[PATCH v4 0/9] fprobe: Introduce fprobe function entry/exit probe

[PATCH v4 0/9] fprobe: Introduce fprobe function entry/exit probe

[Masami Hiramatsu]

Hello Jiri,

Here is the 4th version of fprobe. I fixed some issues on fprobe
and rethook. I dropped out-of-tree patches and Jiri's bpf patch
and add rethook arm/arm64 support and fprobe documentation.
The previous version is here[1];

[1] https://lore.kernel.org/all/164260419349.657731.13913104835063027148.stgit@devnote2/T/#u

The biggest change of this version is supporting ftrace location
conversion correctly. Previous version can not find ftrace location
if the dynamic ftrace nop is not placed a the symbol address.

This series introduces the fprobe, the function entry/exit probe
with multiple probe point support. This also introduces the rethook
for hooking function return as same as kretprobe does. This
abstraction will help us to generalize the fgraph tracer,
because we can just switch it from rethook in fprobe, depending
on the kernel configuration.

The patch [1/9] is from Jiri's series[2].

[2] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#u

I'll continue porting rethook to other archs, and after that replace
the current kretprobe with the rethook. This design change will make
the fgraph/kretprobe integration easier because if fgraph is not available,
kretprobe can use rethook.


Thank you,

---

Jiri Olsa (1):
      ftrace: Add ftrace_set_filter_ips function

Masami Hiramatsu (8):
      fprobe: Add ftrace based probe APIs
      rethook: Add a generic return hook
      rethook: x86: Add rethook x86 implementation
      ARM: rethook: Add rethook arm implementation
      arm64: rethook: Add arm64 rethook implementation
      fprobe: Add exit_handler support
      fprobe: Add sample program for fprobe
      docs: fprobe: Add fprobe description to ftrace-use.rst


 Documentation/trace/fprobe.rst                |  131 +++++++++++
 Documentation/trace/index.rst                 |    1 
 arch/arm/Kconfig                              |    1 
 arch/arm/kernel/stacktrace.c                  |    4 
 arch/arm/probes/Makefile                      |    1 
 arch/arm/probes/rethook.c                     |   71 ++++++
 arch/arm64/Kconfig                            |    1 
 arch/arm64/kernel/probes/Makefile             |    1 
 arch/arm64/kernel/probes/rethook.c            |   25 ++
 arch/arm64/kernel/probes/rethook_trampoline.S |   87 +++++++
 arch/arm64/kernel/stacktrace.c                |    3 
 arch/x86/Kconfig                              |    1 
 arch/x86/include/asm/unwind.h                 |    4 
 arch/x86/kernel/Makefile                      |    1 
 arch/x86/kernel/rethook.c                     |  115 +++++++++
 include/linux/fprobe.h                        |   86 +++++++
 include/linux/ftrace.h                        |    3 
 include/linux/rethook.h                       |   99 ++++++++
 include/linux/sched.h                         |    3 
 kernel/exit.c                                 |    2 
 kernel/fork.c                                 |    3 
 kernel/trace/Kconfig                          |   24 ++
 kernel/trace/Makefile                         |    2 
 kernel/trace/fprobe.c                         |  198 ++++++++++++++++
 kernel/trace/ftrace.c                         |   53 ++++
 kernel/trace/rethook.c                        |  311 +++++++++++++++++++++++++
 samples/Kconfig                               |    7 +
 samples/Makefile                              |    1 
 samples/fprobe/Makefile                       |    3 
 samples/fprobe/fprobe_example.c               |  103 ++++++++
 30 files changed, 1336 insertions(+), 9 deletions(-)
 create mode 100644 Documentation/trace/fprobe.rst
 create mode 100644 arch/arm/probes/rethook.c
 create mode 100644 arch/arm64/kernel/probes/rethook.c
 create mode 100644 arch/arm64/kernel/probes/rethook_trampoline.S
 create mode 100644 arch/x86/kernel/rethook.c
 create mode 100644 include/linux/fprobe.h
 create mode 100644 include/linux/rethook.h
 create mode 100644 kernel/trace/fprobe.c
 create mode 100644 kernel/trace/rethook.c
 create mode 100644 samples/fprobe/Makefile
 create mode 100644 samples/fprobe/fprobe_example.c

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>

[PATCH v4 1/9] ftrace: Add ftrace_set_filter_ips function

[Masami Hiramatsu]

From: Jiri Olsa <jolsa@redhat.com>

Adding ftrace_set_filter_ips function to be able to set filter on
multiple ip addresses at once.

With the kprobe multi attach interface we have cases where we need to
initialize ftrace_ops object with thousands of functions, so having
single function diving into ftrace_hash_move_and_update_ops with
ftrace_lock is faster.

The functions ips are passed as unsigned long array with count.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/ftrace.h |    3 +++
 kernel/trace/ftrace.c  |   53 ++++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 9999e29187de..60847cbce0da 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -512,6 +512,8 @@ struct dyn_ftrace {
 
 int ftrace_set_filter_ip(struct ftrace_ops *ops, unsigned long ip,
 			 int remove, int reset);
+int ftrace_set_filter_ips(struct ftrace_ops *ops, unsigned long *ips,
+			  unsigned int cnt, int remove, int reset);
 int ftrace_set_filter(struct ftrace_ops *ops, unsigned char *buf,
 		       int len, int reset);
 int ftrace_set_notrace(struct ftrace_ops *ops, unsigned char *buf,
@@ -802,6 +804,7 @@ static inline unsigned long ftrace_location(unsigned long ip)
 #define ftrace_regex_open(ops, flag, inod, file) ({ -ENODEV; })
 #define ftrace_set_early_filter(ops, buf, enable) do { } while (0)
 #define ftrace_set_filter_ip(ops, ip, remove, reset) ({ -ENODEV; })
+#define ftrace_set_filter_ips(ops, ips, cnt, remove, reset) ({ -ENODEV; })
 #define ftrace_set_filter(ops, buf, len, reset) ({ -ENODEV; })
 #define ftrace_set_notrace(ops, buf, len, reset) ({ -ENODEV; })
 #define ftrace_free_filter(ops) do { } while (0)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index be5f6b32a012..39350aa38649 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4958,7 +4958,7 @@ ftrace_notrace_write(struct file *file, const char __user *ubuf,
 }
 
 static int
-ftrace_match_addr(struct ftrace_hash *hash, unsigned long ip, int remove)
+__ftrace_match_addr(struct ftrace_hash *hash, unsigned long ip, int remove)
 {
 	struct ftrace_func_entry *entry;
 
@@ -4976,9 +4976,25 @@ ftrace_match_addr(struct ftrace_hash *hash, unsigned long ip, int remove)
 	return add_hash_entry(hash, ip);
 }
 
+static int
+ftrace_match_addr(struct ftrace_hash *hash, unsigned long *ips,
+		  unsigned int cnt, int remove)
+{
+	unsigned int i;
+	int err;
+
+	for (i = 0; i < cnt; i++) {
+		err = __ftrace_match_addr(hash, ips[i], remove);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
 static int
 ftrace_set_hash(struct ftrace_ops *ops, unsigned char *buf, int len,
-		unsigned long ip, int remove, int reset, int enable)
+		unsigned long *ips, unsigned int cnt,
+		int remove, int reset, int enable)
 {
 	struct ftrace_hash **orig_hash;
 	struct ftrace_hash *hash;
@@ -5008,8 +5024,8 @@ ftrace_set_hash(struct ftrace_ops *ops, unsigned char *buf, int len,
 		ret = -EINVAL;
 		goto out_regex_unlock;
 	}
-	if (ip) {
-		ret = ftrace_match_addr(hash, ip, remove);
+	if (ips) {
+		ret = ftrace_match_addr(hash, ips, cnt, remove);
 		if (ret < 0)
 			goto out_regex_unlock;
 	}
@@ -5026,10 +5042,10 @@ ftrace_set_hash(struct ftrace_ops *ops, unsigned char *buf, int len,
 }
 
 static int
-ftrace_set_addr(struct ftrace_ops *ops, unsigned long ip, int remove,
-		int reset, int enable)
+ftrace_set_addr(struct ftrace_ops *ops, unsigned long *ips, unsigned int cnt,
+		int remove, int reset, int enable)
 {
-	return ftrace_set_hash(ops, NULL, 0, ip, remove, reset, enable);
+	return ftrace_set_hash(ops, NULL, 0, ips, cnt, remove, reset, enable);
 }
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
@@ -5634,10 +5650,29 @@ int ftrace_set_filter_ip(struct ftrace_ops *ops, unsigned long ip,
 			 int remove, int reset)
 {
 	ftrace_ops_init(ops);
-	return ftrace_set_addr(ops, ip, remove, reset, 1);
+	return ftrace_set_addr(ops, &ip, 1, remove, reset, 1);
 }
 EXPORT_SYMBOL_GPL(ftrace_set_filter_ip);
 
+/**
+ * ftrace_set_filter_ips - set a functions to filter on in ftrace by addresses
+ * @ops - the ops to set the filter with
+ * @ips - the array of addresses to add to or remove from the filter.
+ * @cnt - the number of addresses in @ips
+ * @remove - non zero to remove ips from the filter
+ * @reset - non zero to reset all filters before applying this filter.
+ *
+ * Filters denote which functions should be enabled when tracing is enabled
+ * If @ips array or any ip specified within is NULL , it fails to update filter.
+ */
+int ftrace_set_filter_ips(struct ftrace_ops *ops, unsigned long *ips,
+			  unsigned int cnt, int remove, int reset)
+{
+	ftrace_ops_init(ops);
+	return ftrace_set_addr(ops, ips, cnt, remove, reset, 1);
+}
+EXPORT_SYMBOL_GPL(ftrace_set_filter_ips);
+
 /**
  * ftrace_ops_set_global_filter - setup ops to use global filters
  * @ops - the ops which will use the global filters
@@ -5659,7 +5694,7 @@ static int
 ftrace_set_regex(struct ftrace_ops *ops, unsigned char *buf, int len,
 		 int reset, int enable)
 {
-	return ftrace_set_hash(ops, buf, len, 0, 0, reset, enable);
+	return ftrace_set_hash(ops, buf, len, NULL, 0, 0, reset, enable);
 }
 
