Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1538786 > unrolled thread

[PATCH v3 00/15] livepatch: hybrid consistency model

Back to article view | Back to linux.kernel

Contents

  [PATCH v3 00/15] livepatch: hybrid consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-08 19:20 +0100
    [PATCH v3 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-08 19:20 +0100
    [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-08 19:20 +0100
    [PATCH v3 15/15] livepatch: allow removal of a disabled patch Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-08 19:20 +0100
    [PATCH v3 14/15] livepatch: add /proc/<pid>/patch_state Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-08 19:20 +0100
    Re: [PATCH v3 00/15] livepatch: hybrid consistency model Balbir Singh <bsingharora@gmail.com> - 2016-12-10 06:50 +0100
      Re: [PATCH v3 00/15] livepatch: hybrid consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-12-10 18:20 +0100
        Re: [PATCH v3 00/15] livepatch: hybrid consistency model Balbir Singh <bsingharora@gmail.com> - 2016-12-11 03:10 +0100

#1538786 — [PATCH v3 00/15] livepatch: hybrid consistency model

Dusting the cobwebs off the consistency model again.  This is based on
linux-next/master.

v1 was posted on 2015-02-09:

  https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com

v2 was posted on 2016-04-28:

  https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@redhat.com

The biggest issue from v2 was finding a decent way to detect preemption
and page faults on the stack of a sleeping task.  That problem was
solved by rewriting the x86 stack unwinder.  The new unwinder helps
detect such cases by finding all pt_regs on the stack.  When
preemption/page faults are detected, the stack is considered unreliable
and the patching of the task is deferred.

For more details about the consistency model, see patch 13/15.

---

v3:
- rebase on new x86 unwinder
- force !HAVE_RELIABLE_STACKTRACE arches to use patch->immediate for
  now, because we don't have a way to transition kthreads otherwise
- rebase s390 TIF_PATCH_PENDING patch onto latest entry code
- update barrier comments and move barrier from the end of
  klp_init_transition() to its callers
- "klp_work" -> "klp_transition_work"
- "klp_patch_task()" -> "klp_update_patch_state()"
- explicit _TIF_ALLWORK_MASK
- change klp_reverse_transition() to not try to complete transition.
  instead modify the work queue delay to zero.
- get rid of klp_schedule_work() in favor of calling
  schedule_delayed_work() directly with a KLP_TRANSITION_DELAY
- initialize klp_target_state to KLP_UNDEFINED
- move klp_target_state assignment to before patch->immediate check in
  klp_init_transition()
- rcu_read_lock() in klp_update_patch_state(), test the thread flag in
  patch task, synchronize_rcu() in klp_complete_transition()
- use kstrtobool() in enabled_store()
- change task_rq_lock() argument type to struct rq_flags
- add several WARN_ON_ONCE assertions for klp_target_state and
  task->patch_state

v2:
- "universe" -> "patch state"
- rename klp_update_task_universe() -> klp_patch_task()
- add preempt IRQ tracking (TF_PREEMPT_IRQ)
- fix print_context_stack_reliable() bug
- improve print_context_stack_reliable() comments
- klp_ftrace_handler comment fixes
- add "patch_state" proc file to tid_base_stuff
- schedule work even for !RELIABLE_STACKTRACE
- forked child inherits patch state from parent
- add detailed comment to livepatch.h klp_func definition about the
  klp_func patched/transition state transitions
- update exit_to_usermode_loop() comment
- clear all TIF_KLP_NEED_UPDATE flags in klp_complete_transition()
- remove unnecessary function externs
- add livepatch documentation, sysfs documentation, /proc documentation
- /proc/pid/patch_state: -1 means no patch is currently being applied/reverted
- "TIF_KLP_NEED_UPDATE" -> "TIF_PATCH_PENDING"
- support for s390 and powerpc-le
- don't assume stacks with dynamic ftrace trampolines are reliable
- add _TIF_ALLWORK_MASK info to commit log

v1.9:
- revive from the dead and rebased
- reliable stacks!
- add support for immediate consistency model
- add a ton of comments
- fix up memory barriers
- remove "allow patch modules to be removed" patch for now, it still 
  needs more discussion and thought - it can be done with something
- "proc/pid/universe" -> "proc/pid/patch_status"
- remove WARN_ON_ONCE from !func condition in ftrace handler -- can
  happen because of RCU
- keep klp_mutex private by putting the work_fn in core.c
- convert states from int to boolean
- remove obsolete '@state' comments
- several header file and include improvements suggested by Jiri S
- change kallsyms_lookup_size_offset() errors from EINVAL -> ENOENT
- change proc file permissions S_IRUGO -> USR
- use klp_for_each_object/func helpers

