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

From: Jiri Olsa <[email-masked]>
Date: Thu, 19 May 2022 22:15:12 +0200

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 <[email-masked]>
> > ---
> >   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;