 /**

[PATCH v4 2/9] fprobe: Add ftrace based probe APIs

[Masami Hiramatsu]

The fprobe is a wrapper API for ftrace function tracer.
Unlike kprobes, this probes only supports the function entry, but
it can probe multiple functions by one fprobe. The usage is almost
same as the kprobe, user will specify the function names by
fprobe::syms, the number of syms by fprobe::nentry,
and the user handler by fprobe::entry_handler.

struct fprobe fp = { 0 };
const char *targets[] = { "func1", "func2", "func3"};

fp.handler = user_handler;
fp.nentry = ARRAY_SIZE(targets);
fp.syms = targets;

ret = register_fprobe(&fp);

CAUTION: if user entry handler changes registers including
ip address, it will be applied when returns from the
entry handler. So user handler must recover it.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v4:
  - Fix a memory leak when symbol lookup failed.
  - Use ftrace location address instead of symbol address.
  - Convert the given symbol address to ftrace location automatically.
  - Rename fprobe::ftrace to fprobe::ops.
  - Update the Kconfig description.
---
 include/linux/fprobe.h |   80 ++++++++++++++++++++++++++++
 kernel/trace/Kconfig   |   12 ++++
 kernel/trace/Makefile  |    1 
 kernel/trace/fprobe.c  |  135 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 228 insertions(+)
 create mode 100644 include/linux/fprobe.h
 create mode 100644 kernel/trace/fprobe.c

diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
new file mode 100644
index 000000000000..f7de332b08c2
--- /dev/null
+++ b/include/linux/fprobe.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Simple ftrace probe wrapper */
+#ifndef _LINUX_FPROBE_H
+#define _LINUX_FPROBE_H
+
+#include <linux/compiler.h>
+#include <linux/ftrace.h>
+
+/**
+ * struct fprobe - ftrace based probe.
+ * @syms: The array of symbols to probe.
+ * @addrs: The array of ftrace address of the symbols.
+ * @nentry: The number of entries of @syms or @addrs.
+ * @ops: The ftrace_ops.
+ * @nmissed: The counter for missing events.
+ * @flags: The status flag.
+ * @entry_handler: The callback function for function entry.
+ *
+ * User must set either @syms or @addrs, but not both. If user sets
+ * only @syms, the @addrs are generated when registering the fprobe.
+ * That auto-generated @addrs will be freed when unregistering.
+ */
+struct fprobe {
+	const char		**syms;
+	unsigned long		*addrs;
+	unsigned int		nentry;
+
+	struct ftrace_ops	ops;
+	unsigned long		nmissed;
+	unsigned int		flags;
+	void (*entry_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
+};
+
+#define FPROBE_FL_DISABLED	1
+
+static inline bool fprobe_disabled(struct fprobe *fp)
+{
+	return (fp) ? fp->flags & FPROBE_FL_DISABLED : false;
+}
+
+#ifdef CONFIG_FPROBE
+int register_fprobe(struct fprobe *fp);
+int unregister_fprobe(struct fprobe *fp);
+#else
+static inline int register_fprobe(struct fprobe *fp)
+{
+	return -EOPNOTSUPP;
+}
+static inline int unregister_fprobe(struct fprobe *fp)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+/**
+ * disable_fprobe() - Disable fprobe
+ * @fp: The fprobe to be disabled.
+ *
+ * This will soft-disable @fp. Note that this doesn't remove the ftrace
+ * hooks from the function entry.
+ */
+static inline void disable_fprobe(struct fprobe *fp)
+{
+	if (fp)
+		fp->flags |= FPROBE_FL_DISABLED;
+}
+
+/**
+ * enable_fprobe() - Enable fprobe
+ * @fp: The fprobe to be enabled.
+ *
+ * This will soft-enable @fp.
+ */
+static inline void enable_fprobe(struct fprobe *fp)
+{
+	if (fp)
+		fp->flags &= ~FPROBE_FL_DISABLED;
+}
+
+#endif
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 420ff4bc67fd..23483dd474b0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -223,6 +223,18 @@ config DYNAMIC_FTRACE_WITH_ARGS
 	depends on DYNAMIC_FTRACE
 	depends on HAVE_DYNAMIC_FTRACE_WITH_ARGS
 
+config FPROBE
+	bool "Kernel Function Probe (fprobe)"
+	depends on FUNCTION_TRACER
+	depends on DYNAMIC_FTRACE_WITH_REGS
+	default n
+	help
+	  This option enables kernel function probe (fprobe) based on ftrace,
+	  which is similar to kprobes, but probes only for kernel function
+	  entries and it can probe multiple functions by one fprobe.
+
+	  If unsure, say N.
+
 config FUNCTION_PROFILER
 	bool "Kernel function profiler"
 	depends on FUNCTION_TRACER
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index bedc5caceec7..79255f9de9a4 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -97,6 +97,7 @@ obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o
 obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o
 obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o
 obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o
+obj-$(CONFIG_FPROBE) += fprobe.o
 
 obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o
 
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
new file mode 100644
index 000000000000..748cc34765c1
--- /dev/null
+++ b/kernel/trace/fprobe.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fprobe - Simple ftrace probe wrapper for function entry.
+ */
+#define pr_fmt(fmt) "fprobe: " fmt
+
+#include <linux/fprobe.h>
+#include <linux/kallsyms.h>
+#include <linux/kprobes.h>
+#include <linux/slab.h>
+#include <linux/sort.h>
+
+static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
+			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
+{
+	struct fprobe *fp;
+	int bit;
+
+	fp = container_of(ops, struct fprobe, ops);
+	if (fprobe_disabled(fp))
+		return;
+
+	bit = ftrace_test_recursion_trylock(ip, parent_ip);
+	if (bit < 0) {
+		fp->nmissed++;
+		return;
+	}
+
+	if (fp->entry_handler)
+		fp->entry_handler(fp, ip, ftrace_get_regs(fregs));
+
+	ftrace_test_recursion_unlock(bit);
+}
+NOKPROBE_SYMBOL(fprobe_handler);
+
+/* Convert ftrace location address from symbols */
+static int convert_func_addresses(struct fprobe *fp)
+{
+	unsigned long addr, size;
+	unsigned int i;
+
+	/* Convert symbols to symbol address */
+	if (fp->syms) {
+		fp->addrs = kcalloc(fp->nentry, sizeof(*fp->addrs), GFP_KERNEL);
+		if (!fp->addrs)
+			return -ENOMEM;
+
+		for (i = 0; i < fp->nentry; i++) {
+			fp->addrs[i] = kallsyms_lookup_name(fp->syms[i]);
+			if (!fp->addrs[i])	/* Maybe wrong symbol */
+				goto error;
+		}
+	}
+
+	/* Convert symbol address to ftrace location. */
+	for (i = 0; i < fp->nentry; i++) {
+		if (!kallsyms_lookup_size_offset(fp->addrs[i], &size, NULL))
+			size = MCOUNT_INSN_SIZE;
+		addr = ftrace_location_range(fp->addrs[i], fp->addrs[i] + size);
+		if (!addr) /* No dynamic ftrace there. */
+			goto error;
+		fp->addrs[i] = addr;
+	}
+
+	return 0;
+
+error:
+	kfree(fp->addrs);
+	fp->addrs = NULL;
+	return -ENOENT;
+}
+
+/**
+ * register_fprobe() - Register fprobe to ftrace
+ * @fp: A fprobe data structure to be registered.
+ *
+ * This expects the user set @fp::entry_handler, @fp::syms or @fp:addrs,
+ * and @fp::nentry. If @fp::addrs are set, that will be updated to point
+ * the ftrace location. If @fp::addrs are NULL, this will generate it
+ * from @fp::syms.
+ * Note that you do not set both of @fp::addrs and @fp::syms.
+ */
+int register_fprobe(struct fprobe *fp)
+{
+	int ret;
+
+	if (!fp || !fp->nentry || (!fp->syms && !fp->addrs) ||
+	    (fp->syms && fp->addrs))
+		return -EINVAL;
+
+	ret = convert_func_addresses(fp);
+	if (ret < 0)
+		return ret;
+
+	fp->nmissed = 0;
+	fp->ops.func = fprobe_handler;
+	fp->ops.flags = FTRACE_OPS_FL_SAVE_REGS;
+
+	ret = ftrace_set_filter_ips(&fp->ops, fp->addrs, fp->nentry, 0, 0);
+	if (!ret)
+		ret = register_ftrace_function(&fp->ops);
+
+	if (ret < 0 && fp->syms) {
+		kfree(fp->addrs);
+		fp->addrs = NULL;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(register_fprobe);
+
+/**
+ * unregister_fprobe() - Unregister fprobe from ftrace
+ * @fp: A fprobe data structure to be unregistered.
+ *
+ * Unregister fprobe (and remove ftrace hooks from the function entries).
+ * If the @fp::addrs are generated by register_fprobe(), it will be removed
+ * automatically.
+ */
+int unregister_fprobe(struct fprobe *fp)
+{
+	int ret;
+
+	if (!fp || !fp->nentry || !fp->addrs)
+		return -EINVAL;
+
+	ret = unregister_ftrace_function(&fp->ops);
+
+	if (!ret && fp->syms) {
+		kfree(fp->addrs);
+		fp->addrs = NULL;
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(unregister_fprobe);

[PATCH v4 3/9] rethook: Add a generic return hook

[Masami Hiramatsu]