---

Jiri Slaby (1):
  livepatch/s390: reorganize TIF thread flag bits

Josh Poimboeuf (12):
  stacktrace/x86: add function for detecting reliable stack traces
  x86/entry: define _TIF_ALLWORK_MASK flags explicitly
  livepatch: temporary stubs for klp_patch_pending() and
    klp_update_patch_state()
  livepatch/x86: add TIF_PATCH_PENDING thread flag
  livepatch/powerpc: add TIF_PATCH_PENDING thread flag
  livepatch: separate enabled and patched states
  livepatch: remove unnecessary object loaded check
  livepatch: move patching functions into patch.c
  livepatch: use kstrtobool() in enabled_store()
  livepatch: store function sizes
  livepatch: change to a per-task consistency model
  livepatch: add /proc/<pid>/patch_state

Miroslav Benes (2):
  livepatch/s390: add TIF_PATCH_PENDING thread flag
  livepatch: allow removal of a disabled patch

 Documentation/ABI/testing/sysfs-kernel-livepatch |   8 +
 Documentation/filesystems/proc.txt               |  18 +
 Documentation/livepatch/livepatch.txt            | 156 ++++++--
 arch/Kconfig                                     |   6 +
 arch/powerpc/include/asm/thread_info.h           |   4 +-
 arch/powerpc/kernel/signal.c                     |   4 +
 arch/s390/include/asm/thread_info.h              |  24 +-
 arch/s390/kernel/entry.S                         |  31 +-
 arch/x86/Kconfig                                 |   1 +
 arch/x86/entry/common.c                          |   9 +-
 arch/x86/include/asm/thread_info.h               |  11 +-
 arch/x86/include/asm/unwind.h                    |   6 +
 arch/x86/kernel/stacktrace.c                     |  59 ++-
 arch/x86/kernel/unwind_frame.c                   |   1 +
 fs/proc/base.c                                   |  15 +
 include/linux/init_task.h                        |   9 +
 include/linux/livepatch.h                        |  66 ++-
 include/linux/sched.h                            |   3 +
 include/linux/stacktrace.h                       |   8 +-
 kernel/fork.c                                    |   3 +
 kernel/livepatch/Makefile                        |   2 +-
 kernel/livepatch/core.c                          | 446 +++++++++------------
 kernel/livepatch/patch.c                         | 261 ++++++++++++
 kernel/livepatch/patch.h                         |  33 ++
 kernel/livepatch/transition.c                    | 487 +++++++++++++++++++++++
 kernel/livepatch/transition.h                    |  14 +
 kernel/sched/idle.c                              |   4 +
 kernel/stacktrace.c                              |  12 +-
 samples/livepatch/livepatch-sample.c             |   8 +-
 29 files changed, 1367 insertions(+), 342 deletions(-)
 create mode 100644 kernel/livepatch/patch.c
 create mode 100644 kernel/livepatch/patch.h
 create mode 100644 kernel/livepatch/transition.c
 create mode 100644 kernel/livepatch/transition.h

-- 
2.7.4

[toc] | [next] | [standalone]

#1538787 — [PATCH v3 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag

From: Miroslav Benes <mbenes@suse.cz>

Update a task's patch state when returning from a system call or user
space interrupt, or after handling a signal.

This greatly increases the chances of a patch operation succeeding.  If
a task is I/O bound, it can be patched when returning from a system
call.  If a task is CPU bound, it can be patched when returning from an
interrupt.  If a task is sleeping on a to-be-patched function, the user
can send SIGSTOP and SIGCONT to force it to switch.

