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authorPetr Mladek <pmladek@suse.com>2019-06-27 10:13:34 +0200
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-06-28 14:20:25 -0400
commitd5b844a2cf507fc7642c9ae80a9d585db3065c28 (patch)
treee2897b45c766fab7e4df84422d5634df6a07a2d5 /arch
parent04e03d9a616c19a47178eaca835358610e63a1dd (diff)
ftrace/x86: Remove possible deadlock between register_kprobe() and ftrace_run_update_code()
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/ftrace.c3
1 files changed, 3 insertions, 0 deletions
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;
}