From: Petr Mladek pmladek@suse.com
commit d5b844a2cf507fc7642c9ae80a9d585db3065c28 upstream.
The commit 9f255b632bf12c4dd7 ("module: Fix livepatch/ftrace module text permissions race") causes a possible deadlock between register_kprobe() and ftrace_run_update_code() when ftrace is using stop_machine().
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
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 the commit 2d1e38f56622b9b ("kprobes: Cure hotplug lock ordering issues"). Many locks are involved. To be on the safe side, text_mutex must become a low level lock taken after cpu_hotplug_lock.rw_sem.
This can't be achieved easily with the current ftrace design. For example, arm calls set_all_modules_text_rw() already in ftrace_arch_code_modify_prepare(), see arch/arm/kernel/ftrace.c. This functions is called:
+ outside stop_machine() from ftrace_run_update_code() + without stop_machine() from ftrace_module_enable()
Fortunately, the problematic fix is needed only on x86_64. It is the only architecture that calls set_all_modules_text_rw() in ftrace path and supports livepatching at the same time.
Therefore it is enough to move text_mutex handling from the generic kernel/trace/ftrace.c into arch/x86/kernel/ftrace.c:
ftrace_arch_code_modify_prepare() ftrace_arch_code_modify_post_process()
This patch basically reverts the ftrace part of the problematic commit 9f255b632bf12c4dd7 ("module: Fix livepatch/ftrace module text permissions race"). And provides x86_64 specific-fix.
Some refactoring of the ftrace code will be needed when livepatching is implemented for arm or nds32. These architectures call set_all_modules_text_rw() and use stop_machine() at the same time.
Link: http://lkml.kernel.org/r/20190627081334.12793-1-pmladek@suse.com
Fixes: 9f255b632bf12c4dd7 ("module: Fix livepatch/ftrace module text permissions race") Acked-by: Thomas Gleixner tglx@linutronix.de Reported-by: Miroslav Benes mbenes@suse.cz Reviewed-by: Miroslav Benes mbenes@suse.cz Reviewed-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Petr Mladek pmladek@suse.com [ As reviewed by Miroslav Benes mbenes@suse.cz, removed return value of ftrace_run_update_code() as it is a void function. ] Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/ftrace.c | 3 +++ kernel/trace/ftrace.c | 10 +--------- 2 files changed, 4 insertions(+), 9 deletions(-)
--- 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 { set_all_modules_text_ro(); set_kernel_text_ro(); + mutex_unlock(&text_mutex); return 0; }
--- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -35,7 +35,6 @@ #include <linux/hash.h> #include <linux/rcupdate.h> #include <linux/kprobes.h> -#include <linux/memory.h>
#include <trace/events/sched.h>
@@ -2628,12 +2627,10 @@ static void ftrace_run_update_code(int c { int ret;
- mutex_lock(&text_mutex); - ret = ftrace_arch_code_modify_prepare(); FTRACE_WARN_ON(ret); if (ret) - goto out_unlock; + return;
/* * By default we use stop_machine() to modify the code. @@ -2645,9 +2642,6 @@ static void ftrace_run_update_code(int c
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, @@ -5771,7 +5765,6 @@ void ftrace_module_enable(struct module struct ftrace_page *pg;
mutex_lock(&ftrace_lock); - mutex_lock(&text_mutex);
if (ftrace_disabled) goto out_unlock; @@ -5833,7 +5826,6 @@ void ftrace_module_enable(struct module ftrace_arch_code_modify_post_process();
out_unlock: - mutex_unlock(&text_mutex); mutex_unlock(&ftrace_lock);
process_cached_mods(mod->name);