Since there are two ways the syscall can be restarted on return from a
signal handling process, it is important to clear the flag before
do_signal() is called. Otherwise we could miss the migration if we used
SIGSTOP/SIGCONT procedure or fake signal to migrate patching blocking
tasks. If we place our hook to sysc_work label in entry before
TIF_SIGPENDING is evaluated we kill two birds with one stone. The task
is correctly migrated in all return paths from a syscall.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/s390/include/asm/thread_info.h |  2 ++
 arch/s390/kernel/entry.S            | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 4977668..646845e 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -56,6 +56,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_UPROBE		3	/* breakpointed or single-stepping */
+#define TIF_PATCH_PENDING	4	/* pending live patching update */
 
 #define TIF_31BIT		16	/* 32bit process */
 #define TIF_MEMDIE		17	/* is terminating due to OOM killer */
@@ -74,6 +75,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define _TIF_SIGPENDING		_BITUL(TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	_BITUL(TIF_NEED_RESCHED)
 #define _TIF_UPROBE		_BITUL(TIF_UPROBE)
+#define _TIF_PATCH_PENDING	_BITUL(TIF_PATCH_PENDING)
 
 #define _TIF_31BIT		_BITUL(TIF_31BIT)
 #define _TIF_SINGLE_STEP	_BITUL(TIF_SINGLE_STEP)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 161f4e6..33848a8 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -47,7 +47,7 @@ STACK_SIZE  = 1 << STACK_SHIFT
 STACK_INIT = STACK_SIZE - STACK_FRAME_OVERHEAD - __PT_SIZE
 
 _TIF_WORK	= (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \
-		   _TIF_UPROBE)
+		   _TIF_UPROBE | _TIF_PATCH_PENDING)
 _TIF_TRACE	= (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \
 		   _TIF_SYSCALL_TRACEPOINT)
 _CIF_WORK	= (_CIF_MCCK_PENDING | _CIF_ASCE | _CIF_FPU)
@@ -352,6 +352,11 @@ ENTRY(system_call)
 #endif
 	TSTMSK	__PT_FLAGS(%r11),_PIF_PER_TRAP
 	jo	.Lsysc_singlestep
+#ifdef CONFIG_LIVEPATCH
+	TSTMSK	__TI_flags(%r12),_TIF_PATCH_PENDING
+	jo	.Lsysc_patch_pending	# handle live patching just before
+					# signals and possible syscall restart
+#endif
 	TSTMSK	__TI_flags(%r12),_TIF_SIGPENDING
 	jo	.Lsysc_sigpending
 	TSTMSK	__TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -426,6 +431,16 @@ ENTRY(system_call)
 #endif
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lsysc_patch_pending:
+	lg	%r2,__LC_CURRENT	# pass pointer to task struct
+	larl	%r14,.Lsysc_return
+	jg	klp_update_patch_state
+#endif
+
+#
 # _PIF_PER_TRAP is set, call do_per_trap
 #
 .Lsysc_singlestep:
@@ -674,6 +689,10 @@ ENTRY(io_int_handler)
 	jo	.Lio_mcck_pending
 	TSTMSK	__TI_flags(%r12),_TIF_NEED_RESCHED
 	jo	.Lio_reschedule
+#ifdef CONFIG_LIVEPATCH
+	TSTMSK	__TI_flags(%r12),_TIF_PATCH_PENDING
+	jo	.Lio_patch_pending
+#endif
 	TSTMSK	__TI_flags(%r12),_TIF_SIGPENDING
 	jo	.Lio_sigpending
 	TSTMSK	__TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -720,6 +739,16 @@ ENTRY(io_int_handler)
 	j	.Lio_return
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lio_patch_pending:
+	lg	%r2,__LC_CURRENT	# pass pointer to task struct
+	larl	%r14,.Lio_return
+	jg	klp_update_patch_state
+#endif
+
+#
 # _TIF_SIGPENDING or is set, call do_signal
 #
 .Lio_sigpending:
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1538789 — [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces

For live patching and possibly other use cases, a stack trace is only
useful if it can be assured that it's completely reliable.  Add a new
save_stack_trace_tsk_reliable() function to achieve that.

Scenarios which indicate that a stack trace may be unreliable:

- running task
- interrupt stack
- preemption
- corrupted stack data
- stack grows the wrong way
- stack walk doesn't reach the bottom
- user didn't provide a large enough entries array

Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
determine at build time whether the function is implemented.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/Kconfig                   |  6 +++++
 arch/x86/Kconfig               |  1 +
 arch/x86/include/asm/unwind.h  |  6 +++++
 arch/x86/kernel/stacktrace.c   | 59 +++++++++++++++++++++++++++++++++++++++++-
 arch/x86/kernel/unwind_frame.c |  1 +
 include/linux/stacktrace.h     |  8 +++---
 kernel/stacktrace.c            | 12 +++++++--
 7 files changed, 87 insertions(+), 6 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 13f27c1..d61a133 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -678,6 +678,12 @@ config HAVE_STACK_VALIDATION
 	  Architecture supports the 'objtool check' host tool command, which
 	  performs compile-time stack metadata validation.
 
