Re: [PATCH bpf-next v3 4/4] bpf_trace: pass array of u64 values in kprobe_multi.addrs

On 5/17/22 1:03 PM, Jiri Olsa wrote:

On Tue, May 17, 2022 at 02:30:50PM +0200, Eugene Syromiatnikov wrote:

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On Tue, May 17, 2022 at 11:12:34AM +0200, Jiri Olsa wrote:

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On Tue, May 17, 2022 at 09:36:47AM +0200, Eugene Syromiatnikov wrote:

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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 ABI to accept an array of u64 values instead of (kernel? user?) longs. Interestingly, the rest of the libbpf infrastructure uses 64-bit values for kallsyms addresses already, so this patch also eliminates the sym_addr cast in tools/lib/bpf/libbpf.c:resolve_kprobe_multi_cb().

so the problem is when we have 32bit user sace on 64bit kernel right?

I think we should keep addrs as longs in uapi and have kernel to figure out if it needs to read u32 or u64, like you did for symbols in previous patch

No, it's not possible here, as addrs are kernel addrs and not user space addrs, so user space has to explicitly pass 64-bit addresses on 64-bit kernels (or have a notion whether it is running on a 64-bit or 32-bit kernel, and form the passed array accordingly, which is against the idea of compat layer that tries to abstract it out).

hum :-\ I'll need to check on compat layer.. there must be some other code doing this already somewhere, right?

I am not familiar with all these compatibility thing. But if we have 64-bit pointer for **syms, maybe we could also have 64-bit pointer for *syms for consistency?

jirka

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we'll need to fix also bpf_kprobe_multi_cookie_swap because it assumes 64bit user space pointers

would be gret if we could have selftest for this

thanks, jirka

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Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link") 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

---

kernel/trace/bpf_trace.c | 25 ++++++++++++++++++---- tools/lib/bpf/bpf.h | 2 +- tools/lib/bpf/libbpf.c | 8 +++---- tools/lib/bpf/libbpf.h | 2 +- .../testing/selftests/bpf/prog_tests/bpf_cookie.c | 2 +- .../selftests/bpf/prog_tests/kprobe_multi_test.c | 8 +++---- 6 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 9d3028a..30a15b3 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2454,7 +2454,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr void __user *ucookies; unsigned long *addrs; u32 flags, cnt, size, cookies_size;

• void __user *uaddrs;

• u64 __user *uaddrs; u64 *cookies = NULL; void __user *usyms; int err;

@@ -2486,9 +2486,26 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr return -ENOMEM; if (uaddrs) {

• if (copy_from_user(addrs, uaddrs, size)) {
  

• 	err = -EFAULT;
  

• 	goto error;
  

• if (sizeof(*addrs) == sizeof(*uaddrs)) {
  

• 	if (copy_from_user(addrs, uaddrs, size)) {
  

• 		err = -EFAULT;
  

• 		goto error;
  

• 	}
  

• } else {
  

• 	u32 i;
  

• 	u64 addr;
  

• 	for (i = 0; i < cnt; i++) {
  

• 		if (get_user(addr, uaddrs + i)) {
  

• 			err = -EFAULT;
  

• 			goto error;
  

• 		}
  

• 		if (addr > ULONG_MAX) {
  

• 			err = -EINVAL;
  

• 			goto error;
  

• 		}
  

• 		addrs[i] = addr;
  

• 	}
  

  } } else { struct user_syms us;

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h index 2e0d373..da9c6037 100644 --- a/tools/lib/bpf/bpf.h +++ b/tools/lib/bpf/bpf.h @@ -418,7 +418,7 @@ struct bpf_link_create_opts { __u32 flags; __u32 cnt; const char **syms;

• 	const unsigned long *addrs;
  

• 	const __u64 *addrs;
  const __u64 *cookies;
  

  } kprobe_multi; struct {

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index ef7f302..35fa9c5 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -10737,7 +10737,7 @@ 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; };

@@ -10752,12 +10752,12 @@ 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; }

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