[PATCH v2 bpf-next 0/3] libbpf: uprobe name-based attach followups

[PATCH v2 bpf-next 0/3] libbpf: uprobe name-based attach followups

[Alan Maguire]

Follow-up series to [1] to address some suggestions from Andrii to
improve parsing and make it more robust (patches 1, 2) and to improve
validation of u[ret]probe firing by validating expected argument
and return values (patch 3).

[1] https://lore.kernel.org/bpf/164903521182.13106.12656654142629368774.git-patchwork-notify@kernel.org/

Changes since v1:
- split library name, auto-attach parsing into separate patches (Andrii, patches 1, 2)
- made str_has_sfx() static inline, avoided repeated strlen()s by storing lengths,
  used strlen() instead of strnlen() (Andrii, patch 1)
- fixed sscanf() arg to use %li, switched logging to use "prog '%s'" format,
  used direct strcmp() on probe_type instead of prefix check (Andrii, patch 2)
- switched auto-attach tests to log parameter/return values to be checked by
  user-space side of tests. Needed to add pid filtering to avoid capturing
  stray malloc()s (Andrii, patch 3) 

Alan Maguire (3):
  libbpf: improve library identification for uprobe binary path
    resolution
  libbpf: improve string parsing for uprobe auto-attach
  selftests/bpf: uprobe tests should verify param/return values

 tools/lib/bpf/libbpf.c                             | 85 +++++++++-------------
 tools/lib/bpf/libbpf_internal.h                    | 11 +++
 .../selftests/bpf/prog_tests/uprobe_autoattach.c   | 25 +++++--
 .../selftests/bpf/progs/test_uprobe_autoattach.c   | 43 ++++++++---
 4 files changed, 96 insertions(+), 68 deletions(-)

-- 
1.8.3.1

[PATCH v2 bpf-next 1/3] libbpf: improve library identification for uprobe binary path resolution

[Alan Maguire]

In the process of doing path resolution for uprobe attach, libraries are
identified by matching a ".so" substring in the binary_path.
This matches a lot of patterns that do not conform to library.so[.version]
format, so instead match a ".so" _suffix_, and if that fails match a
".so." substring for the versioned library case.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/libbpf.c          |  2 +-
 tools/lib/bpf/libbpf_internal.h | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 1111e9d..c92226a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10766,7 +10766,7 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 	const char *search_paths[3] = {};
 	int i;
 
-	if (strstr(file, ".so")) {
+	if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
 		search_paths[0] = getenv("LD_LIBRARY_PATH");
 		search_paths[1] = "/usr/lib64:/usr/lib";
 		search_paths[2] = arch_specific_lib_paths();
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index dd0d4cc..0802724 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -103,6 +103,17 @@
 #define str_has_pfx(str, pfx) \
 	(strncmp(str, pfx, __builtin_constant_p(pfx) ? sizeof(pfx) - 1 : strlen(pfx)) == 0)
 
+/* suffix check */
+static inline bool str_has_sfx(const char *str, const char *sfx)
+{
+	size_t str_len = strlen(str);
+	size_t sfx_len = strlen(sfx);
+
+	if (sfx_len <= str_len)
+		return strcmp(str + str_len - sfx_len, sfx);
+	return false;
+}
+
 /* Symbol versioning is different between static and shared library.
  * Properly versioned symbols are needed for shared library, but
  * only the symbol of the new version is needed for static library.
-- 
1.8.3.1

[PATCH v2 bpf-next 2/3] libbpf: improve string parsing for uprobe auto-attach

[Alan Maguire]

For uprobe auto-attach, the parsing can be simplified for the SEC()
name to a single sscanf(); the return value of the sscanf can then
be used to distinguish between sections that simply specify
"u[ret]probe" (and thus cannot auto-attach), those that specify
"u[ret]probe/binary_path:function+offset" etc.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/libbpf.c | 83 +++++++++++++++++++++-----------------------------
 1 file changed, 34 insertions(+), 49 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c92226a..707dcc3 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10913,60 +10913,45 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
 {
 	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
-	char *func, *probe_name, *func_end;
-	char *func_name, binary_path[512];
-	unsigned long long raw_offset;
-	size_t offset = 0;
-	int n;
+	char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
+	int n, ret = -EINVAL;
+	long offset = 0;
 
 	*link = NULL;
 
