Commit 7b04d6d6 authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

bpf: Separate bpf_get_[stack|stackid] for perf events BPF 



Calling get_perf_callchain() on perf_events from PEBS entries may cause
unwinder errors. To fix this issue, the callchain is fetched early. Such
perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY.

Similarly, calling bpf_get_[stack|stackid] on perf_events from PEBS may
also cause unwinder errors. To fix this, add separate version of these
two helpers, bpf_get_[stack|stackid]_pe. These two hepers use callchain in
bpf_perf_event_data_kern->data->callchain.

Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723180648.1429892-2-songliubraving@fb.com
parent 909e446b

include/linux/bpf.h

+2 −0
Original line number Diff line number Diff line
@@ -1675,6 +1675,8 @@ 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_get_stackid_proto_pe;

extern const struct bpf_func_proto bpf_get_stack_proto_pe;

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;

kernel/bpf/stackmap.c

+166 −18
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
#include <linux/bpf.h>

#include <linux/jhash.h>

#include <linux/filter.h>

#include <linux/kernel.h>

#include <linux/stacktrace.h>

#include <linux/perf_event.h>

#include <linux/elf.h>
@@ -387,11 +388,10 @@ get_callchain_entry_for_task(struct task_struct *task, u32 init_nr) 
#endif

}



BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,

	   u64, flags)

static long __bpf_get_stackid(struct bpf_map *map,

			      struct perf_callchain_entry *trace, u64 flags)

{

	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);

	struct perf_callchain_entry *trace;

	struct stack_map_bucket *bucket, *new_bucket, *old_bucket;

	u32 max_depth = map->value_size / stack_map_data_size(map);

	/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
@@ -399,21 +399,9 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, 
	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;

	u32 hash, id, trace_nr, trace_len;

	bool user = flags & BPF_F_USER_STACK;

	bool kernel = !user;

	u64 *ips;

	bool hash_matches;



	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |

			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))

		return -EINVAL;



	trace = get_perf_callchain(regs, init_nr, kernel, user,

				   sysctl_perf_event_max_stack, false, false);



	if (unlikely(!trace))

		/* couldn't fetch the stack trace */

		return -EFAULT;



	/* get_perf_callchain() guarantees that trace->nr >= init_nr

	 * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth

	 */
@@ -478,6 +466,30 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, 
	return id;

}



BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,

	   u64, flags)

{

	u32 max_depth = map->value_size / stack_map_data_size(map);

	/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */

	u32 init_nr = sysctl_perf_event_max_stack - max_depth;

	bool user = flags & BPF_F_USER_STACK;

	struct perf_callchain_entry *trace;

	bool kernel = !user;



	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |

			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))

		return -EINVAL;



	trace = get_perf_callchain(regs, init_nr, kernel, user,

				   sysctl_perf_event_max_stack, false, false);



	if (unlikely(!trace))

		/* couldn't fetch the stack trace */

		return -EFAULT;



	return __bpf_get_stackid(map, trace, flags);

}



const struct bpf_func_proto bpf_get_stackid_proto = {

	.func		= bpf_get_stackid,

	.gpl_only	= true,
@@ -487,7 +499,77 @@ const struct bpf_func_proto bpf_get_stackid_proto = { 
	.arg3_type	= ARG_ANYTHING,

};



static __u64 count_kernel_ip(struct perf_callchain_entry *trace)

{

	__u64 nr_kernel = 0;



	while (nr_kernel < trace->nr) {

		if (trace->ip[nr_kernel] == PERF_CONTEXT_USER)

			break;

		nr_kernel++;

	}

	return nr_kernel;

}



BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,

	   struct bpf_map *, map, u64, flags)

{

	struct perf_event *event = ctx->event;

	struct perf_callchain_entry *trace;

	bool kernel, user;

	__u64 nr_kernel;

	int ret;



	/* perf_sample_data doesn't have callchain, use bpf_get_stackid */

	if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))

		return bpf_get_stackid((unsigned long)(ctx->regs),

				       (unsigned long) map, flags, 0, 0);



	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |

			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))

		return -EINVAL;



	user = flags & BPF_F_USER_STACK;

	kernel = !user;



	trace = ctx->data->callchain;

	if (unlikely(!trace))

		return -EFAULT;



	nr_kernel = count_kernel_ip(trace);



	if (kernel) {

		__u64 nr = trace->nr;



		trace->nr = nr_kernel;

		ret = __bpf_get_stackid(map, trace, flags);



