Re: [PATCH 1/2] kernel: set taint flag 'L' at any kind of lockup

[Kees Cook]

On Fri, Nov 29, 2019 at 04:21:46PM +0300, Konstantin Khlebnikov wrote:
> Any lockup or stall notifies about unexpected lack of progress.
> It's better to know about them for further problem investigations.
> 
> Right now only softlockup has own taint flag. Let's generalize it.
> 
> This patch renames TAINT_SOFTLOCKUP into TAINT_LOCKUP at sets it for:
> - softlockup
> - hardlockup
> - RCU stalls
> - stuck in workqueues
> - detected task hung

This seems reasonable to me. The only nit I have is that it might be
nicer to separate the rename from the new call sites, but if there's no
v2, I'm fine with it this way.

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst   |    2 +-
>  Documentation/admin-guide/tainted-kernels.rst |    8 ++++++--
>  include/linux/kernel.h                        |    2 +-
>  kernel/hung_task.c                            |    2 ++
>  kernel/panic.c                                |    2 +-
>  kernel/rcu/tree_stall.h                       |    1 +
>  kernel/watchdog.c                             |    2 +-
>  kernel/watchdog_hld.c                         |    1 +
>  kernel/workqueue.c                            |    1 +
>  tools/debugging/kernel-chktaint               |    2 +-
>  10 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 032c7cd3cede..60867ec525a4 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -1082,7 +1082,7 @@ ORed together. The letters are seen in "Tainted" line of Oops reports.
>    2048  `(I)`  workaround for bug in platform firmware applied
>    4096  `(O)`  externally-built ("out-of-tree") module was loaded
>    8192  `(E)`  unsigned module was loaded
> - 16384  `(L)`  soft lockup occurred
> + 16384  `(L)`  lockup occurred
>   32768  `(K)`  kernel has been live patched
>   65536  `(X)`  Auxiliary taint, defined and used by for distros
>  131072  `(T)`  The kernel was built with the struct randomization plugin
> diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
> index 71e9184a9079..fc76d0aad9f5 100644
> --- a/Documentation/admin-guide/tainted-kernels.rst
> +++ b/Documentation/admin-guide/tainted-kernels.rst
> @@ -96,7 +96,7 @@ Bit  Log  Number  Reason that got the kernel tainted
>   11  _/I    2048  workaround for bug in platform firmware applied
>   12  _/O    4096  externally-built ("out-of-tree") module was loaded
>   13  _/E    8192  unsigned module was loaded
> - 14  _/L   16384  soft lockup occurred
> + 14  _/L   16384  lockup occurred
>   15  _/K   32768  kernel has been live patched
>   16  _/X   65536  auxiliary taint, defined for and used by distros
>   17  _/T  131072  kernel was built with the struct randomization plugin
> @@ -152,7 +152,11 @@ More detailed explanation for tainting
>   13) ``E`` if an unsigned module has been loaded in a kernel supporting
>       module signature.
>  
> - 14) ``L`` if a soft lockup has previously occurred on the system.
> + 14) ``L`` if some kind of lockup has previously occurred on the system:
> +     - soft/hardlockup, see Documentation/admin-guide/lockup-watchdogs.rst
> +     - RCU stall, see Documentation/RCU/stallwarn.txt
> +     - hung task detected, see CONFIG_DETECT_HUNG_TASK
> +     - kernel workqueue lockup, see CONFIG_WQ_WATCHDOG
>  
>   15) ``K`` if the kernel has been live patched.
>  
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index d83d403dac2e..e8a6808e4f2f 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -591,7 +591,7 @@ extern enum system_states {
>  #define TAINT_FIRMWARE_WORKAROUND	11
>  #define TAINT_OOT_MODULE		12
>  #define TAINT_UNSIGNED_MODULE		13
> -#define TAINT_SOFTLOCKUP		14
> +#define TAINT_LOCKUP			14
>  #define TAINT_LIVEPATCH			15
>  #define TAINT_AUX			16
>  #define TAINT_RANDSTRUCT		17
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 14a625c16cb3..521eb2fbf5fc 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -139,6 +139,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>  		hung_task_show_lock = true;
>  	}
>  
> +	add_taint(TAINT_LOCKUP, LOCKDEP_STILL_OK);
> +
>  	touch_nmi_watchdog();
>  }
>  
> diff --git a/kernel/panic.c b/kernel/panic.c
> index f470a038b05b..d7750a45ca8d 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -372,7 +372,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
>  	[ TAINT_FIRMWARE_WORKAROUND ]	= { 'I', ' ', false },
>  	[ TAINT_OOT_MODULE ]		= { 'O', ' ', true },
>  	[ TAINT_UNSIGNED_MODULE ]	= { 'E', ' ', true },
> -	[ TAINT_SOFTLOCKUP ]		= { 'L', ' ', false },
> +	[ TAINT_LOCKUP ]		= { 'L', ' ', false },
>  	[ TAINT_LIVEPATCH ]		= { 'K', ' ', true },
>  	[ TAINT_AUX ]			= { 'X', ' ', true },
>  	[ TAINT_RANDSTRUCT ]		= { 'T', ' ', true },
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index c0b8c458d8a6..181495efff80 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -74,6 +74,7 @@ early_initcall(check_cpu_stall_init);
>  /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
>  static void panic_on_rcu_stall(void)
>  {
> +	add_taint(TAINT_LOCKUP, LOCKDEP_STILL_OK);
>  	if (sysctl_panic_on_rcu_stall)
>  		panic("RCU Stall\n");
>  }
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index f41334ef0971..d60b195708f7 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -466,7 +466,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
>  			smp_mb__after_atomic();
>  		}
>  
> -		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
> +		add_taint(TAINT_LOCKUP, LOCKDEP_STILL_OK);
>  		if (softlockup_panic)
>  			panic("softlockup: hung tasks");
>  		__this_cpu_write(soft_watchdog_warn, true);
> diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
> index 247bf0b1582c..f77256f47422 100644
> --- a/kernel/watchdog_hld.c
> +++ b/kernel/watchdog_hld.c
> @@ -152,6 +152,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
>  				!test_and_set_bit(0, &hardlockup_allcpu_dumped))
>  			trigger_allbutself_cpu_backtrace();
>  
> +		add_taint(TAINT_LOCKUP, LOCKDEP_STILL_OK);
>  		if (hardlockup_panic)
>  			nmi_panic(regs, "Hard LOCKUP");
>  
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index bc2e09a8ea61..825a92893882 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -5741,6 +5741,7 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
>  			pr_cont_pool_info(pool);
>  			pr_cont(" stuck for %us!\n",
>  				jiffies_to_msecs(jiffies - pool_ts) / 1000);
> +			add_taint(TAINT_LOCKUP, LOCKDEP_STILL_OK);
>  		}
>  	}
>  
> diff --git a/tools/debugging/kernel-chktaint b/tools/debugging/kernel-chktaint
> index 2240cb56e6e5..9f24719d8c80 100755
> --- a/tools/debugging/kernel-chktaint
> +++ b/tools/debugging/kernel-chktaint
> @@ -168,7 +168,7 @@ if [ `expr $T % 2` -eq 0 ]; then
>  	addout " "
>  else
>  	addout "L"
> -	echo " * soft lockup occurred (#14)"
> +	echo " * lockup occurred (#14)"
>  fi
>  
>  T=`expr $T / 2`
> 

-- 
Kees Cook