[PATCH v3 bpf-next 2/4] bpf: introduce helper bpf_get_task_stack()

From: Song Liu
Date: Fri Jun 26 2020 - 20:29:20 EST

Introduce helper bpf_get_task_stack(), which dumps stack trace of given
task. This is different to bpf_get_stack(), which gets stack track of
current task. One potential use case of bpf_get_task_stack() is to call
it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.

bpf_get_task_stack() uses stack_trace_save_tsk() instead of
get_perf_callchain() for kernel stack. The benefit of this choice is that
stack_trace_save_tsk() doesn't require changes in arch/. The downside of
using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
stack trace to unsigned long array. For 32-bit systems, we need to
translate it to u64 array.

Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 36 +++++++++++++++-
kernel/bpf/stackmap.c | 75 ++++++++++++++++++++++++++++++++--
kernel/bpf/verifier.c | 4 +-
kernel/trace/bpf_trace.c | 2 +
scripts/bpf_helpers_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 36 +++++++++++++++-
7 files changed, 150 insertions(+), 6 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 3d2ade703a357..0cd7f6884c5cd 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1627,6 +1627,7 @@ extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
extern const struct bpf_func_proto bpf_get_current_comm_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto;
extern const struct bpf_func_proto bpf_get_stack_proto;
+extern const struct bpf_func_proto bpf_get_task_stack_proto;
extern const struct bpf_func_proto bpf_sock_map_update_proto;
extern const struct bpf_func_proto bpf_sock_hash_update_proto;
extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0cb8ec9488168..54106ea667211 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3285,6 +3285,39 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
* Return
* *sk* if casting is valid, or NULL otherwise.
+ *
+ * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
+ * Description
+ * Return a user or a kernel stack in bpf program provided buffer.
+ * To achieve this, the helper needs *task*, which is a valid
+ * pointer to struct task_struct. To store the stacktrace, the
+ * bpf program provides *buf* with a nonnegative *size*.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_USER_BUILD_ID**
+ * Collect buildid+offset instead of ips for user stack,
+ * only valid if **BPF_F_USER_STACK** is also specified.
+ *
+ * **bpf_get_task_stack**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
+ * to sufficient large buffer size. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * A non-negative value equal to or less than *size* on success,
+ * or a negative error in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3427,7 +3460,8 @@ union bpf_attr {
FN(skc_to_tcp_sock), \
FN(skc_to_tcp_timewait_sock), \
FN(skc_to_tcp_request_sock), \
- FN(skc_to_udp6_sock),
+ FN(skc_to_udp6_sock), \
+ FN(get_task_stack),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 27dc9b1b08a52..0ba66b29ef227 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -348,6 +348,40 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
}
}

+static struct perf_callchain_entry *
+get_callchain_entry_for_task(struct task_struct *task, u32 init_nr)
+{
+ struct perf_callchain_entry *entry;
+ int rctx;
+
+ entry = get_callchain_entry(&rctx);
+
+ if (!entry)
+ return NULL;
+
+ entry->nr = init_nr +
+ stack_trace_save_tsk(task, (unsigned long *)(entry->ip + init_nr),
+ sysctl_perf_event_max_stack - init_nr, 0);
+
+ /* stack_trace_save_tsk() works on unsigned long array, while
+ * perf_callchain_entry uses u64 array. For 32-bit systems, it is
+ * necessary to fix this mismatch.
+ */
+ if (__BITS_PER_LONG != 64) {
+ unsigned long *from = (unsigned long *) entry->ip;
+ u64 *to = entry->ip;
+ int i;
+
+ /* copy data from the end to avoid using extra buffer */
+ for (i = entry->nr - 1; i >= (int)init_nr; i--)
+ to[i] = (u64)(from[i]);
+ }
+
+ put_callchain_entry(rctx);
+
+ return entry;
+}
+
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u64, flags)
{
@@ -448,8 +482,8 @@ const struct bpf_func_proto bpf_get_stackid_proto = {
.arg3_type = ARG_ANYTHING,
};

-BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
- u64, flags)
+static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
+ void *buf, u32 size, u64 flags)
{
u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
@@ -471,13 +505,22 @@ BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
if (unlikely(size % elem_size))
goto clear;

