16, 2022 at 04:26:16AM +0800, kernel test robot wrote: > > > > > tree: https://github.com/ammarfaizi2/linux-block paulmck/linux-rcu/pmladek.2022.06.15a > > > > > head: 0ba7324b44282870af740a5a121add62c7f5f730 > > > > > commit: db21b02f8044e812f8a5e3811f602409290e3ede [133/140] context_tracking: Convert state to atomic_t > > > > > config: x86_64-randconfig-r003-20220516 (https://download.01.org/0day-ci/archive/20220616/202206160411.v3iL3YC0-lkp@intel.com/config) > > > > > compiler: gcc-11 (Debian 11.3.0-3) 11.3.0 > > > > > reproduce (this is a W=1 build): > > > > > # https://github.com/ammarfaizi2/linux-block/commit/db21b02f8044e812f8a5e3811f602409290e3ede > > > > > git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block > > > > > git fetch --no-tags ammarfaizi2-block paulmck/linux-rcu/pmladek.2022.06.15a > > > > > git checkout db21b02f8044e812f8a5e3811f602409290e3ede > > > > > # save the config file > > > > > mkdir build_dir && cp config build_dir/.config > > > > > make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash > > > > > > > > > > If you fix the issue, kindly add following tag where applicable > > > > > Reported-by: kernel test robot <lkp@intel.com> > > > > > > > > > > All warnings (new ones prefixed by >>): > > > > > > > > > > >> vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section > > > > > >> vmlinux.o: warning: objtool: __ct_user_enter+0x7f: call to __kasan_check_read() leaves .noinstr.text section > > > > > > > > Marco, Dmitry, my guess is that this is due to the ct->active check in > > > > both functions. Are we supposed to do something to make this sort of > > > > thing safe for KASAN? > > > > > > This time actually CCing Marco and Dmitry... > > > > It's due to the atomic_read()s within the noinstr function. Within > > noinstr you can use arch_atomic_read() to avoid the instrumentation. > > Thank you, will fix!
And please see below for an alleged fix.
Thanx, Paul
------------------------------------------------------------------------
commit 81e24ca26ee9933bcacf67a61e3f6ae41a025442 Author: Paul E. McKenney <paulmck@kernel.org> Date: Thu Jun 16 09:30:37 2022 -0700
context_tracking: Use arch_atomic_read() in __ct_state for KASAN Context tracking's __ct_state() function can be invoked from noinstr state where RCU is not watching. This means that its use of atomic_read() causes KASAN to invoke the non-noinstr __kasan_check_read() function from the noinstr function __ct_state(). This is problematic because someone tracing the __kasan_check_read() function could get a nasty surprise because of RCU not watching. This commit therefore replaces the __ct_state() function's use of atomic_read() with arch_atomic_read(), which KASAN does not attempt to add instrumention to. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Marco Elver <elver@google.com>
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index 0aecc07fb4f50..81c51e5f03143 100644 --- a/include/linux/context_tracking_state.h +++ b/include/linux/context_tracking_state.h @@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking); static __always_inline int __ct_state(void) { - return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK; + return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK; } #endif
| |