* Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race [not found] ` <20190614170408.1b1162dc@gandalf.local.home> @ 2019-06-26 8:22 ` Miroslav Benes 2019-06-26 13:37 ` Petr Mladek 0 siblings, 1 reply; 5+ messages in thread From: Miroslav Benes @ 2019-06-26 8:22 UTC (permalink / raw) To: Steven Rostedt Cc: Josh Poimboeuf, Jessica Yu, Petr Mladek, Jiri Kosina, Joe Lawrence, linux-kernel, live-patching, Johannes Erdfelt, Ingo Molnar, mhiramat, torvalds, tglx On Fri, 14 Jun 2019, Steven Rostedt wrote: > On Thu, 13 Jun 2019 20:07:22 -0500 > Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > > It's possible for livepatch and ftrace to be toggling a module's text > > permissions at the same time, resulting in the following panic: > > > > [..] > > > The above panic occurs when loading two modules at the same time with > > ftrace enabled, where at least one of the modules is a livepatch module: > > > > CPU0 CPU1 > > klp_enable_patch() > > klp_init_object_loaded() > > module_disable_ro() > > ftrace_module_enable() > > ftrace_arch_code_modify_post_process() > > set_all_modules_text_ro() > > klp_write_object_relocations() > > apply_relocate_add() > > *patches read-only code* - BOOM > > > > A similar race exists when toggling ftrace while loading a livepatch > > module. > > > > Fix it by ensuring that the livepatch and ftrace code patching > > operations -- and their respective permissions changes -- are protected > > by the text_mutex. > > > > Reported-by: Johannes Erdfelt <johannes@erdfelt.com> > > Fixes: 444d13ff10fb ("modules: add ro_after_init support") > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > > Acked-by: Jessica Yu <jeyu@kernel.org> > > Reviewed-by: Petr Mladek <pmladek@suse.com> > > Reviewed-by: Miroslav Benes <mbenes@suse.cz> > > This patch looks uncontroversial. I'm going to pull this one in and > start testing it. And if it works, I'll push to Linus. Triggered this on s390x. Masami CCed and Linus as well, because the patch is in master branch and we are after -rc6. Thomas CCed because of commit 2d1e38f56622 ("kprobes: Cure hotplug lock ordering issues"). ====================================================== WARNING: possible circular locking dependency detected 5.2.0-rc6 #1 Tainted: G O K ------------------------------------------------------ insmod/1393 is trying to acquire lock: 000000002fdee887 (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2e/0x60 but task is already holding lock: 000000005b22fb82 (text_mutex){+.+.}, at: ftrace_run_update_code+0x2a/0xa0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (text_mutex){+.+.}: validate_chain.isra.21+0xb32/0xd70 __lock_acquire+0x4b8/0x928 lock_acquire+0x102/0x230 __mutex_lock+0x88/0x908 mutex_lock_nested+0x32/0x40 register_kprobe+0x254/0x658 init_kprobes+0x11a/0x168 do_one_initcall+0x70/0x318 kernel_init_freeable+0x456/0x508 kernel_init+0x22/0x150 ret_from_fork+0x30/0x34 kernel_thread_starter+0x0/0xc -> #0 (cpu_hotplug_lock.rw_sem){++++}: check_prev_add+0x90c/0xde0 validate_chain.isra.21+0xb32/0xd70 __lock_acquire+0x4b8/0x928 lock_acquire+0x102/0x230 cpus_read_lock+0x62/0xd0 stop_machine+0x2e/0x60 arch_ftrace_update_code+0x2e/0x40 ftrace_run_update_code+0x40/0xa0 ftrace_startup+0xb2/0x168 register_ftrace_function+0x64/0x88 klp_patch_object+0x1a2/0x290 klp_enable_patch+0x554/0x980 do_one_initcall+0x70/0x318 do_init_module+0x6e/0x250 load_module+0x1782/0x1990 __s390x_sys_finit_module+0xaa/0xf0 system_call+0xd8/0x2d0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(text_mutex); lock(cpu_hotplug_lock.rw_sem); lock(text_mutex); lock(cpu_hotplug_lock.rw_sem); *** DEADLOCK *** 3 locks held by insmod/1393: #0: 00000000a9723159 (klp_mutex){+.