diff options
author | Petr Mladek <pmladek@suse.com> | 2019-06-27 10:13:34 +0200 |
---|---|---|
committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2019-06-28 14:20:25 -0400 |
commit | d5b844a2cf507fc7642c9ae80a9d585db3065c28 (patch) | |
tree | e2897b45c766fab7e4df84422d5634df6a07a2d5 /arch | |
parent | 04e03d9a616c19a47178eaca835358610e63a1dd (diff) | |
download | linux-d5b844a2cf507fc7642c9ae80a9d585db3065c28.tar.bz2 |
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.c | 3 |
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; } |