+ /* cannot get valid user stack for task without user_mode regs */
+ if (task && user && !user_mode(regs))
+ goto err_fault;
+
num_elem = size / elem_size;
if (sysctl_perf_event_max_stack < num_elem)
init_nr = 0;
else
init_nr = sysctl_perf_event_max_stack - num_elem;
+
+ if (kernel && task)
+ trace = get_callchain_entry_for_task(task, init_nr);
+ else
trace = get_perf_callchain(regs, init_nr, kernel, user,
- sysctl_perf_event_max_stack, false, false);
+ sysctl_perf_event_max_stack,
+ false, false);
if (unlikely(!trace))
goto err_fault;

@@ -505,6 +548,12 @@ BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
return err;
}

+BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
+ u64, flags)
+{
+ return __bpf_get_stack(regs, NULL, buf, size, flags);
+}
+
const struct bpf_func_proto bpf_get_stack_proto = {
.func = bpf_get_stack,
.gpl_only = true,
@@ -515,6 +564,26 @@ const struct bpf_func_proto bpf_get_stack_proto = {
.arg4_type = ARG_ANYTHING,
};

+BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
+ u32, size, u64, flags)
+{
+ struct pt_regs *regs = task_pt_regs(task);
+
+ return __bpf_get_stack(regs, task, buf, size, flags);
+}
+
+static int bpf_get_task_stack_btf_ids[5];
+const struct bpf_func_proto bpf_get_task_stack_proto = {
+ .func = bpf_get_task_stack,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg2_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg3_type = ARG_CONST_SIZE_OR_ZERO,
+ .arg4_type = ARG_ANYTHING,
+ .btf_id = bpf_get_task_stack_btf_ids,
+};
+
/* Called from eBPF program */
static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
{
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7de98906ddf4a..b608185e1ffd5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4864,7 +4864,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
if (err)
return err;

- if (func_id == BPF_FUNC_get_stack && !env->prog->has_callchain_buf) {
+ if ((func_id == BPF_FUNC_get_stack ||
+ func_id == BPF_FUNC_get_task_stack) &&
+ !env->prog->has_callchain_buf) {
const char *err_str;

#ifdef CONFIG_PERF_EVENTS
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 5d59dda5f6615..977ba3b6f6c64 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1137,6 +1137,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_ringbuf_query_proto;
case BPF_FUNC_jiffies64:
return &bpf_jiffies64_proto;
+ case BPF_FUNC_get_task_stack:
+ return &bpf_get_task_stack_proto;
default:
return NULL;
}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 6bab40ff442e8..dd12e3b18aae3 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -426,6 +426,7 @@ class PrinterHelpers(Printer):
'struct tcp_timewait_sock',
'struct tcp_request_sock',
'struct udp6_sock',
+ 'struct task_struct',

'struct __sk_buff',
'struct sk_msg_md',
@@ -468,6 +469,7 @@ class PrinterHelpers(Printer):
'struct tcp_timewait_sock',
'struct tcp_request_sock',
'struct udp6_sock',
+ 'struct task_struct',
}
mapped_types = {
'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 0cb8ec9488168..54106ea667211 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3285,6 +3285,39 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
* Return
* *sk* if casting is valid, or NULL otherwise.
+ *
+ * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
+ * Description
+ * Return a user or a kernel stack in bpf program provided buffer.
+ * To achieve this, the helper needs *task*, which is a valid
+ * pointer to struct task_struct. To store the stacktrace, the
+ * bpf program provides *buf* with a nonnegative *size*.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_USER_BUILD_ID**
+ * Collect buildid+offset instead of ips for user stack,
+ * only valid if **BPF_F_USER_STACK** is also specified.
+ *
+ * **bpf_get_task_stack**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
+ * to sufficient large buffer size. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * A non-negative value equal to or less than *size* on success,
+ * or a negative error in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3427,7 +3460,8 @@ union bpf_attr {
FN(skc_to_tcp_sock), \
FN(skc_to_tcp_timewait_sock), \
FN(skc_to_tcp_request_sock), \
- FN(skc_to_udp6_sock),
+ FN(skc_to_udp6_sock), \
+ FN(get_task_stack),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
--
2.24.1