Merge branch 'bpf: Speed up symbol resolving in kprobe multi link'

Jiri Olsa says:

====================

hi,
sending additional fix for symbol resolving in kprobe multi link
requested by Alexei and Andrii [1].

This speeds up bpftrace kprobe attachment, when using pure symbols
(3344 symbols) to attach:

Before:

  # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
  ...
  6.5681 +- 0.0225 seconds time elapsed  ( +-  0.34% )

After:

  # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
  ...
  0.5661 +- 0.0275 seconds time elapsed  ( +-  4.85% )

v6 changes:
  - rewrote patch 1 changelog and fixed the line length [Christoph]

v5 changes:
  - added acks [Masami]
  - workaround in selftest for RCU warning by filtering out several
    functions to attach

v4 changes:
  - fix compile issue [kernel test robot]
  - added acks [Andrii]

v3 changes:
  - renamed kallsyms_lookup_names to ftrace_lookup_symbols
    and moved it to ftrace.c [Masami]
  - added ack [Andrii]
  - couple small test fixes [Andrii]

v2 changes (first version [2]):
  - removed the 2 seconds check [Alexei]
  - moving/forcing symbols sorting out of kallsyms_lookup_names function [Alexei]
  - skipping one array allocation and copy_from_user [Andrii]
  - several small fixes [Masami,Andrii]
  - build fix [kernel test robot]

thanks,
jirka

[1] https://lore.kernel.org/bpf/CAEf4BzZtQaiUxQ-sm_hH2qKPRaqGHyOfEsW96DxtBHRaKLoL3Q@mail.gmail.com/
[2] https://lore.kernel.org/bpf/20220407125224.310255-1-jolsa@kernel.org/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/ftrace.h

@@ -303,6 +303,8 @@ int unregister_ftrace_function(struct ftrace_ops *ops);
 extern void ftrace_stub(unsigned long a0, unsigned long a1,
 			struct ftrace_ops *op, struct ftrace_regs *fregs);
 
+
+int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs);
 #else /* !CONFIG_FUNCTION_TRACER */
 /*
  * (un)register_ftrace_function must be a macro since the ops parameter
@@ -313,6 +315,10 @@ extern void ftrace_stub(unsigned long a0, unsigned long a1,
 static inline void ftrace_kill(void) { }
 static inline void ftrace_free_init_mem(void) { }
 static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
+static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_FUNCTION_TRACER */
 
 struct ftrace_func_entry {

include/linux/kallsyms.h

@@ -65,11 +65,11 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 	return ptr;
 }
 
+#ifdef CONFIG_KALLSYMS
 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 				      unsigned long),
 			    void *data);
 
-#ifdef CONFIG_KALLSYMS
 /* Lookup the address for a symbol. Returns 0 if not found. */
 unsigned long kallsyms_lookup_name(const char *name);
 
@@ -163,6 +163,11 @@ static inline bool kallsyms_show_value(const struct cred *cred)
 	return false;
 }
 
+static inline int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
+					  unsigned long), void *data)
+{
+	return -EOPNOTSUPP;
+}
 #endif /*CONFIG_KALLSYMS*/
 
 static inline void print_ip_sym(const char *loglvl, unsigned long ip)

kernel/kallsyms.c

@@ -29,6 +29,7 @@
 #include <linux/compiler.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/bsearch.h>
 
 /*
  * These will be re-linked against their real values
@@ -228,7 +229,6 @@ unsigned long kallsyms_lookup_name(const char *name)
 	return module_kallsyms_lookup_name(name);
 }
 
-#ifdef CONFIG_LIVEPATCH
 /*
  * Iterate over all symbols in vmlinux.  For symbols from modules use
  * module_kallsyms_on_each_symbol instead.
@@ -251,7 +251,6 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 	}
 	return 0;
 }
-#endif /* CONFIG_LIVEPATCH */
 
 static unsigned long get_symbol_pos(unsigned long addr,
 				    unsigned long *symbolsize,

kernel/trace/bpf_trace.c

@@ -2229,6 +2229,59 @@ struct bpf_kprobe_multi_run_ctx {
 	unsigned long entry_ip;
 };
 
+struct user_syms {
+	const char **syms;
+	char *buf;
+};
+
+static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
+{
+	unsigned long __user usymbol;
+	const char **syms = NULL;
+	char *buf = NULL, *p;
+	int err = -ENOMEM;
+	unsigned int i;
+
+	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
+	if (!syms)
+		goto error;
+
+	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
+	if (!buf)
+		goto error;
+
+	for (p = buf, i = 0; i < cnt; i++) {
+		if (__get_user(usymbol, usyms + i)) {
+			err = -EFAULT;
+			goto error;
+		}
+		err = strncpy_from_user(p, (const char __user *) usymbol, KSYM_NAME_LEN);
+		if (err == KSYM_NAME_LEN)
+			err = -E2BIG;
+		if (err < 0)
+			goto error;
+		syms[i] = p;
+		p += err + 1;
+	}
+
+	us->syms = syms;
+	us->buf = buf;
+	return 0;
+
+error:
+	if (err) {
+		kvfree(syms);
+		kvfree(buf);
+	}
+	return err;
+}
+
+static void free_user_syms(struct user_syms *us)
+{
+	kvfree(us->syms);
+	kvfree(us->buf);
+}
+
 static void bpf_kprobe_multi_link_release(struct bpf_link *link)
 {
 	struct bpf_kprobe_multi_link *kmulti_link;
@@ -2349,53 +2402,12 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
 	kprobe_multi_link_prog_run(link, entry_ip, regs);
 }
 
