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authorDaniel Borkmann <daniel@iogearbox.net>2017-12-20 13:42:57 +0100
committerAlexei Starovoitov <ast@kernel.org>2017-12-21 03:09:40 +0100
commit7105e828c087de970fcb5a9509db51bfe6bd7894 (patch)
tree47cca432779b910dab12ee5cc81b792f6e432a76 /kernel/bpf/core.c
parentbpf: fix kallsyms handling for subprogs (diff)
downloadlinux-7105e828c087de970fcb5a9509db51bfe6bd7894.tar.xz
linux-7105e828c087de970fcb5a9509db51bfe6bd7894.zip
bpf: allow for correlation of maps and helpers in dump
Currently a dump of an xlated prog (post verifier stage) doesn't correlate used helpers as well as maps. The prog info lists involved map ids, however there's no correlation of where in the program they are used as of today. Likewise, bpftool does not correlate helper calls with the target functions. The latter can be done w/o any kernel changes through kallsyms, and also has the advantage that this works with inlined helpers and BPF calls. Example, via interpreter: # tc filter show dev foo ingress filter protocol all pref 49152 bpf chain 0 filter protocol all pref 49152 bpf chain 0 handle 0x1 foo.o:[ingress] \ direct-action not_in_hw id 1 tag c74773051b364165 <-- prog id:1 * Output before patch (calls/maps remain unclear): # bpftool prog dump xlated id 1 <-- dump prog id:1 0: (b7) r1 = 2 1: (63) *(u32 *)(r10 -4) = r1 2: (bf) r2 = r10 3: (07) r2 += -4 4: (18) r1 = 0xffff95c47a8d4800 6: (85) call unknown#73040 7: (15) if r0 == 0x0 goto pc+18 8: (bf) r2 = r10 9: (07) r2 += -4 10: (bf) r1 = r0 11: (85) call unknown#73040 12: (15) if r0 == 0x0 goto pc+23 [...] * Output after patch: # bpftool prog dump xlated id 1 0: (b7) r1 = 2 1: (63) *(u32 *)(r10 -4) = r1 2: (bf) r2 = r10 3: (07) r2 += -4 4: (18) r1 = map[id:2] <-- map id:2 6: (85) call bpf_map_lookup_elem#73424 <-- helper call 7: (15) if r0 == 0x0 goto pc+18 8: (bf) r2 = r10 9: (07) r2 += -4 10: (bf) r1 = r0 11: (85) call bpf_map_lookup_elem#73424 12: (15) if r0 == 0x0 goto pc+23 [...] # bpftool map show id 2 <-- show/dump/etc map id:2 2: hash_of_maps flags 0x0 key 4B value 4B max_entries 3 memlock 4096B Example, JITed, same prog: # tc filter show dev foo ingress filter protocol all pref 49152 bpf chain 0 filter protocol all pref 49152 bpf chain 0 handle 0x1 foo.o:[ingress] \ direct-action not_in_hw id 3 tag c74773051b364165 jited # bpftool prog show id 3 3: sched_cls tag c74773051b364165 loaded_at Dec 19/13:48 uid 0 xlated 384B jited 257B memlock 4096B map_ids 2 # bpftool prog dump xlated id 3 0: (b7) r1 = 2 1: (63) *(u32 *)(r10 -4) = r1 2: (bf) r2 = r10 3: (07) r2 += -4 4: (18) r1 = map[id:2] <-- map id:2 6: (85) call __htab_map_lookup_elem#77408 <-+ inlined rewrite 7: (15) if r0 == 0x0 goto pc+2 | 8: (07) r0 += 56 | 9: (79) r0 = *(u64 *)(r0 +0) <-+ 10: (15) if r0 == 0x0 goto pc+24 11: (bf) r2 = r10 12: (07) r2 += -4 [...] Example, same prog, but kallsyms disabled (in that case we are also not allowed to pass any relative offsets, etc, so prog becomes pointer sanitized on dump): # sysctl kernel.kptr_restrict=2 kernel.kptr_restrict = 2 # bpftool prog dump xlated id 3 0: (b7) r1 = 2 1: (63) *(u32 *)(r10 -4) = r1 2: (bf) r2 = r10 3: (07) r2 += -4 4: (18) r1 = map[id:2] 6: (85) call bpf_unspec#0 7: (15) if r0 == 0x0 goto pc+2 [...] Example, BPF calls via interpreter: # bpftool prog dump xlated id 1 0: (85) call pc+2#__bpf_prog_run_args32 1: (b7) r0 = 1 2: (95) exit 3: (b7) r0 = 2 4: (95) exit Example, BPF calls via JIT: # sysctl net.core.bpf_jit_enable=1 net.core.bpf_jit_enable = 1 # sysctl net.core.bpf_jit_kallsyms=1 net.core.bpf_jit_kallsyms = 1 # bpftool prog dump xlated id 1 0: (85) call pc+2#bpf_prog_3b185187f1855c4c_F 1: (b7) r0 = 1 2: (95) exit 3: (b7) r0 = 2 4: (95) exit And finally, an example for tail calls that is now working as well wrt correlation: # bpftool prog dump xlated id 2 [...] 10: (b7) r2 = 8 11: (85) call bpf_trace_printk#-41312 12: (bf) r1 = r6 13: (18) r2 = map[id:1] 15: (b7) r3 = 0 16: (85) call bpf_tail_call#12 17: (b7) r1 = 42 18: (6b) *(u16 *)(r6 +46) = r1 19: (b7) r0 = 0 20: (95) exit # bpftool map show id 1 1: prog_array flags 0x0 key 4B value 4B max_entries 1 memlock 4096B Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/core.c')
-rw-r--r--kernel/bpf/core.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 768e0a02d8c8..70a534549cd3 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -771,7 +771,9 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
/* Base function for offset calculation. Needs to go into .text section,
* therefore keeping it non-static as well; will also be used by JITs
- * anyway later on, so do not let the compiler omit it.
+ * anyway later on, so do not let the compiler omit it. This also needs
+ * to go into kallsyms for correlation from e.g. bpftool, so naming
+ * must not change.
*/
noinline u64 __bpf_call_base(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
{