Commit fa28dcb8 authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov

bpf: Introduce helper bpf_get_task_stack()

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.
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200630062846.664389-3-songliubraving@fb.com
parent d141b8bc
......@@ -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;
......
......@@ -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 +3460,9 @@ 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
......
......@@ -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;
trace = get_perf_callchain(regs, init_nr, kernel, user,
sysctl_perf_event_max_stack, false, false);
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);
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)
{
......
......@@ -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
......
......@@ -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;
}
......
......@@ -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',
......
......@@ -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 +3460,9 @@ 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
......
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