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bpf: Support ->fill_link_info for perf_event
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By introducing support for ->fill_link_info to the perf_event link, users
gain the ability to inspect it using `bpftool link show`. While the current
approach involves accessing this information via `bpftool perf show`,
consolidating link information for all link types in one place offers
greater convenience. Additionally, this patch extends support to the
generic perf event, which is not currently accommodated by
`bpftool perf show`. While only the perf type and config are exposed to
userspace, other attributes such as sample_period and sample_freq are
ignored. It's important to note that if kptr_restrict is not permitted, the
probed address will not be exposed, maintaining security measures.

A new enum bpf_perf_event_type is introduced to help the user understand
which struct is relevant.

Signed-off-by: Yafang Shao <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
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@laoar
laoar authored and Alexei Starovoitov committed Jul 12, 2023
1 parent 57d4853 commit 1b715e1
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Showing 4 changed files with 223 additions and 3 deletions.
35 changes: 35 additions & 0 deletions include/uapi/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1057,6 +1057,16 @@ enum bpf_link_type {
MAX_BPF_LINK_TYPE,
};

enum bpf_perf_event_type {
BPF_PERF_EVENT_UNSPEC = 0,
BPF_PERF_EVENT_UPROBE = 1,
BPF_PERF_EVENT_URETPROBE = 2,
BPF_PERF_EVENT_KPROBE = 3,
BPF_PERF_EVENT_KRETPROBE = 4,
BPF_PERF_EVENT_TRACEPOINT = 5,
BPF_PERF_EVENT_EVENT = 6,
};

/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
*
* NONE(default): No further bpf programs allowed in the subtree.
Expand Down Expand Up @@ -6444,6 +6454,31 @@ struct bpf_link_info {
__u32 count; /* in/out: kprobe_multi function count */
__u32 flags;
} kprobe_multi;
struct {
__u32 type; /* enum bpf_perf_event_type */
__u32 :32;
union {
struct {
__aligned_u64 file_name; /* in/out */
__u32 name_len;
__u32 offset; /* offset from file_name */
} uprobe; /* BPF_PERF_EVENT_UPROBE, BPF_PERF_EVENT_URETPROBE */
struct {
__aligned_u64 func_name; /* in/out */
__u32 name_len;
__u32 offset; /* offset from func_name */
__u64 addr;
} kprobe; /* BPF_PERF_EVENT_KPROBE, BPF_PERF_EVENT_KRETPROBE */
struct {
__aligned_u64 tp_name; /* in/out */
__u32 name_len;
} tracepoint; /* BPF_PERF_EVENT_TRACEPOINT */
struct {
__u64 config;
__u32 type;
} event; /* BPF_PERF_EVENT_EVENT */
};
} perf_event;
};
} __attribute__((aligned(8)));

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146 changes: 146 additions & 0 deletions kernel/bpf/syscall.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3364,9 +3364,155 @@ static void bpf_perf_link_dealloc(struct bpf_link *link)
kfree(perf_link);
}

static int bpf_perf_link_fill_common(const struct perf_event *event,
char __user *uname, u32 ulen,
u64 *probe_offset, u64 *probe_addr,
u32 *fd_type)
{
const char *buf;
u32 prog_id;
size_t len;
int err;

if (!ulen ^ !uname)
return -EINVAL;
if (!uname)
return 0;

err = bpf_get_perf_event_info(event, &prog_id, fd_type, &buf,
probe_offset, probe_addr);
if (err)
return err;

if (buf) {
len = strlen(buf);
err = bpf_copy_to_user(uname, buf, ulen, len);
if (err)
return err;
} else {
char zero = '\0';

if (put_user(zero, uname))
return -EFAULT;
}
return 0;
}

#ifdef CONFIG_KPROBE_EVENTS
static int bpf_perf_link_fill_kprobe(const struct perf_event *event,
struct bpf_link_info *info)
{
char __user *uname;
u64 addr, offset;
u32 ulen, type;
int err;

uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
ulen = info->perf_event.kprobe.name_len;
err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
&type);
if (err)
return err;
if (type == BPF_FD_TYPE_KRETPROBE)
info->perf_event.type = BPF_PERF_EVENT_KRETPROBE;
else
info->perf_event.type = BPF_PERF_EVENT_KPROBE;

info->perf_event.kprobe.offset = offset;
if (!kallsyms_show_value(current_cred()))
addr = 0;
info->perf_event.kprobe.addr = addr;
return 0;
}
#endif