+config HAVE_RELIABLE_STACKTRACE
+	bool
+	help
+	  Architecture has a save_stack_trace_tsk_reliable() function which
+	  only returns a stack trace if it can guarantee the trace is reliable.
+
 config HAVE_ARCH_HASH
 	bool
 	default n
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 215612c..b4a6663 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -155,6 +155,7 @@ config X86
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_RELIABLE_STACKTRACE		if X86_64 && FRAME_POINTER && STACK_VALIDATION
 	select HAVE_STACK_VALIDATION		if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UNSTABLE_SCHED_CLOCK
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index c5a7f3a..44f86dc 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -11,6 +11,7 @@ struct unwind_state {
 	unsigned long stack_mask;
 	struct task_struct *task;
 	int graph_idx;
+	bool error;
 #ifdef CONFIG_FRAME_POINTER
 	unsigned long *bp;
 	struct pt_regs *regs;
@@ -40,6 +41,11 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
 	__unwind_start(state, task, regs, first_frame);
 }
 
+static inline bool unwind_error(struct unwind_state *state)
+{
+	return state->error;
+}
+
 #ifdef CONFIG_FRAME_POINTER
 
 static inline
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 0653788..3e0cf5e 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -74,6 +74,64 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
+#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
+static int __save_stack_trace_reliable(struct stack_trace *trace,
+				       struct task_struct *task)
+{
+	struct unwind_state state;
+	struct pt_regs *regs;
+	unsigned long addr;
+
+	for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state);
+	     unwind_next_frame(&state)) {
+
+		regs = unwind_get_entry_regs(&state);
+		if (regs) {
+			/*
+			 * Preemption and page faults on the stack can make
+			 * frame pointers unreliable.
+			 */
+			if (!user_mode(regs))
+				return -1;
+
+			/*
+			 * This frame contains the (user mode) pt_regs at the
+			 * end of the stack.  Finish the unwind.
+			 */
+			unwind_next_frame(&state);
+			break;
+		}
+
+		addr = unwind_get_return_address(&state);
+		if (!addr || save_stack_address(trace, addr, false))
+			return -1;
+	}
+
+	if (!unwind_done(&state) || unwind_error(&state))
+		return -1;
+
+	if (trace->nr_entries < trace->max_entries)
+		trace->entries[trace->nr_entries++] = ULONG_MAX;
+
+	return 0;
+}
+
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+				  struct stack_trace *trace)
+{
+	int ret;
+
+	if (!try_get_task_stack(tsk))
+		return -EINVAL;
+
+	ret = __save_stack_trace_reliable(trace, tsk);
+
+	put_task_stack(tsk);
+
+	return ret;
+}
+#endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
+
 /* Userspace stacktrace - based on kernel/trace/trace_sysprof.c */
 
 struct stack_frame_user {
@@ -136,4 +194,3 @@ void save_stack_trace_user(struct stack_trace *trace)
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
-
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index ea7b7f9..f82525a 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -184,6 +184,7 @@ bool unwind_next_frame(struct unwind_state *state)
 			state->bp, state->task->comm,
 			state->task->pid, next_frame);
 	}
+	state->error = true;
 the_end:
 	state->stack_info.type = STACK_TYPE_UNKNOWN;
 	return false;
diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index 0a34489..8e8b67b 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -18,6 +18,8 @@ extern void save_stack_trace_regs(struct pt_regs *regs,
 				  struct stack_trace *trace);
 extern void save_stack_trace_tsk(struct task_struct *tsk,
 				struct stack_trace *trace);
+extern int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+					 struct stack_trace *trace);
 
 extern void print_stack_trace(struct stack_trace *trace, int spaces);
 extern int snprint_stack_trace(char *buf, size_t size,
@@ -29,12 +31,12 @@ extern void save_stack_trace_user(struct stack_trace *trace);
 # define save_stack_trace_user(trace)              do { } while (0)
 #endif
 
-#else
+#else /* !CONFIG_STACKTRACE */
 # define save_stack_trace(trace)			do { } while (0)
 # define save_stack_trace_tsk(tsk, trace)		do { } while (0)
 # define save_stack_trace_user(trace)			do { } while (0)
 # define print_stack_trace(trace, spaces)		do { } while (0)
 # define snprint_stack_trace(buf, size, trace, spaces)	do { } while (0)
-#endif
+#endif /* CONFIG_STACKTRACE */
 