-static int
-kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
-			  unsigned long *addrs)
+static int symbols_cmp(const void *a, const void *b)
 {
-	unsigned long addr, size;
-	const char __user **syms;
-	int err = -ENOMEM;
-	unsigned int i;
-	char *func;
-
-	size = cnt * sizeof(*syms);
-	syms = kvzalloc(size, GFP_KERNEL);
-	if (!syms)
-		return -ENOMEM;
+	const char **str_a = (const char **) a;
+	const char **str_b = (const char **) b;
 
-	func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
-	if (!func)
-		goto error;
-
-	if (copy_from_user(syms, usyms, size)) {
-		err = -EFAULT;
-		goto error;
-	}
-
-	for (i = 0; i < cnt; i++) {
-		err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
-		if (err == KSYM_NAME_LEN)
-			err = -E2BIG;
-		if (err < 0)
-			goto error;
-		err = -EINVAL;
-		addr = kallsyms_lookup_name(func);
-		if (!addr)
-			goto error;
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
-			goto error;
-		addr = ftrace_location_range(addr, addr + size - 1);
-		if (!addr)
-			goto error;
-		addrs[i] = addr;
-	}
-
-	err = 0;
-error:
-	kvfree(syms);
-	kfree(func);
-	return err;
+	return strcmp(*str_a, *str_b);
 }
 
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
@@ -2441,7 +2453,15 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 			goto error;
 		}
 	} else {
-		err = kprobe_multi_resolve_syms(usyms, cnt, addrs);
+		struct user_syms us;
+
+		err = copy_user_syms(&us, usyms, cnt);
+		if (err)
+			goto error;
+
+		sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
+		err = ftrace_lookup_symbols(us.syms, cnt, addrs);
+		free_user_syms(&us);
 		if (err)
 			goto error;
 	}

kernel/trace/fprobe.c

@@ -85,39 +85,31 @@ static void fprobe_exit_handler(struct rethook_node *rh, void *data,
 }
 NOKPROBE_SYMBOL(fprobe_exit_handler);
 
+static int symbols_cmp(const void *a, const void *b)
+{
+	const char **str_a = (const char **) a;
+	const char **str_b = (const char **) b;
+
+	return strcmp(*str_a, *str_b);
+}
+
 /* Convert ftrace location address from symbols */
 static unsigned long *get_ftrace_locations(const char **syms, int num)
 {
-	unsigned long addr, size;
 	unsigned long *addrs;
-	int i;
 
 	/* Convert symbols to symbol address */
 	addrs = kcalloc(num, sizeof(*addrs), GFP_KERNEL);
 	if (!addrs)
 		return ERR_PTR(-ENOMEM);
 
-	for (i = 0; i < num; i++) {
-		addr = kallsyms_lookup_name(syms[i]);
-		if (!addr)	/* Maybe wrong symbol */
-			goto error;
-
-		/* Convert symbol address to ftrace location. */
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL) || !size)
-			goto error;
+	/* ftrace_lookup_symbols expects sorted symbols */
+	sort(syms, num, sizeof(*syms), symbols_cmp, NULL);
 
-		addr = ftrace_location_range(addr, addr + size - 1);
-		if (!addr) /* No dynamic ftrace there. */
-			goto error;
+	if (!ftrace_lookup_symbols(syms, num, addrs))
+		return addrs;
 
-		addrs[i] = addr;
-	}
-
-	return addrs;
-
-error:
 	kfree(addrs);
-
 	return ERR_PTR(-ENOENT);
 }
 

kernel/trace/ftrace.c

@@ -7964,3 +7964,65 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 	mutex_unlock(&ftrace_lock);
 	return ret;
 }
+
+static int symbols_cmp(const void *a, const void *b)
+{
+	const char **str_a = (const char **) a;
+	const char **str_b = (const char **) b;
+
+	return strcmp(*str_a, *str_b);
+}
+
+struct kallsyms_data {
+	unsigned long *addrs;
+	const char **syms;
+	size_t cnt;
+	size_t found;
+};
+
+static int kallsyms_callback(void *data, const char *name,
+			     struct module *mod, unsigned long addr)
+{
+	struct kallsyms_data *args = data;
+
+	if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
+		return 0;
+
+	addr = ftrace_location(addr);
+	if (!addr)
+		return 0;
+
+	args->addrs[args->found++] = addr;
+	return args->found == args->cnt ? 1 : 0;
+}
+
+/**
+ * ftrace_lookup_symbols - Lookup addresses for array of symbols
+ *
+ * @sorted_syms: array of symbols pointers symbols to resolve,
+ * must be alphabetically sorted
+ * @cnt: number of symbols/addresses in @syms/@addrs arrays
+ * @addrs: array for storing resulting addresses
+ *
+ * This function looks up addresses for array of symbols provided in
+ * @syms array (must be alphabetically sorted) and stores them in
+ * @addrs array, which needs to be big enough to store at least @cnt
+ * addresses.
+ *
+ * This function returns 0 if all provided symbols are found,
+ * -ESRCH otherwise.
+ */
+int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
+{
+	struct kallsyms_data args;
+	int err;
+
+	args.addrs = addrs;
+	args.syms = sorted_syms;
+	args.cnt = cnt;
+	args.found = 0;
+	err = kallsyms_on_each_symbol(kallsyms_callback, &args);
+	if (err < 0)
+		return err;
+	return args.found == args.cnt ? 0 : -ESRCH;
+}