Add a return hook framework which hooks the function
return. Most of the idea came from the kretprobe, but
this is independent from kretprobe.
Note that this is expected to be used with other
function entry hooking feature, like ftrace, fprobe,
adn kprobes. Eventually this will replace the
kretprobe (e.g. kprobe + rethook = kretprobe), but
at this moment, this is just a additional hook.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v4:
  - Fix rethook_trampoline_handler() loops as same as
    what currently kretprobe does.  This will fix some
    stacktrace issue in the rethook handler.
---
 include/linux/rethook.h |   99 +++++++++++++++
 include/linux/sched.h   |    3 
 kernel/exit.c           |    2 
 kernel/fork.c           |    3 
 kernel/trace/Kconfig    |   11 ++
 kernel/trace/Makefile   |    1 
 kernel/trace/rethook.c  |  311 +++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 430 insertions(+)
 create mode 100644 include/linux/rethook.h
 create mode 100644 kernel/trace/rethook.c

diff --git a/include/linux/rethook.h b/include/linux/rethook.h
new file mode 100644
index 000000000000..39cfbff1a03c
--- /dev/null
+++ b/include/linux/rethook.h
@@ -0,0 +1,99 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Return hooking with list-based shadow stack.
+ */
+#ifndef _LINUX_RETHOOK_H
+#define _LINUX_RETHOOK_H
+
+#include <linux/compiler.h>
+#include <linux/freelist.h>
+#include <linux/llist.h>
+#include <linux/rcupdate.h>
+#include <linux/refcount.h>
+
+struct rethook_node;
+
+typedef void (*rethook_handler_t) (struct rethook_node *, void *, struct pt_regs *);
+
+/**
+ * struct rethook - The rethook management data structure.
+ * @data: The user-defined data storage.
+ * @handler: The user-defined return hook handler.
+ * @pool: The pool of struct rethook_node.
+ * @ref: The reference counter.
+ * @rcu: The rcu_head for deferred freeing.
+ *
+ * Don't embed to another data structure, because this is a self-destructive
+ * data structure when all rethook_node are freed.
+ */
+struct rethook {
+	void			*data;
+	rethook_handler_t	handler;
+	struct freelist_head	pool;
+	refcount_t		ref;
+	struct rcu_head		rcu;
+};
+
+/**
+ * struct rethook_node - The rethook shadow-stack entry node.
+ * @freelist: The freelist, linked to struct rethook::pool.
+ * @rcu: The rcu_head for deferred freeing.
+ * @llist: The llist, linked to a struct task_struct::rethooks.
+ * @rethook: The pointer to the struct rethook.
+ * @ret_addr: The storage for the real return address.
+ * @frame: The stroage for the frame pointer.
+ *
+ * You can embed this with your extended data structure to store any data
+ * on the entry of shadow stack.
+ */
+struct rethook_node {
+	union {
+		struct freelist_node freelist;
+		struct rcu_head      rcu;
+	};
+	struct llist_node	llist;
+	struct rethook		*rethook;
+	unsigned long		ret_addr;
+	unsigned long		frame;
+};
+
+struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
+void rethook_free(struct rethook *rh);
+void rethook_add_node(struct rethook *rh, struct rethook_node *node);
+struct rethook_node *rethook_try_get(struct rethook *rh);
+void rethook_recycle(struct rethook_node *node);
+void rethook_hook(struct rethook_node *node, struct pt_regs *regs);
+unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame,
+				    struct llist_node **cur);
+
+/* Arch dependent code must implement arch_* and trampoline code */
+void arch_rethook_prepare(struct rethook_node *node, struct pt_regs *regs);
+void arch_rethook_trampoline(void);
+
+/**
+ * is_rethook_trampoline() - Check whether the address is rethook trampoline
+ * @addr: The address to be checked
+ *
+ * Return true if the @addr is rethook trampoline address.
+ */
+static inline bool is_rethook_trampoline(unsigned long addr)
+{
+	return addr == (unsigned long)arch_rethook_trampoline;
+}
+
+/* If the architecture needs a fixup the return address, implement it. */
+void arch_rethook_fixup_return(struct pt_regs *regs,
+			       unsigned long correct_ret_addr);
+
+/* Generic trampoline handler, arch code must prepare asm stub */
+unsigned long rethook_trampoline_handler(struct pt_regs *regs,
+					 unsigned long frame);
+
+#ifdef CONFIG_RETHOOK
+void rethook_flush_task(struct task_struct *tk);
+#else
+#define rethook_flush_task(tsk)	do { } while (0)
+#endif
+
+#endif
+
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 78c351e35fec..2bfabf5355b7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1473,6 +1473,9 @@ struct task_struct {
 #ifdef CONFIG_KRETPROBES
 	struct llist_head               kretprobe_instances;
 #endif
+#ifdef CONFIG_RETHOOK
+	struct llist_head               rethooks;
+#endif
 
 #ifdef CONFIG_ARCH_HAS_PARANOID_L1D_FLUSH
 	/*
diff --git a/kernel/exit.c b/kernel/exit.c
index f702a6a63686..a39a321c1f37 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -64,6 +64,7 @@
 #include <linux/compat.h>
 #include <linux/io_uring.h>
 #include <linux/kprobes.h>
+#include <linux/rethook.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -169,6 +170,7 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
 	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
 
 	kprobe_flush_task(tsk);
+	rethook_flush_task(tsk);
 	perf_event_delayed_put(tsk);
 	trace_sched_process_free(tsk);
 	put_task_struct(tsk);
diff --git a/kernel/fork.c b/kernel/fork.c
index 3244cc56b697..ffae38be64c4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2282,6 +2282,9 @@ static __latent_entropy struct task_struct *copy_process(
 #ifdef CONFIG_KRETPROBES
 	p->kretprobe_instances.first = NULL;
 #endif
+#ifdef CONFIG_RETHOOK
+	p->rethooks.first = NULL;
+#endif
 
 	/*
 	 * Ensure that the cgroup subsystem policies allow the new process to be
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 23483dd474b0..4d27e56c6e76 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -10,6 +10,17 @@ config USER_STACKTRACE_SUPPORT
 config NOP_TRACER
 	bool
 
+config HAVE_RETHOOK
+	bool
+
+config RETHOOK
+	bool
+	depends on HAVE_RETHOOK
+	help
+	  Enable generic return hooking feature. This is an internal
+	  API, which will be used by other function-entry hooking
+	  feature like fprobe and kprobes.
+
 config HAVE_FUNCTION_TRACER
 	bool
 	help
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 79255f9de9a4..c6f11a139eac 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -98,6 +98,7 @@ obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o
 obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o
 obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o
 obj-$(CONFIG_FPROBE) += fprobe.o
+obj-$(CONFIG_RETHOOK) += rethook.o
 
 obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o
 
diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
new file mode 100644
index 000000000000..76c9848b44a9
--- /dev/null
+++ b/kernel/trace/rethook.c
@@ -0,0 +1,311 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define pr_fmt(fmt) "rethook: " fmt
+
+#include <linux/bug.h>
+#include <linux/kallsyms.h>
+#include <linux/kprobes.h>
+#include <linux/preempt.h>
+#include <linux/rethook.h>
+#include <linux/slab.h>
+#include <linux/sort.h>
+
+/* Return hook list (shadow stack by list) */
+
+/*
+ * This function is called from delayed_put_task_struct() when a task is
+ * dead and cleaned up to recycle any kretprobe instances associated with
+ * this task. These left over instances represent probed functions that
+ * have been called but will never return.
+ */
+void rethook_flush_task(struct task_struct *tk)
+{
+	struct rethook_node *rhn;
+	struct llist_node *node;
+
+	preempt_disable();
+
+	node = __llist_del_all(&tk->rethooks);
+	while (node) {
+		rhn = container_of(node, struct rethook_node, llist);
+		node = node->next;
+		rethook_recycle(rhn);
+	}
+
+	preempt_enable();
+}
+
+static void rethook_free_rcu(struct rcu_head *head)
+{
+	struct rethook *rh = container_of(head, struct rethook, rcu);
+	struct rethook_node *rhn;
+	struct freelist_node *node;
+	int count = 1;
+
+	node = rh->pool.head;
+	while (node) {
+		rhn = container_of(node, struct rethook_node, freelist);
+		node = node->next;
+		kfree(rhn);
+		count++;
+	}
+
+	/* The rh->ref is the number of pooled node + 1 */
+	if (refcount_sub_and_test(count, &rh->ref))
+		kfree(rh);
+}
+
+/**
+ * rethook_free() - Free struct rethook.
+ * @rh: the struct rethook to be freed.
+ *
+ * Free the rethook. Before calling this function, user must ensure the
+ * @rh::data is cleaned if needed (or, the handler can access it after
+ * calling this function.) This function will set the @rh to be freed
+ * after all rethook_node are freed (not soon). And the caller must
+ * not touch @rh after calling this.
+ */
+void rethook_free(struct rethook *rh)
+{
+	rcu_assign_pointer(rh->handler, NULL);
+
+	call_rcu(&rh->rcu, rethook_free_rcu);
+}
+
+/**
+ * rethook_alloc() - Allocate struct rethook.
+ * @data: a data to pass the @handler when hooking the return.
+ * @handler: the return hook callback function.
+ *
+ * Allocate and initialize a new rethook with @data and @handler.
+ * Return NULL if memory allocation fails or @handler is NULL.
+ * Note that @handler == NULL means this rethook is going to be freed.
+ */
+struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
+{
+	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
+
+	if (!rh || !handler)
+		return NULL;
+
+	rh->data = data;
+	rh->handler = handler;
+	rh->pool.head = NULL;
+	refcount_set(&rh->ref, 1);
+
+	return rh;
+}
+
+/**
+ * rethook_add_node() - Add a new node to the rethook.
+ * @rh: the struct rethook.
+ * @node: the struct rethook_node to be added.
+ *
+ * Add @node to @rh. User must allocate @node (as a part of user's
+ * data structure.) The @node fields are initialized in this function.
+ */
+void rethook_add_node(struct rethook *rh, struct rethook_node *node)
+{
+	node->rethook = rh;
+	freelist_add(&node->freelist, &rh->pool);
+	refcount_inc(&rh->ref);
+}
+
+static void free_rethook_node_rcu(struct rcu_head *head)
+{
+	struct rethook_node *node = container_of(head, struct rethook_node, rcu);
+
+	if (refcount_dec_and_test(&node->rethook->ref))
+		kfree(node->rethook);
+	kfree(node);
+}
+
+/**
+ * rethook_recycle() - return the node to rethook.
+ * @node: The struct rethook_node to be returned.
+ *
+ * Return back the @node to @node::rethook. If the @node::rethook is already
+ * marked as freed, this will free the @node.
+ */
+void rethook_recycle(struct rethook_node *node)
+{
+	lockdep_assert_preemption_disabled();
+
+	if (likely(READ_ONCE(node->rethook->handler)))
+		freelist_add(&node->freelist, &node->rethook->pool);
+	else
+		call_rcu(&node->rcu, free_rethook_node_rcu);
+}
+NOKPROBE_SYMBOL(rethook_recycle);
+
+/**
+ * rethook_try_get() - get an unused rethook node.
+ * @rh: The struct rethook which pools the nodes.
+ *
+ * Get an unused rethook node from @rh. If the node pool is empty, this
+ * will return NULL. Caller must disable preemption.
+ */
+struct rethook_node *rethook_try_get(struct rethook *rh)
+{
+	rethook_handler_t handler = READ_ONCE(rh->handler);
+	struct freelist_node *fn;
+
+	lockdep_assert_preemption_disabled();
+
+	/* Check whether @rh is going to be freed. */
+	if (unlikely(!handler))
+		return NULL;
+
+	fn = freelist_try_get(&rh->pool);
+	if (!fn)
+		return NULL;
+
+	return container_of(fn, struct rethook_node, freelist);
+}
+NOKPROBE_SYMBOL(rethook_try_get);
+
+/**
+ * rethook_hook() - Hook the current function return.
+ * @node: The struct rethook node to hook the function return.
+ * @regs: The struct pt_regs for the function entry.
+ *
+ * Hook the current running function return. This must be called when the
+ * function entry (or at least @regs must be the registers of the function
+ * entry.)
+ */
+void rethook_hook(struct rethook_node *node, struct pt_regs *regs)
+{
+	arch_rethook_prepare(node, regs);
+	__llist_add(&node->llist, &current->rethooks);
+}
+NOKPROBE_SYMBOL(rethook_hook);
+
+/* This assumes the 'tsk' is the current task or the is not running. */
+static unsigned long __rethook_find_ret_addr(struct task_struct *tsk,
+					     struct llist_node **cur)
+{
+	struct rethook_node *rh = NULL;
+	struct llist_node *node = *cur;
+
+	if (!node)
+		node = tsk->rethooks.first;
+	else
+		node = node->next;
+
+	while (node) {
+		rh = container_of(node, struct rethook_node, llist);
+		if (rh->ret_addr != (unsigned long)arch_rethook_trampoline) {
+			*cur = node;
+			return rh->ret_addr;
+		}
+		node = node->next;
+	}
+	return 0;
+}
+NOKPROBE_SYMBOL(__rethook_find_ret_addr);
+
+/**
+ * rethook_find_ret_addr -- Find correct return address modified by rethook
+ * @tsk: Target task
+ * @frame: A frame pointer
+ * @cur: a storage of the loop cursor llist_node pointer for next call
+ *
+ * Find the correct return address modified by a rethook on @tsk in unsigned
+ * long type. If it finds the return address, this returns that address value,
+ * or this returns 0.
+ * The @tsk must be 'current' or a task which is not running. @frame is a hint
+ * to get the currect return address - which is compared with the
+ * rethook::frame field. The @cur is a loop cursor for searching the
+ * kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the
+ * first call, but '@cur' itself must NOT NULL.
+ */
+unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame,
+				    struct llist_node **cur)
+{
+	struct rethook_node *rhn = NULL;
+	unsigned long ret;
+
+	if (WARN_ON_ONCE(!cur))
+		return 0;
+
+	do {
+		ret = __rethook_find_ret_addr(tsk, cur);
+		if (!ret)
+			break;
+		rhn = container_of(*cur, struct rethook_node, llist);
+	} while (rhn->frame != frame);
+
+	return ret;
+}
+NOKPROBE_SYMBOL(rethook_find_ret_addr);
+
+void __weak arch_rethook_fixup_return(struct pt_regs *regs,
+				      unsigned long correct_ret_addr)
+{
+	/*
+	 * Do nothing by default. If the architecture which uses a
+	 * frame pointer to record real return address on the stack,
+	 * it should fill this function to fixup the return address
+	 * so that stacktrace works from the rethook handler.
+	 */
+}
+
+/* This function will be called from each arch-defined trampoline. */
+unsigned long rethook_trampoline_handler(struct pt_regs *regs,
+					 unsigned long frame)
+{
+	struct llist_node *first, *node = NULL;
+	unsigned long correct_ret_addr;
+	rethook_handler_t handler;
+	struct rethook_node *rhn;
+
+	correct_ret_addr = __rethook_find_ret_addr(current, &node);
+	if (!correct_ret_addr) {
+		pr_err("rethook: Return address not found! Maybe there is a bug in the kernel\n");
+		BUG_ON(1);
+	}
+
+	instruction_pointer_set(regs, correct_ret_addr);
+
+	/*
+	 * These loops must be protected from rethook_free_rcu() because those
+	 * are accessing 'rhn->rethook'.
+	 */
+	preempt_disable();
+
+	/*
+	 * Run the handler on the shadow stack. Do not unlink the list here because
+	 * stackdump inside the handlers needs to decode it.
+	 */
+	first = current->rethooks.first;
+	while (first) {
+		rhn = container_of(first, struct rethook_node, llist);
+		if (WARN_ON_ONCE(rhn->frame != frame))
+			break;
+		handler = READ_ONCE(rhn->rethook->handler);
+		if (handler)
+			handler(rhn, rhn->rethook->data, regs);
+
+		if (first == node)
+			break;
+		first = first->next;
+	}
+
+	/* Fixup registers for returning to correct address. */
+	arch_rethook_fixup_return(regs, correct_ret_addr);
+
+	/* Unlink used shadow stack */
+	first = current->rethooks.first;
+	current->rethooks.first = node->next;
+	node->next = NULL;
+
+	while (first) {
+		rhn = container_of(first, struct rethook_node, llist);
+		first = first->next;
+		rethook_recycle(rhn);
+	}
+	preempt_enable();
+
+	return correct_ret_addr;
+}
+NOKPROBE_SYMBOL(rethook_trampoline_handler);

[PATCH v4 4/9] rethook: x86: Add rethook x86 implementation

[Masami Hiramatsu]

Add rethook for x86 implementation. Most of the code
has been copied from kretprobes on x86.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v4:
  - fix stack backtrace as same as kretprobe does.
---
 arch/x86/Kconfig              |    1 
 arch/x86/include/asm/unwind.h |    4 +
 arch/x86/kernel/Makefile      |    1 
 arch/x86/kernel/rethook.c     |  115 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 121 insertions(+)
 create mode 100644 arch/x86/kernel/rethook.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5c2ccb85f2ef..0a7d48a63787 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -219,6 +219,7 @@ config X86
 	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_FUNCTION_ERROR_INJECTION
 	select HAVE_KRETPROBES
+	select HAVE_RETHOOK
 	select HAVE_KVM
 	select HAVE_LIVEPATCH			if X86_64
 	select HAVE_MIXED_BREAKPOINTS_REGS
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index 2a1f8734416d..9fe5f73f22f1 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -5,6 +5,7 @@
 #include <linux/sched.h>
 #include <linux/ftrace.h>
 #include <linux/kprobes.h>
+#include <linux/rethook.h>
 #include <asm/ptrace.h>
 #include <asm/stacktrace.h>
 
@@ -107,6 +108,9 @@ static inline
 unsigned long unwind_recover_kretprobe(struct unwind_state *state,
 				       unsigned long addr, unsigned long *addr_p)
 {
+	if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(addr))
+		return rethook_find_ret_addr(state->task, (unsigned long)addr_p,
+					     &state->kr_cur);
 #ifdef CONFIG_KRETPROBES
 	return is_kretprobe_trampoline(addr) ?
 		kretprobe_find_ret_addr(state->task, addr_p, &state->kr_cur) :
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 2ff3e600f426..66593d8c4d74 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -106,6 +106,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o
 obj-$(CONFIG_TRACING)		+= trace.o
+obj-$(CONFIG_RETHOOK)		+= rethook.o
 obj-$(CONFIG_CRASH_CORE)	+= crash_core_$(BITS).o
 obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC_CORE)	+= relocate_kernel_$(BITS).o crash.o
diff --git a/arch/x86/kernel/rethook.c b/arch/x86/kernel/rethook.c
new file mode 100644
index 000000000000..f2f3b9526e43
--- /dev/null
+++ b/arch/x86/kernel/rethook.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
+ */
+#include <linux/bug.h>
+#include <linux/rethook.h>
+#include <linux/kprobes.h>
+
+#include "kprobes/common.h"
+
+/*
+ * Called from arch_rethook_trampoline
+ */
+__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
+{
+	unsigned long *frame_pointer;
+
+	/* fixup registers */
+	regs->cs = __KERNEL_CS;
+#ifdef CONFIG_X86_32
+	regs->gs = 0;
+#endif
+	regs->ip = (unsigned long)&arch_rethook_trampoline;
+	regs->orig_ax = ~0UL;
+	regs->sp += sizeof(long);
+	frame_pointer = &regs->sp + 1;
+
+	/*
+	 * The return address at 'frame_pointer' is recovered by the
+	 * arch_rethook_fixup_return() which called from this
+	 * rethook_trampoline_handler().
+	 */
+	rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
+
+	/*
+	 * Copy FLAGS to 'pt_regs::sp' so that arch_rethook_trapmoline()
+	 * can do RET right after POPF.
+	 */
+	regs->sp = regs->flags;
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
+
+/*
+ * When a target function returns, this code saves registers and calls
+ * arch_rethook_trampoline_callback(), which calls the rethook handler.
+ */
+asm(
+	".text\n"
+	".global arch_rethook_trampoline\n"
+	".type arch_rethook_trampoline, @function\n"
+	"arch_rethook_trampoline:\n"
+#ifdef CONFIG_X86_64
+	/* Push a fake return address to tell the unwinder it's a kretprobe. */
+	"	pushq $arch_rethook_trampoline\n"
+	UNWIND_HINT_FUNC
+	/* Save the 'sp - 8', this will be fixed later. */
+	"	pushq %rsp\n"
+	"	pushfq\n"
+	SAVE_REGS_STRING
+	"	movq %rsp, %rdi\n"
+	"	call arch_rethook_trampoline_callback\n"
+	RESTORE_REGS_STRING
+	/* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
+	"	addq $8, %rsp\n"
+	"	popfq\n"
+#else
+	/* Push a fake return address to tell the unwinder it's a kretprobe. */
+	"	pushl $arch_rethook_trampoline\n"
+	UNWIND_HINT_FUNC
+	/* Save the 'sp - 4', this will be fixed later. */
+	"	pushl %esp\n"
+	"	pushfl\n"
+	SAVE_REGS_STRING
+	"	movl %esp, %eax\n"
+	"	call arch_rethook_trampoline_callback\n"
+	RESTORE_REGS_STRING
+	/* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
+	"	addl $4, %esp\n"
+	"	popfl\n"
+#endif
+	"	ret\n"
+	".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
+);
+NOKPROBE_SYMBOL(arch_rethook_trampoline);
+/*
+ * arch_rethook_trampoline() skips updating frame pointer. The frame pointer
+ * saved in arch_rethook_trampoline_callback() points to the real caller
+ * function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
+ * a standard stack frame with CONFIG_FRAME_POINTER=y.
+ * Let's mark it non-standard function. Anyway, FP unwinder can correctly
+ * unwind without the hint.
+ */
+STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
+
+/* This is called from rethook_trampoline_handler(). */
+void arch_rethook_fixup_return(struct pt_regs *regs,
+			       unsigned long correct_ret_addr)
+{
+	unsigned long *frame_pointer = &regs->sp + 1;
+
+	/* Replace fake return address with real one. */
+	*frame_pointer = correct_ret_addr;
+}
+
+void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs)
+{
+	unsigned long *stack = (unsigned long *)regs->sp;
+
+	rh->ret_addr = stack[0];
+	rh->frame = regs->sp;
+
+	/* Replace the return addr with trampoline addr */
+	stack[0] = (unsigned long) arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare);