-#endif
+#endif /* __LINUX_STACKTRACE_H */
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index b6e4c16..4ef81dc 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -58,8 +58,8 @@ int snprint_stack_trace(char *buf, size_t size,
 EXPORT_SYMBOL_GPL(snprint_stack_trace);
 
 /*
- * Architectures that do not implement save_stack_trace_tsk or
- * save_stack_trace_regs get this weak alias and a once-per-bootup warning
+ * Architectures that do not implement save_stack_trace_*()
+ * get these weak aliases and once-per-bootup warnings
  * (whenever this facility is utilized - for example by procfs):
  */
 __weak void
@@ -73,3 +73,11 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 {
 	WARN_ONCE(1, KERN_INFO "save_stack_trace_regs() not implemented yet.\n");
 }
+
+__weak int
+save_stack_trace_tsk_reliable(struct task_struct *tsk,
+			      struct stack_trace *trace)
+{
+	WARN_ONCE(1, KERN_INFO "save_stack_tsk_reliable() not implemented yet.\n");
+	return -ENOSYS;
+}
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1538790 — [PATCH v3 15/15] livepatch: allow removal of a disabled patch

From: Miroslav Benes <mbenes@suse.cz>

Currently we do not allow patch module to unload since there is no
method to determine if a task is still running in the patched code.

The consistency model gives us the way because when the unpatching
finishes we know that all tasks were marked as safe to call an original
function. Thus every new call to the function calls the original code
and at the same time no task can be somewhere in the patched code,
because it had to leave that code to be marked as safe.

We can safely let the patch module go after that.

Completion is used for synchronization between module removal and sysfs
infrastructure in a similar way to commit 942e443127e9 ("module: Fix
mod->mkobj.kobj potentially freed too early").

Note that we still do not allow the removal for immediate model, that is
no consistency model. The module refcount may increase in this case if
somebody disables and enables the patch several times. This should not
cause any harm.

With this change a call to try_module_get() is moved to
__klp_enable_patch from klp_register_patch to make module reference
counting symmetric (module_put() is in a patch disable path) and to
allow to take a new reference to a disabled module when being enabled.

Also all kobject_put(&patch->kobj) calls are moved outside of klp_mutex
lock protection to prevent a deadlock situation when
klp_unregister_patch is called and sysfs directories are removed. There
is no need to do the same for other kobject_put() callsites as we
currently do not have their sysfs counterparts.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 Documentation/livepatch/livepatch.txt | 29 ++++---------
 include/linux/livepatch.h             |  3 ++
 kernel/livepatch/core.c               | 80 ++++++++++++++++++++++-------------
 kernel/livepatch/transition.c         | 12 +++++-
 samples/livepatch/livepatch-sample.c  |  1 -
 5 files changed, 72 insertions(+), 53 deletions(-)

diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index f87e742..b0eaaf8 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -265,8 +265,15 @@ section "Livepatch life-cycle" below for more details about these
 two operations.
 
 Module removal is only safe when there are no users of the underlying
-functions.  The immediate consistency model is not able to detect this;
-therefore livepatch modules cannot be removed. See "Limitations" below.
+functions. The immediate consistency model is not able to detect this. The
+code just redirects the functions at the very beginning and it does not
+check if the functions are in use. In other words, it knows when the
+functions get called but it does not know when the functions return.
+Therefore it cannot be decided when the livepatch module can be safely
+removed. This is solved by a hybrid consistency model. When the system is
+transitioned to a new patch state (patched/unpatched) it is guaranteed that
+no task sleeps or runs in the old code.
+
 
 5. Livepatch life-cycle
 =======================
@@ -437,24 +444,6 @@ The current Livepatch implementation has several limitations:
     There is work in progress to remove this limitation.
 
 
-  + Livepatch modules can not be removed.
-
-    The current implementation just redirects the functions at the very
-    beginning. It does not check if the functions are in use. In other
-    words, it knows when the functions get called but it does not
-    know when the functions return. Therefore it can not decide when
-    the livepatch module can be safely removed.
-
-    This will get most likely solved once a more complex consistency model
-    is supported. The idea is that a safe state for patching should also
-    mean a safe state for removing the patch.
-
-    Note that the patch itself might get disabled by writing zero
-    to /sys/kernel/livepatch/<patch>/enabled. It causes that the new
-    code will not longer get called. But it does not guarantee
-    that anyone is not sleeping anywhere in the new code.
-
-
   + Livepatch works reliably only when the dynamic ftrace is located at
     the very beginning of the function.
 