+.}, at: klp_enable_patch+0x62/0x980 #1: 00000000bd173ffc (ftrace_lock){+.+.}, at: register_ftrace_function+0x56/0x88 #2: 000000005b22fb82 (text_mutex){+.+.}, at: ftrace_run_update_code+0x2a/0xa0 stack backtrace: CPU: 0 PID: 1393 Comm: insmod Tainted: G O K 5.2.0-rc6 #1 Hardware name: IBM 2827 H43 400 (KVM/Linux) Call Trace: ([<00000000682100b4>] show_stack+0xb4/0x130) [<0000000068adeb8c>] dump_stack+0x94/0xd8 [<00000000682b563c>] print_circular_bug+0x1f4/0x328 [<00000000682b7264>] check_prev_add+0x90c/0xde0 [<00000000682b826a>] validate_chain.isra.21+0xb32/0xd70 [<00000000682ba018>] __lock_acquire+0x4b8/0x928 [<00000000682ba952>] lock_acquire+0x102/0x230 [<0000000068243c12>] cpus_read_lock+0x62/0xd0 [<0000000068336bf6>] stop_machine+0x2e/0x60 [<0000000068355b3e>] arch_ftrace_update_code+0x2e/0x40 [<0000000068355b90>] ftrace_run_update_code+0x40/0xa0 [<000000006835971a>] ftrace_startup+0xb2/0x168 [<0000000068359834>] register_ftrace_function+0x64/0x88 [<00000000682e8a9a>] klp_patch_object+0x1a2/0x290 [<00000000682e7d64>] klp_enable_patch+0x554/0x980 [<00000000681fcaa0>] do_one_initcall+0x70/0x318 [<000000006831449e>] do_init_module+0x6e/0x250 [<0000000068312b52>] load_module+0x1782/0x1990 [<0000000068313002>] __s390x_sys_finit_module+0xaa/0xf0 [<0000000068b03f30>] system_call+0xd8/0x2d0 INFO: lockdep is turned off. If I am reading the code correctly, ftrace_run_update_code() takes text_mutex now and then calls stop_machine(), which grabs cpu_hotplug_lock for reading. do_optimize_kprobes() (see the comment there) expects cpu_hotplug_lock to be held and takes text_mutex. Whoops. Maybe there is a simple fix, but reverting the commit in this stage seems warranted. Miroslav ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race 2019-06-26 8:22 ` [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race Miroslav Benes @ 2019-06-26 13:37 ` Petr Mladek 2019-06-26 14:44 ` Thomas Gleixner 0 siblings, 1 reply; 5+ messages in thread From: Petr Mladek @ 2019-06-26 13:37 UTC (permalink / raw) To: Miroslav Benes Cc: Steven Rostedt, Josh Poimboeuf, Jessica Yu, Jiri Kosina, Joe Lawrence, linux-kernel, live-patching, Johannes Erdfelt, Ingo Molnar, mhiramat, torvalds, tglx On Wed 2019-06-26 10:22:45, Miroslav Benes wrote: > On Fri, 14 Jun 2019, Steven Rostedt wrote: > > > On Thu, 13 Jun 2019 20:07:22 -0500 > > Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > > > > It's possible for livepatch and ftrace to be toggling a module's text > > > permissions at the same time, resulting in the following panic: > > > > > > > [..] > > > > > The above panic occurs when loading two modules at the same time with > > > ftrace enabled, where at least one of the modules is a livepatch module: > > > > > > CPU0 CPU1 > > > klp_enable_patch() > > > klp_init_object_loaded() > > > module_disable_ro() > > > ftrace_module_enable() > > > ftrace_arch_code_modify_post_process() > > > set_all_modules_text_ro() > > > klp_write_object_relocations() > > > apply_relocate_add() > > > *patches read-only code* - BOOM > > > > > > A similar race exists when toggling ftrace while loading a livepatch > > > module. > > > > > > Fix it by ensuring that the livepatch and ftrace code patching > > > operations -- and their respective permissions changes -- are protected > > > by the text_mutex. > > > > > > Reported-by: Johannes Erdfelt <johannes@erdfelt.com> > > > Fixes: 444d13ff10fb ("modules: add ro_after_init support") > > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > > > Acked-by: Jessica Yu <jeyu@kernel.org> > > > Reviewed-by: Petr Mladek <pmladek@suse.com> > > > Reviewed-by: Miroslav Benes <mbenes@suse.cz> > > > > This patch looks uncontroversial. I'm going to pull this one in and > > start testing it. And if it works, I'll push to Linus. > > Triggered this on s390x. Masami CCed and Linus as well, because the patch > is in master branch and we are after -rc6. Thomas CCed because of commit > 2d1e38f56622 ("kprobes: Cure hotplug lock ordering issues"). > > ====================================================== > WARNING: possible circular locking dependency detected > 5.2.0-rc6 #1 Tainted: G O K > ------------------------------------------------------ > insmod/1393 is trying to acquire lock: > 000000002fdee887 (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2e/0x60 > > but task is already holding lock: > 000000005b22fb82 (text_mutex){+.+.}, at: ftrace_run_update_code+0x2a/0xa0 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (text_mutex){+.+.}: > validate_chain.isra.21+0xb32/0xd70 > __lock_acquire+0x4b8/0x928 > lock_acquire+0x102/0x230 > __mutex_lock+0x88/0x908 > mutex_lock_nested+0x32/0x40 > register_kprobe+0x254/0x658 > init_kprobes+0x11a/0x168 > do_one_initcall+0x70/0x318 > kernel_init_freeable+0x456/0x508 > kernel_init+0x22/0x150 > ret_from_fork+0x30/0x34 > kernel_thread_starter+0x0/0xc > > -> #0 (cpu_hotplug_lock.rw_sem){++++}: > check_prev_add+0x90c/0xde0 > validate_chain.isra.21+0xb32/0xd70 > __lock_acquire+0x4b8/0x928 > lock_acquire+0x102/0x230 > cpus_read_lock+0x62/0xd0 > stop_machine+0x2e/0x60 > arch_ftrace_update_code+0x2e/0x40 > ftrace_run_update_code+0x40/0xa0 > ftrace_startup+0xb2/0x168 > register_ftrace_function+0x64/0x88 > klp_patch_object+0x1a2/0x290 > klp_enable_patch+0x554/0x980 > do_one_initcall+0x70/0x318 > do_init_module+0x6e/0x250 > load_module+0x1782/0x1990 > __s390x_sys_finit_module+0xaa/0xf0 > system_call+0xd8/0x2d0 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(text_mutex); > lock(cpu_hotplug_lock.rw_sem); > lock(text_mutex); > lock(cpu_hotplug_lock.rw_sem); It is similar problem that has been solved by 2d1e38f56622b9bb5af8 ("kprobes: Cure hotplug lock ordering issues"). This commit solved it by always taking cpu_hotplug_lock.rw_sem before text_mutex inside. If we follow the lock ordering then ftrace has to take text_mutex only when stop_machine() is not called or from code called via stop_machine() parameter. This is not easy with the current design. For example, arm calls set_all_modules_text_rw() already in ftrace_arch_code_modify_prepare(), see arch/arm/kernel/ftrace.c. And it is called: + outside stop_machine() from ftrace_run_update_code() + without stop_machine() from ftrace_module_enable() A conservative solution for 5.2 release would be to move text_mutex locking from the generic kernel/trace/ftrace.c into arch/x86/kernel/ftrace.c: ftrace_arch_code_modify_prepare() ftrace_arch_code_modify_post_process() It should be enough to fix the original problem because x86 is the only architecture that calls set_all_modules_text_rw() in ftrace path and supports livepatching at the same time. We would need to do some refactoring when livepatching is enabled for arm or nds32. The conservative solution: diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 0927bb158ffc..33786044d5ac 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -22,6 +22,7 @@ #include <linux/init.h> #include <linux/list.h> #include <linux/module.h> +#include <linux/memory.h> #include <trace/syscall.h> @@ -35,6 +36,7 @@ int ftrace_arch_code_modify_prepare(void) { + mutex_lock(&text_mutex); set_kernel_text_rw(); set_all_modules_text_rw(); return 0; @@ -44,6 +46,7 @@ int ftrace_arch_code_modify_post_process(void) { set_all_modules_text_ro(); set_kernel_text_ro(); + mutex_unlock(&text_mutex); return 0; } diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 38277af44f5c..d3034a4a3fcc 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -34,7 +34,6 @@ #include <linux/hash.h> #include <linux/rcupdate.h> #include <linux/kprobes.h> -#include <linux/memory.h> #include <trace/events/sched.h> @@ -2611,12 +2610,10 @@ static void ftrace_run_update_code(int command) { int ret; - mutex_lock(&text_mutex); - ret = ftrace_arch_code_modify_prepare(); FTRACE_WARN_ON(ret); if (ret) - goto out_unlock; + return ret; /* * By default we use stop_machine() to modify the code. @@ -2628,9 +2625,6 @@ static void ftrace_run_update_code(int command) ret = ftrace_arch_code_modify_post_process(); FTRACE_WARN_ON(ret); - -out_unlock: - mutex_unlock(&text_mutex); } static void ftrace_run_modify_code(struct ftrace_ops *ops, int command, @@ -5784,7 +5778,6 @@ void ftrace_module_enable(struct module *mod) struct ftrace_page *pg; mutex_lock(&ftrace_lock); - mutex_lock(&text_mutex); if (ftrace_disabled) goto out_unlock; @@ -5846,7 +5839,6 @@ void ftrace_module_enable(struct module *mod) ftrace_arch_code_modify_post_process(); out_unlock: - mutex_unlock(&text_mutex); mutex_unlock(&ftrace_lock); process_cached_mods(mod->name); ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race 2019-06-26 13:37 ` Petr Mladek @ 2019-06-26 14:44 ` Thomas Gleixner 2019-06-26 14:52 ` Josh Poimboeuf 2019-06-26 14:59 ` Steven Rostedt 0 siblings, 2 replies; 5+ messages in thread From: Thomas Gleixner @ 2019-06-26 14:44 UTC (permalink / raw) To: Petr Mladek Cc: Miroslav Benes, Steven Rostedt, Josh Poimboeuf, Jessica Yu, Jiri Kosina, Joe Lawrence, linux-kernel, live-patching, Johannes Erdfelt, Ingo Molnar, mhiramat, torvalds On Wed, 26 Jun 2019, Petr Mladek wrote: > On Wed 2019-06-26 10:22:45, Miroslav Benes wrote: > It is similar problem that has been solved by 2d1e38f56622b9bb5af8 > ("kprobes: Cure hotplug lock ordering issues"). This commit solved > it by always taking cpu_hotplug_lock.rw_sem before text_mutex inside. > > If we follow the lock ordering then ftrace has to take text_mutex > only when stop_machine() is not called or from code called via > stop_machine() parameter. > > This is not easy with the current design. For example, arm calls > set_all_modules_text_rw() already in ftrace_arch_code_modify_prepare(), > see arch/arm/kernel/ftrace.c. And it is called: > > + outside stop_machine() from ftrace_run_update_code() > + without stop_machine() from ftrace_module_enable() > > A conservative solution for 5.2 release would be to move text_mutex > locking from the generic kernel/trace/ftrace.c into > arch/x86/kernel/ftrace.c: > > ftrace_arch_code_modify_prepare() > ftrace_arch_code_modify_post_process() > > It should be enough to fix the original problem because > x86 is the only architecture that calls set_all_modules_text_rw() > in ftrace path and supports livepatching at the same time. Looks correct, but I've paged out all the gory details vs. lock ordering in that area. Thanks, tglx ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race 2019-06-26 