[PATCH v4 5/9] ARM: rethook: Add rethook arm implementation

[Masami Hiramatsu]

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 arch/arm/Kconfig             |    1 +
 arch/arm/kernel/stacktrace.c |    4 ++
 arch/arm/probes/Makefile     |    1 +
 arch/arm/probes/rethook.c    |   71 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+)
 create mode 100644 arch/arm/probes/rethook.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c2724d986fa0..2fe24bbca618 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -106,6 +106,7 @@ config ARM
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI
 	select HAVE_OPTPROBES if !THUMB2_KERNEL
+	select HAVE_RETHOOK
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index 75e905508f27..3c2a9d7024bc 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 #include <linux/export.h>
 #include <linux/kprobes.h>
+#include <linux/rethook.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/stacktrace.h>
@@ -66,6 +67,9 @@ int notrace unwind_frame(struct stackframe *frame)
 	frame->sp = *(unsigned long *)(fp - 8);
 	frame->pc = *(unsigned long *)(fp - 4);
 #endif
+	if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(frame->pc))
+		frame->pc = rethook_find_ret_addr(frame->tsk, frame->fp,
+						  &frame->kr_cur);
 #ifdef CONFIG_KRETPROBES
 	if (is_kretprobe_trampoline(frame->pc))
 		frame->pc = kretprobe_find_ret_addr(frame->tsk,
diff --git a/arch/arm/probes/Makefile b/arch/arm/probes/Makefile
index 8b0ea5ace100..10c083a22223 100644
--- a/arch/arm/probes/Makefile
+++ b/arch/arm/probes/Makefile
@@ -6,3 +6,4 @@ obj-$(CONFIG_KPROBES)		+= decode-thumb.o
 else
 obj-$(CONFIG_KPROBES)		+= decode-arm.o
 endif
+obj-$(CONFIG_RETHOOK)		+= rethook.o
diff --git a/arch/arm/probes/rethook.c b/arch/arm/probes/rethook.c
new file mode 100644
index 000000000000..adc16cdf358a
--- /dev/null
+++ b/arch/arm/probes/rethook.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * arm implementation of rethook. Mostly copied from arch/arm/probes/kprobes/core.c
+ */
+
+#include <linux/kprobes.h>
+#include <linux/rethook.h>
+
+/* Called from arch_rethook_trampoline */
+static __used unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs)
+{
+	return rethook_trampoline_handler(regs, regs->ARM_fp);
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
+
+/*
+ * When a rethook'ed function returns, it returns to arch_rethook_trampoline
+ * which calls rethook callback. We construct a struct pt_regs to
+ * give a view of registers r0-r11, sp, lr, and pc to the user
+ * return-handler. This is not a complete pt_regs structure, but that
+ * should be enough for stacktrace from the return handler with or
+ * without pt_regs.
+ */
+void __naked arch_rethook_trampoline(void)
+{
+	__asm__ __volatile__ (
+#ifdef CONFIG_FRAME_POINTER
+		"ldr	lr, =arch_rethook_trampoline	\n\t"
+	/* this makes a framepointer on pt_regs. */
+#ifdef CONFIG_CC_IS_CLANG
+		"stmdb	sp, {sp, lr, pc}	\n\t"
+		"sub	sp, sp, #12		\n\t"
+		/* In clang case, pt_regs->ip = lr. */
+		"stmdb	sp!, {r0 - r11, lr}	\n\t"
+		/* fp points regs->r11 (fp) */
+		"add	fp, sp,	#44		\n\t"
+#else /* !CONFIG_CC_IS_CLANG */
+		/* In gcc case, pt_regs->ip = fp. */
+		"stmdb	sp, {fp, sp, lr, pc}	\n\t"
+		"sub	sp, sp, #16		\n\t"
+		"stmdb	sp!, {r0 - r11}		\n\t"
+		/* fp points regs->r15 (pc) */
+		"add	fp, sp, #60		\n\t"
+#endif /* CONFIG_CC_IS_CLANG */
+#else /* !CONFIG_FRAME_POINTER */
+		"sub	sp, sp, #16		\n\t"
+		"stmdb	sp!, {r0 - r11}		\n\t"
+#endif /* CONFIG_FRAME_POINTER */
+		"mov	r0, sp			\n\t"
+		"bl	arch_rethook_trampoline_callback	\n\t"
+		"mov	lr, r0			\n\t"
+		"ldmia	sp!, {r0 - r11}		\n\t"
+		"add	sp, sp, #16		\n\t"
+#ifdef CONFIG_THUMB2_KERNEL
+		"bx	lr			\n\t"
+#else
+		"mov	pc, lr			\n\t"
+#endif
+		: : : "memory");
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline);
+
+void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs)
+{
+	rh->ret_addr = regs->ARM_lr;
+	rh->frame = regs->ARM_fp;
+
+	/* Replace the return addr with trampoline addr. */
+	regs->ARM_lr = (unsigned long)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare);

[PATCH v4 6/9] arm64: rethook: Add arm64 rethook implementation

[Masami Hiramatsu]

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 arch/arm64/Kconfig                            |    1 
 arch/arm64/kernel/probes/Makefile             |    1 
 arch/arm64/kernel/probes/rethook.c            |   25 +++++++
 arch/arm64/kernel/probes/rethook_trampoline.S |   87 +++++++++++++++++++++++++
 arch/arm64/kernel/stacktrace.c                |    3 +
 5 files changed, 117 insertions(+)
 create mode 100644 arch/arm64/kernel/probes/rethook.c
 create mode 100644 arch/arm64/kernel/probes/rethook_trampoline.S

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c4207cf9bb17..c706ed25ea50 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -201,6 +201,7 @@ config ARM64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
+	select HAVE_RETHOOK
 	select HAVE_GENERIC_VDSO
 	select IOMMU_DMA if IOMMU_SUPPORT
 	select IRQ_DOMAIN
diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
index 8e4be92e25b1..24e689f44c32 100644
--- a/arch/arm64/kernel/probes/Makefile
+++ b/arch/arm64/kernel/probes/Makefile
@@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o	\
 				   simulate-insn.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o	\
 				   simulate-insn.o
+obj-$(CONFIG_RETHOOK)		+= rethook.o rethook_trampoline.o
diff --git a/arch/arm64/kernel/probes/rethook.c b/arch/arm64/kernel/probes/rethook.c
new file mode 100644
index 000000000000..38c33c81438b
--- /dev/null
+++ b/arch/arm64/kernel/probes/rethook.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Generic return hook for arm64.
+ * Most of the code is copied from arch/arm64/kernel/probes/kprobes.c
+ */
+
+#include <linux/kprobes.h>
+#include <linux/rethook.h>
+
+/* This is called from arch_rethook_trampoline() */
+unsigned long __used arch_rethook_trampoline_callback(struct pt_regs *regs)
+{
+	return rethook_trampoline_handler(regs, regs->regs[29]);
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
+
+void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs)
+{
+	rhn->ret_addr = regs->regs[30];
+	rhn->frame = regs->regs[29];
+
+	/* replace return addr (x30) with trampoline */
+	regs->regs[30] = (u64)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare);
diff --git a/arch/arm64/kernel/probes/rethook_trampoline.S b/arch/arm64/kernel/probes/rethook_trampoline.S
new file mode 100644
index 000000000000..610f520ee72b
--- /dev/null
+++ b/arch/arm64/kernel/probes/rethook_trampoline.S
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * trampoline entry and return code for rethook.
+ * Copied from arch/arm64/kernel/probes/kprobes_trampoline.S
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/assembler.h>
+
+	.text
+
+	.macro	save_all_base_regs
+	stp x0, x1, [sp, #S_X0]
+	stp x2, x3, [sp, #S_X2]
+	stp x4, x5, [sp, #S_X4]
+	stp x6, x7, [sp, #S_X6]
+	stp x8, x9, [sp, #S_X8]
+	stp x10, x11, [sp, #S_X10]
+	stp x12, x13, [sp, #S_X12]
+	stp x14, x15, [sp, #S_X14]
+	stp x16, x17, [sp, #S_X16]
+	stp x18, x19, [sp, #S_X18]
+	stp x20, x21, [sp, #S_X20]
+	stp x22, x23, [sp, #S_X22]
+	stp x24, x25, [sp, #S_X24]
+	stp x26, x27, [sp, #S_X26]
+	stp x28, x29, [sp, #S_X28]
+	add x0, sp, #PT_REGS_SIZE
+	stp lr, x0, [sp, #S_LR]
+	/*
+	 * Construct a useful saved PSTATE
+	 */
+	mrs x0, nzcv
+	mrs x1, daif
+	orr x0, x0, x1
+	mrs x1, CurrentEL
+	orr x0, x0, x1
+	mrs x1, SPSel
+	orr x0, x0, x1
+	stp xzr, x0, [sp, #S_PC]
+	.endm
+
+	.macro	restore_all_base_regs
+	ldr x0, [sp, #S_PSTATE]
+	and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
+	msr nzcv, x0
+	ldp x0, x1, [sp, #S_X0]
+	ldp x2, x3, [sp, #S_X2]
+	ldp x4, x5, [sp, #S_X4]
+	ldp x6, x7, [sp, #S_X6]
+	ldp x8, x9, [sp, #S_X8]
+	ldp x10, x11, [sp, #S_X10]
+	ldp x12, x13, [sp, #S_X12]
+	ldp x14, x15, [sp, #S_X14]
+	ldp x16, x17, [sp, #S_X16]
+	ldp x18, x19, [sp, #S_X18]
+	ldp x20, x21, [sp, #S_X20]
+	ldp x22, x23, [sp, #S_X22]
+	ldp x24, x25, [sp, #S_X24]
+	ldp x26, x27, [sp, #S_X26]
+	ldp x28, x29, [sp, #S_X28]
+	.endm
+
+SYM_CODE_START(arch_rethook_trampoline)
+	sub sp, sp, #PT_REGS_SIZE
+
+	save_all_base_regs
+
+	/* Setup a frame pointer. */
+	add x29, sp, #S_FP
+
+	mov x0, sp
+	bl arch_rethook_trampoline_callback
+	/*
+	 * Replace trampoline address in lr with actual orig_ret_addr return
+	 * address.
+	 */
+	mov lr, x0
+
+	/* The frame pointer (x29) is restored with other registers. */
+	restore_all_base_regs
+
+	add sp, sp, #PT_REGS_SIZE
+	ret
+
+SYM_CODE_END(arch_rethook_trampoline)
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index b0f21677764d..d0883d0fa61c 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -8,6 +8,7 @@
 #include <linux/export.h>
 #include <linux/ftrace.h>
 #include <linux/kprobes.h>
+#include <linux/rethook.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
@@ -137,6 +138,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 	if (is_kretprobe_trampoline(frame->pc))
 		frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
 #endif
+	if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(frame->pc))
+		frame->pc = rethook_find_ret_addr(tsk, frame->fp, &frame->kr_cur);
 