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 8e06fe5..1959e52 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -23,6 +23,7 @@
 
 #include <linux/module.h>
 #include <linux/ftrace.h>
+#include <linux/completion.h>
 
 #if IS_ENABLED(CONFIG_LIVEPATCH)
 
@@ -114,6 +115,7 @@ struct klp_object {
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
  * @enabled:	the patch is enabled (but operation may be incomplete)
+ * @finish:	for waiting till it is safe to remove the patch module
  */
 struct klp_patch {
 	/* external */
@@ -125,6 +127,7 @@ struct klp_patch {
 	struct list_head list;
 	struct kobject kobj;
 	bool enabled;
+	struct completion finish;
 };
 
 #define klp_for_each_object(patch, obj) \
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 22c0c01..cc44f40 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -29,6 +29,7 @@
 #include <linux/livepatch.h>
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
+#include <linux/completion.h>
 #include <asm/cacheflush.h>
 #include "patch.h"
 #include "transition.h"
@@ -377,6 +378,18 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	    !list_prev_entry(patch, list)->enabled)
 		return -EBUSY;
 
+	/*
+	 * A reference is taken on the patch module to prevent it from being
+	 * unloaded.
+	 *
+	 * Note: For immediate (no consistency model) patches we don't allow
+	 * patch modules to unload since there is no safe/sane method to
+	 * determine if a thread is still running in the patched code contained
+	 * in the patch module once the ftrace registration is successful.
+	 */
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
 	pr_notice("enabling patch '%s'\n", patch->mod->name);
 
 	klp_init_transition(patch, KLP_PATCHED);
@@ -471,6 +484,15 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 	mutex_lock(&klp_mutex);
 
+	if (!klp_is_patch_registered(patch)) {
+		/*
+		 * Module with the patch could either disappear meanwhile or is
+		 * not properly initialized yet.
+		 */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	if (patch->enabled == enabled) {
 		/* already in requested state */
 		ret = -EINVAL;
@@ -528,10 +550,10 @@ static struct attribute *klp_patch_attrs[] = {
 
 static void klp_kobj_release_patch(struct kobject *kobj)
 {
-	/*
-	 * Once we have a consistency model we'll need to module_put() the
-	 * patch module here.  See klp_register_patch() for more details.
-	 */
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	complete(&patch->finish);
 }
 
 static struct kobj_type klp_ktype_patch = {
@@ -602,7 +624,6 @@ static void klp_free_patch(struct klp_patch *patch)
 	klp_free_objects_limited(patch, NULL);
 	if (!list_empty(&patch->list))
 		list_del(&patch->list);
-	kobject_put(&patch->kobj);
 }
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
@@ -725,11 +746,14 @@ static int klp_init_patch(struct klp_patch *patch)
 	mutex_lock(&klp_mutex);
 
 	patch->enabled = false;
+	init_completion(&patch->finish);
 
 	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
 				   klp_root_kobj, "%s", patch->mod->name);
-	if (ret)
-		goto unlock;
+	if (ret) {
+		mutex_unlock(&klp_mutex);
+		return ret;
+	}
 
 	klp_for_each_object(patch, obj) {
 		ret = klp_init_object(patch, obj);
@@ -745,9 +769,12 @@ static int klp_init_patch(struct klp_patch *patch)
 
 free:
 	klp_free_objects_limited(patch, obj);
-	kobject_put(&patch->kobj);
-unlock:
+
 	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
 	return ret;
 }
 
@@ -761,23 +788,29 @@ static int klp_init_patch(struct klp_patch *patch)
  */
 int klp_unregister_patch(struct klp_patch *patch)
 {
-	int ret = 0;
+	int ret;
 
 	mutex_lock(&klp_mutex);
 
 	if (!klp_is_patch_registered(patch)) {
 		ret = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	if (patch->enabled) {
 		ret = -EBUSY;
-		goto out;
+		goto err;
 	}
 
 	klp_free_patch(patch);
 