-	opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
-	if (opts.retprobe)
-		probe_name = prog->sec_name + sizeof("uretprobe") - 1;
-	else
-		probe_name = prog->sec_name + sizeof("uprobe") - 1;
-	if (probe_name[0] == '/')
-		probe_name++;
-
-	/* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
-	if (strlen(probe_name) == 0)
-		return 0;
-
-	snprintf(binary_path, sizeof(binary_path), "%s", probe_name);
-	/* ':' should be prior to function+offset */
-	func_name = strrchr(binary_path, ':');
-	if (!func_name) {
-		pr_warn("section '%s' missing ':function[+offset]' specification\n",
-			prog->sec_name);
-		return -EINVAL;
-	}
-	func_name[0] = '\0';
-	func_name++;
-	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
-	if (n < 1) {
-		pr_warn("uprobe name '%s' is invalid\n", func_name);
-		return -EINVAL;
-	}
-	if (opts.retprobe && offset != 0) {
-		free(func);
-		pr_warn("uretprobes do not support offset specification\n");
-		return -EINVAL;
-	}
-
-	/* Is func a raw address? */
-	errno = 0;
-	raw_offset = strtoull(func, &func_end, 0);
-	if (!errno && !*func_end) {
-		free(func);
-		func = NULL;
-		offset = (size_t)raw_offset;
+	n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li",
+		   &probe_type, &binary_path, &func_name, &offset);
+	switch (n) {
+	case 1:
+		/* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
+		ret = 0;
+		break;
+	case 2:
+		pr_warn("prog '%s': section '%s' missing ':function[+offset]' specification\n",
+			prog->name, prog->sec_name);
+		break;
+	case 3:
+	case 4:
+		opts.retprobe = strcmp(probe_type, "uretprobe") == 0;
+		if (opts.retprobe && offset != 0) {
+			pr_warn("prog '%s': uretprobes do not support offset specification\n",
+				prog->name);
+			break;
+		}
+		opts.func_name = func_name;
+		*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
+		ret = libbpf_get_error(*link);
+		break;
+	default:
+		pr_warn("prog '%s': invalid format of section definition '%s'\n", prog->name,
+			prog->sec_name);
+		break;
 	}
-	opts.func_name = func;
+	free(probe_type);
+	free(binary_path);
+	free(func_name);
 
-	*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
-	free(func);
-	return libbpf_get_error(*link);
+	return ret;
 }
 
 struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
-- 
1.8.3.1

[PATCH v2 bpf-next 3/3] selftests/bpf: uprobe tests should verify param/return values

[Alan Maguire]

uprobe/uretprobe tests don't do any validation of arguments/return values,
and without this we can't be sure we are attached to the right function,
or that we are indeed attached to a uprobe or uretprobe.  To fix this
record argument and return value for auto-attached functions and ensure
these match expectations.  Also need to filter by pid to ensure we do
not pick up stray malloc()s since auto-attach traces libc system-wide.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 .../selftests/bpf/prog_tests/uprobe_autoattach.c   | 25 +++++++++----
 .../selftests/bpf/progs/test_uprobe_autoattach.c   | 43 ++++++++++++++++------
 2 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c b/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
index 03b15d6..d6003dc 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c
@@ -5,14 +5,17 @@
 #include "test_uprobe_autoattach.skel.h"
 
 /* uprobe attach point */
-static void autoattach_trigger_func(void)
+static noinline int autoattach_trigger_func(int arg)
 {
 	asm volatile ("");
+	return arg + 1;
 }
 
 void test_uprobe_autoattach(void)
 {
 	struct test_uprobe_autoattach *skel;
+	int trigger_val = 100, trigger_ret;
+	size_t malloc_sz = 1;
 	char *mem;
 
 	skel = test_uprobe_autoattach__open_and_load();
@@ -22,17 +25,25 @@ void test_uprobe_autoattach(void)
 	if (!ASSERT_OK(test_uprobe_autoattach__attach(skel), "skel_attach"))
 		goto cleanup;
 
+	skel->bss->test_pid = getpid();
+
 	/* trigger & validate uprobe & uretprobe */
-	autoattach_trigger_func();
+	trigger_ret = autoattach_trigger_func(trigger_val);
+
+	skel->bss->test_pid = getpid();
 
 	/* trigger & validate shared library u[ret]probes attached by name */
-	mem = malloc(1);
+	mem = malloc(malloc_sz);
 	free(mem);
 