 	return 0;
 }

[PATCH v4 7/9] fprobe: Add exit_handler support

[Masami Hiramatsu]

Add exit_handler to fprobe. fprobe + rethook allows us
to hook the kernel function return without fgraph tracer.
Eventually, the fgraph tracer will be generic array based
return hooking and fprobe may use it if user requests.
Since both array-based approach and list-based approach
have Pros and Cons, (e.g. memory consumption v.s. less
missing events) it is better to keep both but fprobe
will provide the same exit-handler interface.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v4:
  - Check fprobe is disabled in the exit handler.
 Changes in v3:
  - Make sure to clear rethook->data before free.
  - Handler checks the data is not NULL.
  - Free rethook only if the rethook is using.
---
 include/linux/fprobe.h |    6 ++++
 kernel/trace/Kconfig   |    1 +
 kernel/trace/fprobe.c  |   65 +++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
index f7de332b08c2..4692089b9118 100644
--- a/include/linux/fprobe.h
+++ b/include/linux/fprobe.h
@@ -5,6 +5,7 @@
 
 #include <linux/compiler.h>
 #include <linux/ftrace.h>
+#include <linux/rethook.h>
 
 /**
  * struct fprobe - ftrace based probe.
@@ -14,7 +15,9 @@
  * @ops: The ftrace_ops.
  * @nmissed: The counter for missing events.
  * @flags: The status flag.
+ * @rethook: The rethook data structure. (internal data)
  * @entry_handler: The callback function for function entry.
+ * @exit_handler: The callback function for function exit.
  *
  * User must set either @syms or @addrs, but not both. If user sets
  * only @syms, the @addrs are generated when registering the fprobe.
@@ -28,7 +31,10 @@ struct fprobe {
 	struct ftrace_ops	ops;
 	unsigned long		nmissed;
 	unsigned int		flags;
+	struct rethook		*rethook;
+
 	void (*entry_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
+	void (*exit_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
 };
 
 #define FPROBE_FL_DISABLED	1
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 4d27e56c6e76..6176904c4741 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -238,6 +238,7 @@ config FPROBE
 	bool "Kernel Function Probe (fprobe)"
 	depends on FUNCTION_TRACER
 	depends on DYNAMIC_FTRACE_WITH_REGS
+	select RETHOOK
 	default n
 	help
 	  This option enables kernel function probe (fprobe) based on ftrace,
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 748cc34765c1..4d089dda89c2 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -7,12 +7,20 @@
 #include <linux/fprobe.h>
 #include <linux/kallsyms.h>
 #include <linux/kprobes.h>
+#include <linux/rethook.h>
 #include <linux/slab.h>
 #include <linux/sort.h>
 
+struct fprobe_rethook_node {
+	struct rethook_node node;
+	unsigned long entry_ip;
+};
+
 static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
 			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
 {
+	struct fprobe_rethook_node *fpr;
+	struct rethook_node *rh;
 	struct fprobe *fp;
 	int bit;
 
@@ -29,10 +37,37 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
 	if (fp->entry_handler)
 		fp->entry_handler(fp, ip, ftrace_get_regs(fregs));
 
+	if (fp->exit_handler) {
+		rh = rethook_try_get(fp->rethook);
+		if (!rh) {
+			fp->nmissed++;
+			goto out;
+		}
+		fpr = container_of(rh, struct fprobe_rethook_node, node);
+		fpr->entry_ip = ip;
+		rethook_hook(rh, ftrace_get_regs(fregs));
+	}
+
+out:
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(fprobe_handler);
 
+static void fprobe_exit_handler(struct rethook_node *rh, void *data,
+				struct pt_regs *regs)
+{
+	struct fprobe *fp = (struct fprobe *)data;
+	struct fprobe_rethook_node *fpr;
+
+	if (!fp || fprobe_disabled(fp))
+		return;
+
+	fpr = container_of(rh, struct fprobe_rethook_node, node);
+
+	fp->exit_handler(fp, fpr->entry_ip, regs);
+}
+NOKPROBE_SYMBOL(fprobe_exit_handler);
+
 /* Convert ftrace location address from symbols */
 static int convert_func_addresses(struct fprobe *fp)
 {
@@ -82,6 +117,7 @@ static int convert_func_addresses(struct fprobe *fp)
  */
 int register_fprobe(struct fprobe *fp)
 {
+	unsigned int i, size;
 	int ret;
 
 	if (!fp || !fp->nentry || (!fp->syms && !fp->addrs) ||
@@ -96,10 +132,29 @@ int register_fprobe(struct fprobe *fp)
 	fp->ops.func = fprobe_handler;
 	fp->ops.flags = FTRACE_OPS_FL_SAVE_REGS;
 
+	/* Initialize rethook if needed */
+	if (fp->exit_handler) {
+		size = fp->nentry * num_possible_cpus() * 2;
+		fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
+		for (i = 0; i < size; i++) {
+			struct rethook_node *node;
+
+			node = kzalloc(sizeof(struct fprobe_rethook_node), GFP_KERNEL);
+			if (!node) {
+				rethook_free(fp->rethook);
+				ret = -ENOMEM;
+				goto out;
+			}
+			rethook_add_node(fp->rethook, node);
+		}
+	} else
+		fp->rethook = NULL;
+
 	ret = ftrace_set_filter_ips(&fp->ops, fp->addrs, fp->nentry, 0, 0);
 	if (!ret)
 		ret = register_ftrace_function(&fp->ops);
 
+out:
 	if (ret < 0 && fp->syms) {
 		kfree(fp->addrs);
 		fp->addrs = NULL;
@@ -125,8 +180,16 @@ int unregister_fprobe(struct fprobe *fp)
 		return -EINVAL;
 
 	ret = unregister_ftrace_function(&fp->ops);
+	if (ret < 0)
+		return ret;
 
-	if (!ret && fp->syms) {
+	if (fp->rethook) {
+		/* Make sure to clear rethook->data before freeing. */
+		WRITE_ONCE(fp->rethook->data, NULL);
+		barrier();
+		rethook_free(fp->rethook);
+	}
+	if (fp->syms) {
 		kfree(fp->addrs);
 		fp->addrs = NULL;
 	}

[PATCH v4 8/9] fprobe: Add sample program for fprobe

[Masami Hiramatsu]

Add a sample program for the fprobe.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v2:
  - Fix infinit loop for multiple symbols.
  - Fix memory leaks for copied string and entry array.
  - Update for new fprobe APIs.
  - Fix style issues.
---
 samples/Kconfig                 |    7 +++
 samples/Makefile                |    1 
 samples/fprobe/Makefile         |    3 +
 samples/fprobe/fprobe_example.c |  103 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 114 insertions(+)
 create mode 100644 samples/fprobe/Makefile
 create mode 100644 samples/fprobe/fprobe_example.c

diff --git a/samples/Kconfig b/samples/Kconfig
index 43d2e9aa557f..e010c2c1256c 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -73,6 +73,13 @@ config SAMPLE_HW_BREAKPOINT
 	help
 	  This builds kernel hardware breakpoint example modules.
 