#ifdef CONFIG_UPROBE_EVENTS
static int bpf_perf_link_fill_uprobe(const struct perf_event *event,
struct bpf_link_info *info)
{
char __user *uname;
u64 addr, offset;
u32 ulen, type;
int err;

uname = u64_to_user_ptr(info->perf_event.uprobe.file_name);
ulen = info->perf_event.uprobe.name_len;
err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
&type);
if (err)
return err;

if (type == BPF_FD_TYPE_URETPROBE)
info->perf_event.type = BPF_PERF_EVENT_URETPROBE;
else
info->perf_event.type = BPF_PERF_EVENT_UPROBE;
info->perf_event.uprobe.offset = offset;
return 0;
}
#endif

static int bpf_perf_link_fill_probe(const struct perf_event *event,
struct bpf_link_info *info)
{
#ifdef CONFIG_KPROBE_EVENTS
if (event->tp_event->flags & TRACE_EVENT_FL_KPROBE)
return bpf_perf_link_fill_kprobe(event, info);
#endif
#ifdef CONFIG_UPROBE_EVENTS
if (event->tp_event->flags & TRACE_EVENT_FL_UPROBE)
return bpf_perf_link_fill_uprobe(event, info);
#endif
return -EOPNOTSUPP;
}

static int bpf_perf_link_fill_tracepoint(const struct perf_event *event,
struct bpf_link_info *info)
{
char __user *uname;
u32 ulen;

uname = u64_to_user_ptr(info->perf_event.tracepoint.tp_name);
ulen = info->perf_event.tracepoint.name_len;
info->perf_event.type = BPF_PERF_EVENT_TRACEPOINT;
return bpf_perf_link_fill_common(event, uname, ulen, NULL, NULL, NULL);
}

static int bpf_perf_link_fill_perf_event(const struct perf_event *event,
struct bpf_link_info *info)
{
info->perf_event.event.type = event->attr.type;
info->perf_event.event.config = event->attr.config;
info->perf_event.type = BPF_PERF_EVENT_EVENT;
return 0;
}

static int bpf_perf_link_fill_link_info(const struct bpf_link *link,
struct bpf_link_info *info)
{
struct bpf_perf_link *perf_link;
const struct perf_event *event;

perf_link = container_of(link, struct bpf_perf_link, link);
event = perf_get_event(perf_link->perf_file);
if (IS_ERR(event))
return PTR_ERR(event);

switch (event->prog->type) {
case BPF_PROG_TYPE_PERF_EVENT:
return bpf_perf_link_fill_perf_event(event, info);
case BPF_PROG_TYPE_TRACEPOINT:
return bpf_perf_link_fill_tracepoint(event, info);
case BPF_PROG_TYPE_KPROBE:
return bpf_perf_link_fill_probe(event, info);
default:
return -EOPNOTSUPP;
}
}

static const struct bpf_link_ops bpf_perf_link_lops = {
.release = bpf_perf_link_release,
.dealloc = bpf_perf_link_dealloc,
.fill_link_info = bpf_perf_link_fill_link_info,
};

static int bpf_perf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
Expand Down
10 changes: 7 additions & 3 deletions kernel/trace/bpf_trace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2369,9 +2369,13 @@ int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
if (is_tracepoint || is_syscall_tp) {
*buf = is_tracepoint ? event->tp_event->tp->name
: event->tp_event->name;
*fd_type = BPF_FD_TYPE_TRACEPOINT;
*probe_offset = 0x0;
*probe_addr = 0x0;
/* We allow NULL pointer for tracepoint */
if (fd_type)
*fd_type = BPF_FD_TYPE_TRACEPOINT;
if (probe_offset)
*probe_offset = 0x0;
if (probe_addr)
*probe_addr = 0x0;
} else {
/* kprobe/uprobe */
err = -EOPNOTSUPP;
Expand Down
35 changes: 35 additions & 0 deletions tools/include/uapi/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1057,6 +1057,16 @@ enum bpf_link_type {
MAX_BPF_LINK_TYPE,
};

enum bpf_perf_event_type {
BPF_PERF_EVENT_UNSPEC = 0,
BPF_PERF_EVENT_UPROBE = 1,
BPF_PERF_EVENT_URETPROBE = 2,
BPF_PERF_EVENT_KPROBE = 3,
BPF_PERF_EVENT_KRETPROBE = 4,
BPF_PERF_EVENT_TRACEPOINT = 5,
BPF_PERF_EVENT_EVENT = 6,
};

/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
*
* NONE(default): No further bpf programs allowed in the subtree.
Expand Down Expand Up @@ -6444,6 +6454,31 @@ struct bpf_link_info {
__u32 count; /* in/out: kprobe_multi function count */
__u32 flags;
} kprobe_multi;
struct {
__u32 type; /* enum bpf_perf_event_type */
__u32 :32;
union {
struct {
__aligned_u64 file_name; /* in/out */
__u32 name_len;
__u32 offset; /* offset from file_name */
} uprobe; /* BPF_PERF_EVENT_UPROBE, BPF_PERF_EVENT_URETPROBE */
struct {
__aligned_u64 func_name; /* in/out */
__u32 name_len;
__u32 offset; /* offset from func_name */
__u64 addr;
} kprobe; /* BPF_PERF_EVENT_KPROBE, BPF_PERF_EVENT_KRETPROBE */
struct {
__aligned_u64 tp_name; /* in/out */
__u32 name_len;
} tracepoint; /* BPF_PERF_EVENT_TRACEPOINT */
struct {
__u64 config;
__u32 type;
} event; /* BPF_PERF_EVENT_EVENT */
};
} perf_event;
};
} __attribute__((aligned(8)));

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