Gianluca Borello 5722569bb9 bpf: allow helpers access to map element values ... Enable helpers to directly access a map element value by passing a register type PTR_TO_MAP_VALUE (or PTR_TO_MAP_VALUE_ADJ) to helper arguments ARG_PTR_TO_STACK or ARG_PTR_TO_RAW_STACK. This enables several use cases. For example, a typical tracing program might want to capture pathnames passed to sys_open() with: struct trace_data { char pathname[PATHLEN]; }; SEC("kprobe/sys_open") void bpf_sys_open(struct pt_regs *ctx) { struct trace_data data; bpf_probe_read(data.pathname, sizeof(data.pathname), ctx->di); /* consume data.pathname, for example via * bpf_trace_printk() or bpf_perf_event_output() */ } Such a program could easily hit the stack limit in case PATHLEN needs to be large or more local variables need to exist, both of which are quite common scenarios. Allowing direct helper access to map element values, one could do: struct bpf_map_def SEC("maps") scratch_map = { .type = BPF_MAP_TYPE_PERCPU_ARRAY, .key_size = sizeof(u32), .value_size = sizeof(struct trace_data), .max_entries = 1, }; SEC("kprobe/sys_open") int bpf_sys_open(struct pt_regs *ctx) { int id = 0; struct trace_data *p = bpf_map_lookup_elem(&scratch_map, &id); if (!p) return; bpf_probe_read(p->pathname, sizeof(p->pathname), ctx->di); /* consume p->pathname, for example via * bpf_trace_printk() or bpf_perf_event_output() */ } And wouldn't risk exhausting the stack. Code changes are loosely modeled after commit 6841de8b0d ("bpf: allow helpers access the packet directly"). Unlike with PTR_TO_PACKET, these changes just work with ARG_PTR_TO_STACK and ARG_PTR_TO_RAW_STACK (not ARG_PTR_TO_MAP_KEY, ARG_PTR_TO_MAP_VALUE, ...): adding those would be trivial, but since there is not currently a use case for that, it's reasonable to limit the set of changes. Also, add new tests to make sure accesses to map element values from helpers never go out of boundary, even when adjusted. Signed-off-by: Gianluca Borello <g.borello@gmail.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>		2017-01-09 16:56:26 -05:00
..
arraymap.c	bpf: Add bpf_current_task_under_cgroup helper	2016-08-12 21:49:41 -07:00
bpf_lru_list.c	bpf: Fix compilation warning in __bpf_lru_list_rotate_inactive	2016-11-16 11:30:56 -05:00
bpf_lru_list.h	bpf: Add percpu LRU list	2016-11-15 11:50:20 -05:00
cgroup.c	bpf: Add new cgroup attach type to enable sock modifications	2016-12-02 13:46:08 -05:00
core.c	bpf: fix overflow in prog accounting	2016-12-17 21:27:44 -05:00
hashtab.c	bpf: Add BPF_MAP_TYPE_LRU_PERCPU_HASH	2016-11-15 11:50:20 -05:00
helpers.c	bpf: add helper for retrieving current numa node id	2016-10-22 17:05:52 -04:00
inode.c	bpf: allow for mount options to specify permissions	2016-11-27 20:38:47 -05:00
Makefile	cgroup: add support for eBPF programs	2016-11-25 16:25:52 -05:00
percpu_freelist.c	bpf: introduce percpu_freelist	2016-03-08 15:28:31 -05:00
percpu_freelist.h	bpf: introduce percpu_freelist	2016-03-08 15:28:31 -05:00
stackmap.c	bpf: add BPF_CALL_x macros for declaring helpers	2016-09-09 19:36:04 -07:00
syscall.c	bpf: fix overflow in prog accounting	2016-12-17 21:27:44 -05:00
verifier.c	bpf: allow helpers access to map element values	2017-01-09 16:56:26 -05:00