-out:
+	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
+	return 0;
+err:
 	mutex_unlock(&klp_mutex);
 	return ret;
 }
@@ -790,12 +823,13 @@ EXPORT_SYMBOL_GPL(klp_unregister_patch);
  * Initializes the data structure associated with the patch and
  * creates the sysfs interface.
  *
+ * There is no need to take the reference on the patch module here. It is done
+ * later when the patch is enabled.
+ *
  * Return: 0 on success, otherwise error
  */
 int klp_register_patch(struct klp_patch *patch)
 {
-	int ret;
-
 	if (!patch || !patch->mod)
 		return -EINVAL;
 
@@ -816,21 +850,7 @@ int klp_register_patch(struct klp_patch *patch)
 	if (!klp_have_reliable_stack() && !patch->immediate)
 		return -ENOSYS;
 
-	/*
-	 * A reference is taken on the patch module to prevent it from being
-	 * unloaded.  Right now, we don't allow patch modules to unload since
-	 * there is currently no method to determine if a thread is still
-	 * running in the patched code contained in the patch module once
-	 * the ftrace registration is successful.
-	 */
-	if (!try_module_get(patch->mod))
-		return -ENODEV;
-
-	ret = klp_init_patch(patch);
-	if (ret)
-		module_put(patch->mod);
-
-	return ret;
+	return klp_init_patch(patch);
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 4494fe6..dc950d5 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -195,13 +195,21 @@ void klp_complete_transition(void)
 	struct klp_func *func;
 	struct task_struct *g, *task;
 	unsigned int cpu;
+	bool is_immediate = false;
 
 	if (klp_transition_patch->immediate)
 		goto done;
 
-	klp_for_each_object(klp_transition_patch, obj)
-		klp_for_each_func(obj, func)
+	klp_for_each_object(klp_transition_patch, obj) {
+		klp_for_each_func(obj, func) {
 			func->transition = false;
+			if (func->immediate)
+				is_immediate = true;
+		}
+	}
+
+	if (klp_target_state == KLP_UNPATCHED && !is_immediate)
+		module_put(klp_transition_patch->mod);
 
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task) {
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index bb61c65..0625f38 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -89,7 +89,6 @@ static int livepatch_init(void)
 
 static void livepatch_exit(void)
 {
-	WARN_ON(klp_disable_patch(&patch));
 	WARN_ON(klp_unregister_patch(&patch));
 }
 
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1538791 — [PATCH v3 14/15] livepatch: add /proc/<pid>/patch_state

Expose the per-task patch state value so users can determine which tasks
are holding up completion of a patching operation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 Documentation/filesystems/proc.txt | 18 ++++++++++++++++++
 fs/proc/base.c                     | 15 +++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 72624a1..85c501b 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -44,6 +44,7 @@ Table of Contents
   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
   3.9   /proc/<pid>/map_files - Information about memory mapped files
   3.10  /proc/<pid>/timerslack_ns - Task timerslack value
+  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
 
   4	Configuring procfs
   4.1	Mount options
@@ -1886,6 +1887,23 @@ Valid values are from 0 - ULLONG_MAX
 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
 permissions on the task specified to change its timerslack_ns value.
 
+3.11	/proc/<pid>/patch_state - Livepatch patch operation state
+-----------------------------------------------------------------
+When CONFIG_LIVEPATCH is enabled, this file displays the value of the
+patch state for the task.
+
+A value of '-1' indicates that no patch is in transition.
+
+A value of '0' indicates that a patch is in transition and the task is
+unpatched.  If the patch is being enabled, then the task hasn't been
+patched yet.  If the patch is being disabled, then the task has already
+been unpatched.
+
+A value of '1' indicates that a patch is in transition and the task is
+patched.  If the patch is being enabled, then the task has already been
+patched.  If the patch is being disabled, then the task hasn't been
+unpatched yet.
+
 
 ------------------------------------------------------------------------------
 Configuring procfs
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5ea8363..2e1e012 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2841,6 +2841,15 @@ static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
 	return err;
 }
 
