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bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link 

Using kallsyms_lookup_names function to speed up symbols lookup in
kprobe multi link attachment and replacing with it the current
kprobe_multi_resolve_syms function.

This speeds up bpftrace kprobe attachment:

  # 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% )

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220510122616.2652285-5-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jiri Olsa 2022-05-10 14:26:15 +02:00 committed by Alexei Starovoitov
parent 8be9253344
commit 0236fec57a
1 changed files with 66 additions and 46 deletions
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112
kernel/trace/bpf_trace.c
View File

@ -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;
const char **str_a = (const char **) a;
const char **str_b = (const char **) b;
size = cnt * sizeof(*syms);
syms = kvzalloc(size, GFP_KERNEL);
if (!syms)
return -ENOMEM;
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;
}