Re: [PATCH bpf v4 3/3] libbpf, selftests/bpf: pass array of u64 values in kprobe_multi.addrs

On Thu, May 19, 2022 at 12:43:18PM -0700, Yonghong Song wrote:

On 5/19/22 11:14 AM, Eugene Syromiatnikov wrote:

...

With the interface as defined, it is impossible to pass 64-bit kernel addresses from a 32-bit userspace process in BPF_LINK_TYPE_KPROBE_MULTI, which severly limits the useability of the interface, change the API to accept an array of u64 values instead of (kernel? user?) longs. This patch implements the user space part of the change (without the relevant kernel changes, since, as of now, an attempt to add kprobe_multi link will fail with -EOPNOTSUPP), to avoid changing the interface after a release.

Fixes: 5117c26e877352bc ("libbpf: Add bpf_link_create support for multi kprobes") Fixes: ddc6b04989eb0993 ("libbpf: Add bpf_program__attach_kprobe_multi_opts function") Fixes: f7a11eeccb111854 ("selftests/bpf: Add kprobe_multi attach test") Fixes: 9271a0c7ae7a9147 ("selftests/bpf: Add attach test for bpf_program__attach_kprobe_multi_opts") Fixes: 2c6401c966ae1fbe ("selftests/bpf: Add kprobe_multi bpf_cookie test") Signed-off-by: Eugene Syromiatnikov esyr@redhat.com

---

tools/lib/bpf/bpf.h | 2 +- tools/lib/bpf/libbpf.c | 8 ++++---- tools/lib/bpf/libbpf.h | 2 +- tools/testing/selftests/bpf/prog_tests/bpf_cookie.c | 2 +- tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 8 ++++---- 5 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h index f4b4afb..f677602 100644 --- a/tools/lib/bpf/bpf.h +++ b/tools/lib/bpf/bpf.h @@ -417,7 +417,7 @@ struct bpf_link_create_opts { __u32 flags; __u32 cnt; const char **syms;

• 	const unsigned long *addrs;
  

• 	const __u64 *addrs;
  

Patch 2 and 3 will prevent supporting 64-bit kernel, 32-bit userspace for kprobe_multi. So effectively, kprobe_multi only supports 64-bit kernel and 64-bit user space. This is definitely an option, but it would be great if other people can chime in as well for whether this choice is best or not.

IIUC patch 3 is preparation for kernel change that will enable 32 bit userspace and 64 bit kernel, and Eugene will send it later

sounds good to me

jirka

...

	const __u64 *cookies;
} kprobe_multi;

}; diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 809fe20..03a14a6 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -10279,7 +10279,7 @@ static bool glob_match(const char *str, const char *pat) struct kprobe_multi_resolve { const char *pattern;

• unsigned long *addrs;

• __u64 *addrs; size_t cap; size_t cnt; };

@@ -10294,12 +10294,12 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, if (!glob_match(sym_name, res->pattern)) return 0;

• err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),

• err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(__u64), res->cnt + 1); if (err) return err;

• res->addrs[res->cnt++] = (unsigned long) sym_addr;

• res->addrs[res->cnt++] = sym_addr; return 0; }

@@ -10314,7 +10314,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, }; struct bpf_link *link = NULL; char errmsg[STRERR_BUFSIZE];

• const unsigned long *addrs;

• const __u64 *addrs; int err, link_fd, prog_fd; const __u64 *cookies; const char **syms;

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 05dde85..ec1cb61 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -431,7 +431,7 @@ struct bpf_kprobe_multi_opts { /* array of function symbols to attach */ const char **syms; /* array of function addresses to attach */

• const unsigned long *addrs;

• const __u64 *addrs; /* array of user-provided values fetchable through bpf_get_attach_cookie */ const __u64 *cookies; /* number of elements in syms/addrs/cookies arrays */

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c index 923a613..5aa482a 100644 --- a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c +++ b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c @@ -137,7 +137,7 @@ static void kprobe_multi_link_api_subtest(void) cookies[6] = 7; cookies[7] = 8;

• opts.kprobe_multi.addrs = (const unsigned long *) &addrs;

• opts.kprobe_multi.addrs = (const __u64 *) &addrs; opts.kprobe_multi.cnt = ARRAY_SIZE(addrs); opts.kprobe_multi.cookies = (const __u64 *) &cookies; prog_fd = bpf_program__fd(skel->progs.test_kprobe);

diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c index b9876b5..fbf4cf2 100644 --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c @@ -105,7 +105,7 @@ static void test_link_api_addrs(void) GET_ADDR("bpf_fentry_test7", addrs[6]); GET_ADDR("bpf_fentry_test8", addrs[7]);

• opts.kprobe_multi.addrs = (const unsigned long*) addrs;

• opts.kprobe_multi.addrs = (const __u64 *) addrs; opts.kprobe_multi.cnt = ARRAY_SIZE(addrs); test_link_api(&opts); }

@@ -183,7 +183,7 @@ static void test_attach_api_addrs(void) GET_ADDR("bpf_fentry_test7", addrs[6]); GET_ADDR("bpf_fentry_test8", addrs[7]);

• opts.addrs = (const unsigned long *) addrs;

• opts.addrs = (const __u64 *) addrs; opts.cnt = ARRAY_SIZE(addrs); test_attach_api(NULL, &opts); }

@@ -241,7 +241,7 @@ static void test_attach_api_fails(void) goto cleanup; /* fail_2 - both addrs and syms set */

• opts.addrs = (const unsigned long *) addrs;

• opts.addrs = (const __u64 *) addrs; opts.syms = syms; opts.cnt = ARRAY_SIZE(syms); opts.cookies = NULL;

@@ -255,7 +255,7 @@ static void test_attach_api_fails(void) goto cleanup; /* fail_3 - pattern and addrs set */

• opts.addrs = (const unsigned long *) addrs;

• opts.addrs = (const __u64 *) addrs; opts.syms = NULL; opts.cnt = ARRAY_SIZE(syms); opts.cookies = NULL;