		/* restore nr */

		trace->nr = nr;

	} else { /* user */

		u64 skip = flags & BPF_F_SKIP_FIELD_MASK;



		skip += nr_kernel;

		if (skip > BPF_F_SKIP_FIELD_MASK)

			return -EFAULT;



		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;

		ret = __bpf_get_stackid(map, trace, flags);

	}

	return ret;

}



const struct bpf_func_proto bpf_get_stackid_proto_pe = {

	.func		= bpf_get_stackid_pe,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_CONST_MAP_PTR,

	.arg3_type	= ARG_ANYTHING,

};



static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,

			    struct perf_callchain_entry *trace_in,

			    void *buf, u32 size, u64 flags)

{

	u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
@@ -520,7 +602,9 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, 
	else

		init_nr = sysctl_perf_event_max_stack - num_elem;



	if (kernel && task)

	if (trace_in)

		trace = trace_in;

	else if (kernel && task)

		trace = get_callchain_entry_for_task(task, init_nr);

	else

		trace = get_perf_callchain(regs, init_nr, kernel, user,
@@ -556,7 +640,7 @@ clear: 
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);

	return __bpf_get_stack(regs, NULL, NULL, buf, size, flags);

}



const struct bpf_func_proto bpf_get_stack_proto = {
@@ -574,7 +658,7 @@ BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf, 
{

	struct pt_regs *regs = task_pt_regs(task);



	return __bpf_get_stack(regs, task, buf, size, flags);

	return __bpf_get_stack(regs, task, NULL, buf, size, flags);

}



BTF_ID_LIST(bpf_get_task_stack_btf_ids)
@@ -591,6 +675,70 @@ const struct bpf_func_proto bpf_get_task_stack_proto = { 
	.btf_id		= bpf_get_task_stack_btf_ids,

};



BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,

	   void *, buf, u32, size, u64, flags)

{

	struct perf_event *event = ctx->event;

	struct perf_callchain_entry *trace;

	bool kernel, user;

	int err = -EINVAL;

	__u64 nr_kernel;



	if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))

		return __bpf_get_stack(ctx->regs, NULL, NULL, buf, size, flags);



	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |

			       BPF_F_USER_BUILD_ID)))

		goto clear;



	user = flags & BPF_F_USER_STACK;

	kernel = !user;



	err = -EFAULT;

	trace = ctx->data->callchain;

	if (unlikely(!trace))

		goto clear;



	nr_kernel = count_kernel_ip(trace);



	if (kernel) {

		__u64 nr = trace->nr;



		trace->nr = nr_kernel;

		err = __bpf_get_stack(ctx->regs, NULL, trace, buf,

				      size, flags);



		/* restore nr */

		trace->nr = nr;

	} else { /* user */

		u64 skip = flags & BPF_F_SKIP_FIELD_MASK;



		skip += nr_kernel;

		if (skip > BPF_F_SKIP_FIELD_MASK)

			goto clear;



		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;

		err = __bpf_get_stack(ctx->regs, NULL, trace, buf,

				      size, flags);

	}

	return err;



clear:

	memset(buf, 0, size);

	return err;



}



const struct bpf_func_proto bpf_get_stack_proto_pe = {

	.func		= bpf_get_stack_pe,

	.gpl_only	= true,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_PTR_TO_UNINIT_MEM,

	.arg3_type	= ARG_CONST_SIZE_OR_ZERO,

	.arg4_type	= ARG_ANYTHING,

};



/* Called from eBPF program */

static void *stack_map_lookup_elem(struct bpf_map *map, void *key)

{

kernel/trace/bpf_trace.c

+2 −2
Original line number Diff line number Diff line
@@ -1411,9 +1411,9 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
	case BPF_FUNC_perf_event_output:

		return &bpf_perf_event_output_proto_tp;

	case BPF_FUNC_get_stackid:

		return &bpf_get_stackid_proto_tp;

		return &bpf_get_stackid_proto_pe;

	case BPF_FUNC_get_stack:

		return &bpf_get_stack_proto_tp;

		return &bpf_get_stack_proto_pe;

	case BPF_FUNC_perf_prog_read_value:

		return &bpf_perf_prog_read_value_proto;

	case BPF_FUNC_read_branch_records:

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