+config SAMPLE_FPROBE
+	tristate "Build fprobe examples -- loadable modules only"
+	depends on FPROBE && m
+	help
+	  This builds a fprobe example module. This module has an option 'symbol'.
+	  You can specify a probed symbol or symbols separated with ','.
+
 config SAMPLE_KFIFO
 	tristate "Build kfifo examples -- loadable modules only"
 	depends on m
diff --git a/samples/Makefile b/samples/Makefile
index 4bcd6b93bffa..4f73fe7aa473 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -32,3 +32,4 @@ obj-$(CONFIG_SAMPLE_INTEL_MEI)		+= mei/
 subdir-$(CONFIG_SAMPLE_WATCHDOG)	+= watchdog
 subdir-$(CONFIG_SAMPLE_WATCH_QUEUE)	+= watch_queue
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST)	+= kmemleak/
+obj-$(CONFIG_SAMPLE_FPROBE)		+= fprobe/
diff --git a/samples/fprobe/Makefile b/samples/fprobe/Makefile
new file mode 100644
index 000000000000..ecccbfa6e99b
--- /dev/null
+++ b/samples/fprobe/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_SAMPLE_FPROBE) += fprobe_example.o
diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
new file mode 100644
index 000000000000..c28320537f98
--- /dev/null
+++ b/samples/fprobe/fprobe_example.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Here's a sample kernel module showing the use of fprobe to dump a
+ * stack trace and selected registers when kernel_clone() is called.
+ *
+ * For more information on theory of operation of kprobes, see
+ * Documentation/trace/kprobes.rst
+ *
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever kernel_clone() is invoked to create a new process.
+ */
+
+#define pr_fmt(fmt) "%s: " fmt, __func__
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/fprobe.h>
+#include <linux/slab.h>
+
+#define MAX_SYMBOL_LEN 4096
+struct fprobe sample_probe;
+static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
+module_param_string(symbol, symbol, sizeof(symbol), 0644);
+
+static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
+{
+	pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+}
+
+static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
+{
+	unsigned long rip = instruction_pointer(regs);
+
+	pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
+		(void *)ip, (void *)ip, (void *)rip, (void *)rip);
+}
+
+static char *symbuf;
+
+static int __init fprobe_init(void)
+{
+	const char **syms;
+	char *p;
+	int ret, count, i;
+
+	sample_probe.entry_handler = sample_entry_handler;
+	sample_probe.exit_handler = sample_exit_handler;
+
+	if (strchr(symbol, ',')) {
+		symbuf = kstrdup(symbol, GFP_KERNEL);
+		if (!symbuf)
+			return -ENOMEM;
+		p = symbuf;
+		count = 1;
+		while ((p = strchr(++p, ',')) != NULL)
+			count++;
+	} else {
+		count = 1;
+		symbuf = symbol;
+	}
+	pr_info("%d symbols found\n", count);
+
+	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
+	if (!syms) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	p = symbuf;
+	for (i = 0; i < count; i++)
+		syms[i] = strsep(&p, ",");
+
+	sample_probe.syms = syms;
+	sample_probe.nentry = count;
+
+	ret = register_fprobe(&sample_probe);
+	if (ret < 0) {
+		pr_err("register_fprobe failed, returned %d\n", ret);
+		goto error;
+	}
+	pr_info("Planted fprobe at %s\n", symbol);
+	return 0;
+
+error:
+	if (symbuf != symbol)
+		kfree(symbuf);
+	return ret;
+}
+
+static void __exit fprobe_exit(void)
+{
+	unregister_fprobe(&sample_probe);
+
+	kfree(sample_probe.syms);
+	if (symbuf != symbol)
+		kfree(symbuf);
+
+	pr_info("fprobe at %s unregistered\n", symbol);
+}
+
+module_init(fprobe_init)
+module_exit(fprobe_exit)
+MODULE_LICENSE("GPL");

[PATCH v4 9/9] docs: fprobe: Add fprobe description to ftrace-use.rst

[Masami Hiramatsu]

Add a documentation of fprobe for the user who needs
this interface.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Documentation/trace/fprobe.rst |  131 ++++++++++++++++++++++++++++++++++++++++
 Documentation/trace/index.rst  |    1 
 2 files changed, 132 insertions(+)
 create mode 100644 Documentation/trace/fprobe.rst

diff --git a/Documentation/trace/fprobe.rst b/Documentation/trace/fprobe.rst
new file mode 100644
index 000000000000..c53950a1f91e
--- /dev/null
+++ b/Documentation/trace/fprobe.rst
@@ -0,0 +1,131 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
+Fprobe - Function entry/exit probe
+==================================
+
+.. Author: Masami Hiramatsu <mhiramat@kernel.org>
+
+Introduction
+============
+
+Instead of using ftrace full feature, if you only want to attach callbacks
+on function entry and exit, similar to the kprobes and kretprobes, you can
+use fprobe. Compared with kprobes and kretprobes, fprobe gives faster
+instrumentation for multiple functions with single handler. This document
+describes how to use fprobe.
+
+The usage of fprobe
+===================
+
+The fprobe is a wrapper of ftrace (+ kretprobe-like return callback) to
+attach callbacks to multiple function entry and exit. User needs to set up
+the `struct fprobe` and pass it to `register_fprobe()`.
+
+Typically, `fprobe` data structure is initialized with the `syms`, `nentry`
+and `entry_handler` and/or `exit_handler` as below.
+
+.. code-block:: c
+
+ char targets[] = {"func1", "func2", "func3"};
+ struct fprobe fp = {
+        .syms           = targets,
+        .nentry         = ARRAY_SIZE(targets),
+        .entry_handler  = my_entry_callback,
+        .exit_handler   = my_exit_callback,
+ };
+
+The ftrace_ops in the fprobe is automatically set. The FTRACE_OPS_FL_SAVE_REGS
+and FTRACE_OPS_FL_RECURSION
+flag will be set. If you need other flags, please set it by yourself.
+
+.. code-block:: c
+
+ fp.ops.flags |= FTRACE_OPS_FL_RCU;
+
+To enable this fprobe, call::
+
+  register_fprobe(&fp);
+
+To disable (remove from functions) this fprobe, call::
+
+  unregister_fprobe(&fp);
+
+You can temporally (soft) disable the fprobe by::
+
+  disable_fprobe(&fp);
+
+and resume by::
+
+  enable_fprobe(&fp);
+
+The above is defined by including the header::
+
+  #include <linux/fprobe.h>
+
+Same as ftrace, the registered callback will start being called some time
+after the register_fprobe() is called and before it returns. See
+:file:`Documentation/trace/ftrace.rst`.
+
+
+The fprobe entry/exit handler
+=============================
+
+The prototype of the entry/exit callback function is as follows:
+
+.. code-block:: c
+
+ void callback_func(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
+
+Note that both entry and exit callback has same ptototype. The @entry_ip is
+saved at function entry and passed to exit handler.
+
+@fp
+        This is the address of `fprobe` data structure related to this handler.
+        You can embed the `fprobe` to your data structure and get it by
+        container_of() macro from @fp. The @fp must not be NULL.
+
+@entry_ip
+        This is the entry address of the traced function (both entry and exit).
+
+@regs
+        This is the `pt_regs` data structure at the entry and exit. Note that
+        the instruction pointer of @regs may be different from the @entry_ip
+        in the entry_handler. If you need traced instruction pointer, you need
+        to use @entry_ip. On the other hand, in the exit_handler, the instruction
+        pointer of @regs is set to the currect return address.
+
+
+Use fprobe with raw address list
+================================
+
+Instead of passing the array of symbols, you can pass a array of raw
+function addresses via `fprobe::addrs`. In this case, the value of
+this array will be changed automatically to the dynamic ftrace NOP
+location addresses in the given kernel function. So please take care
+if you share this array with others.
+
+
+The missed counter
+==================
+
+The `fprobe` data structure has `fprobe::nmissed` counter field as same as
+kprobes.
+This counter counts up when;
+
+ - fprobe fails to take ftrace_recursion lock. This usually means that a function
+   which is traced by other ftrace users is called from the entry_handler.
+
+ - fprobe fails to setup the function exit because of the shortage of rethook
+   (the shadow stack for hooking the function return.)
+
+Note that `fprobe::nmissed` field is counted up in both case. The former case
+will skip both of entry and exit callback, and the latter case will skip exit
+callback, but in both case the counter is just increased by 1.
+
+Functions and structures
+========================
+
+.. kernel-doc:: include/linux/fprobe.h
+.. kernel-doc:: kernel/trace/fprobe.c
+
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 3769b9b7aed8..b9f3757f8269 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -9,6 +9,7 @@ Linux Tracing Technologies
    tracepoint-analysis
    ftrace
    ftrace-uses
+   fprobe
    kprobes
    kprobetrace
    uprobetracer

Re: [PATCH v4 5/9] ARM: rethook: Add rethook arm implementation

[kernel test robot]

Hi Masami,

I love your patch! Yet something to improve:

[auto build test ERROR on rostedt-trace/for-next]
[also build test ERROR on arm64/for-next/core tip/x86/core linus/master v5.17-rc1 next-20220124]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next
config: arm-aspeed_g5_defconfig (https://download.01.org/0day-ci/archive/20220125/202201250328.drn6ia3n-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/df6df88bb474db78d80fc5619d39b25ec15d5d16
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
        git checkout df6df88bb474db78d80fc5619d39b25ec15d5d16
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm SHELL=/bin/bash arch/arm/kernel/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   arch/arm/kernel/stacktrace.c: In function 'unwind_frame':
>> arch/arm/kernel/stacktrace.c:71:56: error: 'struct stackframe' has no member named 'tsk'
      71 |                 frame->pc = rethook_find_ret_addr(frame->tsk, frame->fp,
         |                                                        ^~
>> arch/arm/kernel/stacktrace.c:72:57: error: 'struct stackframe' has no member named 'kr_cur'
      72 |                                                   &frame->kr_cur);
         |                                                         ^~