-	ASSERT_EQ(skel->bss->uprobe_byname_res, 1, "check_uprobe_byname_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname_res, 2, "check_uretprobe_byname_res");
-	ASSERT_EQ(skel->bss->uprobe_byname2_res, 3, "check_uprobe_byname2_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname2_res, 4, "check_uretprobe_byname2_res");
+	ASSERT_EQ(skel->bss->uprobe_byname_parm1, trigger_val, "check_uprobe_byname_parm1");
+	ASSERT_EQ(skel->bss->uprobe_byname_ran, 1, "check_uprobe_byname_ran");
+	ASSERT_EQ(skel->bss->uretprobe_byname_rc, trigger_ret, "check_uretprobe_byname_rc");
+	ASSERT_EQ(skel->bss->uretprobe_byname_ran, 2, "check_uretprobe_byname_ran");
+	ASSERT_EQ(skel->bss->uprobe_byname2_parm1, malloc_sz, "check_uprobe_byname2_parm1");
+	ASSERT_EQ(skel->bss->uprobe_byname2_ran, 3, "check_uprobe_byname2_ran");
+	ASSERT_EQ(skel->bss->uretprobe_byname2_rc, mem, "check_uretprobe_byname2_rc");
+	ASSERT_EQ(skel->bss->uretprobe_byname2_ran, 4, "check_uretprobe_byname2_ran");
 cleanup:
 	test_uprobe_autoattach__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/test_uprobe_autoattach.c b/tools/testing/selftests/bpf/progs/test_uprobe_autoattach.c
index b442fb5..ab75522 100644
--- a/tools/testing/selftests/bpf/progs/test_uprobe_autoattach.c
+++ b/tools/testing/selftests/bpf/progs/test_uprobe_autoattach.c
@@ -1,15 +1,22 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2022, Oracle and/or its affiliates. */
 
-#include <linux/ptrace.h>
-#include <linux/bpf.h>
+#include "vmlinux.h"
+
+#include <bpf/bpf_core_read.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
-int uprobe_byname_res = 0;
-int uretprobe_byname_res = 0;
-int uprobe_byname2_res = 0;
-int uretprobe_byname2_res = 0;
+int uprobe_byname_parm1 = 0;
+int uprobe_byname_ran = 0;
+int uretprobe_byname_rc = 0;
+int uretprobe_byname_ran = 0;
+size_t uprobe_byname2_parm1 = 0;
+int uprobe_byname2_ran = 0;
+char *uretprobe_byname2_rc = NULL;
+int uretprobe_byname2_ran = 0;
+
+int test_pid;
 
 /* This program cannot auto-attach, but that should not stop other
  * programs from attaching.
@@ -23,14 +30,16 @@ int handle_uprobe_noautoattach(struct pt_regs *ctx)
 SEC("uprobe//proc/self/exe:autoattach_trigger_func")
 int handle_uprobe_byname(struct pt_regs *ctx)
 {
-	uprobe_byname_res = 1;
+	uprobe_byname_parm1 = PT_REGS_PARM1_CORE(ctx);
+	uprobe_byname_ran = 1;
 	return 0;
 }
 
 SEC("uretprobe//proc/self/exe:autoattach_trigger_func")
 int handle_uretprobe_byname(struct pt_regs *ctx)
 {
-	uretprobe_byname_res = 2;
+	uretprobe_byname_rc = PT_REGS_RC_CORE(ctx);
+	uretprobe_byname_ran = 2;
 	return 0;
 }
 
@@ -38,14 +47,26 @@ int handle_uretprobe_byname(struct pt_regs *ctx)
 SEC("uprobe/libc.so.6:malloc")
 int handle_uprobe_byname2(struct pt_regs *ctx)
 {
-	uprobe_byname2_res = 3;
+	int pid = bpf_get_current_pid_tgid() >> 32;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid)
+		return 0;
+	uprobe_byname2_parm1 = PT_REGS_PARM1_CORE(ctx);
+	uprobe_byname2_ran = 3;
 	return 0;
 }
 
-SEC("uretprobe/libc.so.6:free")
+SEC("uretprobe/libc.so.6:malloc")
 int handle_uretprobe_byname2(struct pt_regs *ctx)
 {
-	uretprobe_byname2_res = 4;
+	int pid = bpf_get_current_pid_tgid() >> 32;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid)
+		return 0;
+	uretprobe_byname2_rc = (char *)PT_REGS_RC_CORE(ctx);
+	uretprobe_byname2_ran = 4;
 	return 0;
 }
 
-- 
1.8.3.1

Re: [PATCH v2 bpf-next 0/3] libbpf: uprobe name-based attach followups

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed,  6 Apr 2022 12:43:48 +0100 you wrote:
> Follow-up series to [1] to address some suggestions from Andrii to
> improve parsing and make it more robust (patches 1, 2) and to improve
> validation of u[ret]probe firing by validating expected argument
> and return values (patch 3).
> 
> [1] https://lore.kernel.org/bpf/164903521182.13106.12656654142629368774.git-patchwork-notify@kernel.org/
> 
> [...]

Here is the summary with links:
  - [v2,bpf-next,1/3] libbpf: improve library identification for uprobe binary path resolution
    https://git.kernel.org/bpf/bpf-next/c/a1c9d61b19cb
  - [v2,bpf-next,2/3] libbpf: improve string parsing for uprobe auto-attach
    https://git.kernel.org/bpf/bpf-next/c/90db26e6be01
  - [v2,bpf-next,3/3] selftests/bpf: uprobe tests should verify param/return values
    https://git.kernel.org/bpf/bpf-next/c/1717e248014c

You are awesome, thank you!
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