+#ifdef CONFIG_LIVEPATCH
+static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
+				struct pid *pid, struct task_struct *task)
+{
+	seq_printf(m, "%d\n", task->patch_state);
+	return 0;
+}
+#endif /* CONFIG_LIVEPATCH */
+
 /*
  * Thread groups
  */
@@ -2940,6 +2949,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 	REG("timers",	  S_IRUGO, proc_timers_operations),
 #endif
 	REG("timerslack_ns", S_IRUGO|S_IWUGO, proc_pid_set_timerslack_ns_operations),
+#ifdef CONFIG_LIVEPATCH
+	ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
+#endif
 };
 
 static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
@@ -3320,6 +3332,9 @@ static const struct pid_entry tid_base_stuff[] = {
 	REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
 	REG("setgroups",  S_IRUGO|S_IWUSR, proc_setgroups_operations),
 #endif
+#ifdef CONFIG_LIVEPATCH
+	ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
+#endif
 };
 
 static int proc_tid_base_readdir(struct file *file, struct dir_context *ctx)
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1539782

On Thu, 2016-12-08 at 12:08 -0600, Josh Poimboeuf wrote:
> Dusting the cobwebs off the consistency model again.  This is based on
> linux-next/master.
> 
> v1 was posted on 2015-02-09:
> 
>   https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com
> 
> v2 was posted on 2016-04-28:
> 
>   https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@redhat.com
> 
> The biggest issue from v2 was finding a decent way to detect preemption
> and page faults on the stack of a sleeping task.  

Could you please elaborate on this? Preemption of a sleeping task and
faults as in the future (time) preemption and faults?

Balbir Singh.

[toc] | [prev] | [next] | [standalone]

#1539863

On Sat, Dec 10, 2016 at 04:46:17PM +1100, Balbir Singh wrote:
> On Thu, 2016-12-08 at 12:08 -0600, Josh Poimboeuf wrote:
> > Dusting the cobwebs off the consistency model again.  This is based on
> > linux-next/master.
> > 
> > v1 was posted on 2015-02-09:
> > 
> >   https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com
> > 
> > v2 was posted on 2016-04-28:
> > 
> >   https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@redhat.com
> > 
> > The biggest issue from v2 was finding a decent way to detect preemption
> > and page faults on the stack of a sleeping task.  
> 
> Could you please elaborate on this? Preemption of a sleeping task and
> faults as in the future (time) preemption and faults?

The normal way for a task to go to sleep is to call schedule().  objtool
ensures the stack trace is reliable in that case, by making sure that
all functions save the frame pointer on the stack before calling out to
another function.

But a task can also go to sleep in a few other ways.  One way is by
preemption, where an interrupt handler interrupts the task and calls
preempt_schedule_irq().  Another way is by a page fault exception.  In
both cases, there's no guarantee that the interrupted function saved the
frame pointer on the stack beforehand.  So the stack trace might be
unreliable.  Fortunately, interrupts and exceptions leave evidence
behind on the stack.  So when walking the stack of a sleeping task, we
can detect when an IRQ or exception occurred, and consider such a stack
unreliable.

-- 
Josh

[toc] | [prev] | [next] | [standalone]

#1539949

On 11/12/16 04:17, Josh Poimboeuf wrote:
> On Sat, Dec 10, 2016 at 04:46:17PM +1100, Balbir Singh wrote:
>> On Thu, 2016-12-08 at 12:08 -0600, Josh Poimboeuf wrote:
>>> Dusting the cobwebs off the consistency model again.  This is based on
>>> linux-next/master.
>>>  
>>> v1 was posted on 2015-02-09:
>>>  
>>>   https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com
>>>  
>>> v2 was posted on 2016-04-28:
>>>  
>>>   https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@redhat.com
>>>  
>>> The biggest issue from v2 was finding a decent way to detect preemption
>>> and page faults on the stack of a sleeping task.  
>>
>> Could you please elaborate on this? Preemption of a sleeping task and
>> faults as in the future (time) preemption and faults?
> 
> The normal way for a task to go to sleep is to call schedule().  objtool
> ensures the stack trace is reliable in that case, by making sure that
> all functions save the frame pointer on the stack before calling out to
> another function.
> 
> But a task can also go to sleep in a few other ways.  One way is by
> preemption, where an interrupt handler interrupts the task and calls
> preempt_schedule_irq().

It's preempted, not sleeping. It's on_rq but not on_cpu.

  Another way is by a page fault exception.  In
> both cases, there's no guarantee that the interrupted function saved the
> frame pointer on the stack beforehand.  So the stack trace might be
> unreliable.  Fortunately, interrupts and exceptions leave evidence
> behind on the stack.  So when walking the stack of a sleeping task, we
> can detect when an IRQ or exception occurred, and consider such a stack
> unreliable.
> 

Thanks for the explanation. I presume a whole lot of this is arch specific
code? I'll look at the patches as well

Balbir

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web