vim +71 arch/arm/kernel/stacktrace.c

    12	
    13	#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
    14	/*
    15	 * Unwind the current stack frame and store the new register values in the
    16	 * structure passed as argument. Unwinding is equivalent to a function return,
    17	 * hence the new PC value rather than LR should be used for backtrace.
    18	 *
    19	 * With framepointer enabled, a simple function prologue looks like this:
    20	 *	mov	ip, sp
    21	 *	stmdb	sp!, {fp, ip, lr, pc}
    22	 *	sub	fp, ip, #4
    23	 *
    24	 * A simple function epilogue looks like this:
    25	 *	ldm	sp, {fp, sp, pc}
    26	 *
    27	 * When compiled with clang, pc and sp are not pushed. A simple function
    28	 * prologue looks like this when built with clang:
    29	 *
    30	 *	stmdb	{..., fp, lr}
    31	 *	add	fp, sp, #x
    32	 *	sub	sp, sp, #y
    33	 *
    34	 * A simple function epilogue looks like this when built with clang:
    35	 *
    36	 *	sub	sp, fp, #x
    37	 *	ldm	{..., fp, pc}
    38	 *
    39	 *
    40	 * Note that with framepointer enabled, even the leaf functions have the same
    41	 * prologue and epilogue, therefore we can ignore the LR value in this case.
    42	 */
    43	int notrace unwind_frame(struct stackframe *frame)
    44	{
    45		unsigned long high, low;
    46		unsigned long fp = frame->fp;
    47	
    48		/* only go to a higher address on the stack */
    49		low = frame->sp;
    50		high = ALIGN(low, THREAD_SIZE);
    51	
    52	#ifdef CONFIG_CC_IS_CLANG
    53		/* check current frame pointer is within bounds */
    54		if (fp < low + 4 || fp > high - 4)
    55			return -EINVAL;
    56	
    57		frame->sp = frame->fp;
    58		frame->fp = *(unsigned long *)(fp);
    59		frame->pc = *(unsigned long *)(fp + 4);
    60	#else
    61		/* check current frame pointer is within bounds */
    62		if (fp < low + 12 || fp > high - 4)
    63			return -EINVAL;
    64	
    65		/* restore the registers from the stack frame */
    66		frame->fp = *(unsigned long *)(fp - 12);
    67		frame->sp = *(unsigned long *)(fp - 8);
    68		frame->pc = *(unsigned long *)(fp - 4);
    69	#endif
    70		if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(frame->pc))
  > 71			frame->pc = rethook_find_ret_addr(frame->tsk, frame->fp,
  > 72							  &frame->kr_cur);
    73	#ifdef CONFIG_KRETPROBES
    74		if (is_kretprobe_trampoline(frame->pc))
    75			frame->pc = kretprobe_find_ret_addr(frame->tsk,
    76						(void *)frame->fp, &frame->kr_cur);
    77	#endif
    78	
    79		return 0;
    80	}
    81	#endif
    82	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH v4 6/9] arm64: rethook: Add arm64 rethook implementation

[kernel test robot]

Hi Masami,

I love your patch! Yet something to improve:

[auto build test ERROR on rostedt-trace/for-next]
[also build test ERROR on arm64/for-next/core tip/x86/core linus/master v5.17-rc1 next-20220124]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next
config: arm64-randconfig-r033-20220124 (https://download.01.org/0day-ci/archive/20220125/202201250403.5YnZvb4K-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/981b0378461c912ba2d7b10412dd6fe21c316055
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
        git checkout 981b0378461c912ba2d7b10412dd6fe21c316055
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm64 SHELL=/bin/bash arch/arm64/kernel/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   arch/arm64/kernel/stacktrace.c: In function 'unwind_frame':
>> arch/arm64/kernel/stacktrace.c:141:73: error: 'struct stackframe' has no member named 'kr_cur'
     141 |                 frame->pc = rethook_find_ret_addr(tsk, frame->fp, &frame->kr_cur);
         |                                                                         ^~


vim +141 arch/arm64/kernel/stacktrace.c

    59	
    60	/*
    61	 * Unwind from one frame record (A) to the next frame record (B).
    62	 *
    63	 * We terminate early if the location of B indicates a malformed chain of frame
    64	 * records (e.g. a cycle), determined based on the location and fp value of A
    65	 * and the location (but not the fp value) of B.
    66	 */
    67	int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
    68	{
    69		unsigned long fp = frame->fp;
    70		struct stack_info info;
    71	
    72		if (!tsk)
    73			tsk = current;
    74	
    75		/* Final frame; nothing to unwind */
    76		if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
    77			return -ENOENT;
    78	
    79		if (fp & 0x7)
    80			return -EINVAL;
    81	
    82		if (!on_accessible_stack(tsk, fp, 16, &info))
    83			return -EINVAL;
    84	
    85		if (test_bit(info.type, frame->stacks_done))
    86			return -EINVAL;
    87	
    88		/*
    89		 * As stacks grow downward, any valid record on the same stack must be
    90		 * at a strictly higher address than the prior record.
    91		 *
    92		 * Stacks can nest in several valid orders, e.g.
    93		 *
    94		 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
    95		 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
    96		 *
    97		 * ... but the nesting itself is strict. Once we transition from one
    98		 * stack to another, it's never valid to unwind back to that first
    99		 * stack.
   100		 */
   101		if (info.type == frame->prev_type) {
   102			if (fp <= frame->prev_fp)
   103				return -EINVAL;
   104		} else {
   105			set_bit(frame->prev_type, frame->stacks_done);
   106		}
   107	
   108		/*
   109		 * Record this frame record's values and location. The prev_fp and
   110		 * prev_type are only meaningful to the next unwind_frame() invocation.
   111		 */
   112		frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
   113		frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
   114		frame->prev_fp = fp;
   115		frame->prev_type = info.type;
   116	
   117		frame->pc = ptrauth_strip_insn_pac(frame->pc);
   118	
   119	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
   120		if (tsk->ret_stack &&
   121			(frame->pc == (unsigned long)return_to_handler)) {
   122			unsigned long orig_pc;
   123			/*
   124			 * This is a case where function graph tracer has
   125			 * modified a return address (LR) in a stack frame
   126			 * to hook a function return.
   127			 * So replace it to an original value.
   128			 */
   129			orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc,
   130							(void *)frame->fp);
   131			if (WARN_ON_ONCE(frame->pc == orig_pc))
   132				return -EINVAL;
   133			frame->pc = orig_pc;
   134		}
   135	#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
   136	#ifdef CONFIG_KRETPROBES
   137		if (is_kretprobe_trampoline(frame->pc))
   138			frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
   139	#endif
   140		if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(frame->pc))
 > 141			frame->pc = rethook_find_ret_addr(tsk, frame->fp, &frame->kr_cur);
   142	
   143		return 0;
   144	}
   145	NOKPROBE_SYMBOL(unwind_frame);
   146	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH v4 4/9] rethook: x86: Add rethook x86 implementation

[kernel test robot]

Hi Masami,

I love your patch! Yet something to improve:

[auto build test ERROR on rostedt-trace/for-next]
[also build test ERROR on tip/x86/core linus/master v5.17-rc1 next-20220124]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next
config: i386-tinyconfig (https://download.01.org/0day-ci/archive/20220125/202201250509.MSbKNePn-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/6366c7f830e71242dd9538fbdb09acdccea6e786
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Masami-Hiramatsu/fprobe-Introduce-fprobe-function-entry-exit-probe/20220125-001253
        git checkout 6366c7f830e71242dd9538fbdb09acdccea6e786
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/kernel/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   In file included from arch/x86/kernel/process.c:48:
   arch/x86/include/asm/unwind.h: In function 'unwind_recover_kretprobe':
>> arch/x86/include/asm/unwind.h:113:17: error: 'struct unwind_state' has no member named 'kr_cur'
     113 |           &state->kr_cur);
         |                 ^~
   arch/x86/kernel/process.c: At top level:
   arch/x86/kernel/process.c:887:13: warning: no previous prototype for 'arch_post_acpi_subsys_init' [-Wmissing-prototypes]
     887 | void __init arch_post_acpi_subsys_init(void)
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~
--
   In file included from arch/x86/kernel/unwind_guess.c:7:
   arch/x86/include/asm/unwind.h: In function 'unwind_recover_kretprobe':
>> arch/x86/include/asm/unwind.h:113:17: error: 'struct unwind_state' has no member named 'kr_cur'
     113 |           &state->kr_cur);
         |                 ^~


vim +113 arch/x86/include/asm/unwind.h

   106	
   107	static inline
   108	unsigned long unwind_recover_kretprobe(struct unwind_state *state,
   109					       unsigned long addr, unsigned long *addr_p)
   110	{
   111		if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(addr))
   112			return rethook_find_ret_addr(state->task, (unsigned long)addr_p,
 > 113						     &state->kr_cur);
   114	#ifdef CONFIG_KRETPROBES
   115		return is_kretprobe_trampoline(addr) ?
   116			kretprobe_find_ret_addr(state->task, addr_p, &state->kr_cur) :
   117			addr;
   118	#else
   119		return addr;
   120	#endif
   121	}
   122	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH v4 4/9] rethook: x86: Add rethook x86 implementation

[Masami Hiramatsu]

On Tue, 25 Jan 2022 01:10:09 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Add rethook for x86 implementation. Most of the code
> has been copied from kretprobes on x86.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  Changes in v4:
>   - fix stack backtrace as same as kretprobe does.
> ---
>  arch/x86/Kconfig              |    1 
>  arch/x86/include/asm/unwind.h |    4 +
>  arch/x86/kernel/Makefile      |    1 
>  arch/x86/kernel/rethook.c     |  115 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 121 insertions(+)
>  create mode 100644 arch/x86/kernel/rethook.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5c2ccb85f2ef..0a7d48a63787 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -219,6 +219,7 @@ config X86
>  	select HAVE_KPROBES_ON_FTRACE
>  	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_KRETPROBES
> +	select HAVE_RETHOOK
>  	select HAVE_KVM
>  	select HAVE_LIVEPATCH			if X86_64
>  	select HAVE_MIXED_BREAKPOINTS_REGS
> diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
> index 2a1f8734416d..9fe5f73f22f1 100644
> --- a/arch/x86/include/asm/unwind.h
> +++ b/arch/x86/include/asm/unwind.h
> @@ -5,6 +5,7 @@
>  #include <linux/sched.h>
>  #include <linux/ftrace.h>
>  #include <linux/kprobes.h>
> +#include <linux/rethook.h>
>  #include <asm/ptrace.h>
>  #include <asm/stacktrace.h>
>  
> @@ -107,6 +108,9 @@ static inline
>  unsigned long unwind_recover_kretprobe(struct unwind_state *state,
>  				       unsigned long addr, unsigned long *addr_p)
>  {
> +	if (IS_ENABLED(CONFIG_RETHOOK) && is_rethook_trampoline(addr))
> +		return rethook_find_ret_addr(state->task, (unsigned long)addr_p,
> +					     &state->kr_cur);

Hm, I found that this doesn't work since state->kr_cur is not defined when
CONFIG_KRETPROBES=n. Even if I define it with CONFIG_RETHOOK=y, if both
CONFIG_RETHOOK and CONFIG_KRETPROBES are 'n', the compiler caused a build
error. So I decided to use #ifdef here in the next version.

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>