14:44 ` Thomas Gleixner @ 2019-06-26 14:52 ` Josh Poimboeuf 2019-06-26 14:59 ` Steven Rostedt 1 sibling, 0 replies; 5+ messages in thread From: Josh Poimboeuf @ 2019-06-26 14:52 UTC (permalink / raw) To: Thomas Gleixner Cc: Petr Mladek, Miroslav Benes, Steven Rostedt, Jessica Yu, Jiri Kosina, Joe Lawrence, linux-kernel, live-patching, Johannes Erdfelt, Ingo Molnar, mhiramat, torvalds On Wed, Jun 26, 2019 at 04:44:45PM +0200, Thomas Gleixner wrote: > On Wed, 26 Jun 2019, Petr Mladek wrote: > > On Wed 2019-06-26 10:22:45, Miroslav Benes wrote: > > It is similar problem that has been solved by 2d1e38f56622b9bb5af8 > > ("kprobes: Cure hotplug lock ordering issues"). This commit solved > > it by always taking cpu_hotplug_lock.rw_sem before text_mutex inside. > > > > If we follow the lock ordering then ftrace has to take text_mutex > > only when stop_machine() is not called or from code called via > > stop_machine() parameter. > > > > This is not easy with the current design. For example, arm calls > > set_all_modules_text_rw() already in ftrace_arch_code_modify_prepare(), > > see arch/arm/kernel/ftrace.c. And it is called: > > > > + outside stop_machine() from ftrace_run_update_code() > > + without stop_machine() from ftrace_module_enable() > > > > A conservative solution for 5.2 release would be to move text_mutex > > locking from the generic kernel/trace/ftrace.c into > > arch/x86/kernel/ftrace.c: > > > > ftrace_arch_code_modify_prepare() > > ftrace_arch_code_modify_post_process() > > > > It should be enough to fix the original problem because > > x86 is the only architecture that calls set_all_modules_text_rw() > > in ftrace path and supports livepatching at the same time. > > Looks correct, but I've paged out all the gory details vs. lock ordering in > that area. Looks good to me as well, Petr can you post a proper patch? -- Josh ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race 2019-06-26 14:44 ` Thomas Gleixner 2019-06-26 14:52 ` Josh Poimboeuf @ 2019-06-26 14:59 ` Steven Rostedt 1 sibling, 0 replies; 5+ messages in thread From: Steven Rostedt @ 2019-06-26 14:59 UTC (permalink / raw) To: Thomas Gleixner Cc: Petr Mladek, Miroslav Benes, Josh Poimboeuf, Jessica Yu, Jiri Kosina, Joe Lawrence, linux-kernel, live-patching, Johannes Erdfelt, Ingo Molnar, mhiramat, torvalds On Wed, 26 Jun 2019 16:44:45 +0200 (CEST) Thomas Gleixner <tglx@linutronix.de> wrote: > > > > It should be enough to fix the original problem because > > x86 is the only architecture that calls set_all_modules_text_rw() > > in ftrace path and supports livepatching at the same time. > > Looks correct, but I've paged out all the gory details vs. lock ordering in > that area. I don't believe ftrace_lock and text_mutex had an order before Petr's initial patches. Reversing them shouldn't be an issue here. They were basically both "leaf" mutexes (not grabbing any mutexes when they are held). -- Steve ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-06-26 14:59 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <cover.1560474114.git.jpoimboe@redhat.com> [not found] ` <ab43d56ab909469ac5d2520c5d944ad6d4abd476.1560474114.git.jpoimboe@redhat.com> [not found] ` <20190614170408.1b1162dc@gandalf.local.home> 2019-06-26 8:22 ` [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race Miroslav Benes 2019-06-26 13:37 ` Petr Mladek 2019-06-26 14:44 ` Thomas Gleixner 2019-06-26 14:52 ` Josh Poimboeuf 2019-06-26 14:59 ` Steven Rostedt
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