bpf: Add support for BTF pointers to interpreter

Pointer to BTF object is a pointer to kernel object or NULL. The memory access in the interpreter has to be done via probe_kernel_read to avoid page faults.

Alexei Starovoitov committed 7 years ago

Commit 2a027591 parent ac4414b3 files · +30 −0Browse files

Unified · Split

3 files

include/linux/filter.h +3 −0
kernel/bpf/core.c +19 −0
kernel/bpf/verifier.c +8 −0

include/linux/filter.h+3−0

@@ -65,6 +65,9 @@ struct ctl_table_header; · 64 unmodified lines
65	65	/* unused opcode to mark special call to bpf_tail_call() helper */
66	66	#define BPF_TAIL_CALL 0xf0
67	67
	68	+/* unused opcode to mark special load instruction. Same as BPF_ABS */
	69	+#define BPF_PROBE_MEM 0x20
	70	+
68	71	/* unused opcode to mark call to interpreter with arguments */
69	72	#define BPF_CALL_ARGS 0xe0
70	73

kernel/bpf/core.c+19−0

@@ -1291,6 +1291,11 @@ bool bpf_opcode_in_insntable(u8 code) · 1290 unmodified lines
1291	1291	}
1292	1292
1293	1293	#ifndef CONFIG_BPF_JIT_ALWAYS_ON
	1294	+u64 __weak bpf_probe_read(void * dst, u32 size, const void * unsafe_ptr)
	1295	+{
	1296	+ memset(dst, 0, size);
	1297	+ return -EFAULT;
	1298	+}
1294	1299	/**
1295	1300	* __bpf_prog_run - run eBPF program on a given context
1296	1301	* @regs: is the array of MAX_BPF_EXT_REG eBPF pseudo-registers
@@ -1310,6 +1315,10 @@ static u64 __no_fgcse ___bpf_prog_run(u64 regs, const struct bpf_insn insn, u6 · 13 unmodified lines
1310	1315	/* Non-UAPI available opcodes. */
1311	1316	[BPF_JMP \| BPF_CALL_ARGS] = &&JMP_CALL_ARGS,
1312	1317	[BPF_JMP \| BPF_TAIL_CALL] = &&JMP_TAIL_CALL,
	1318	+ [BPF_LDX \| BPF_PROBE_MEM \| BPF_B] = &&LDX_PROBE_MEM_B,
	1319	+ [BPF_LDX \| BPF_PROBE_MEM \| BPF_H] = &&LDX_PROBE_MEM_H,
	1320	+ [BPF_LDX \| BPF_PROBE_MEM \| BPF_W] = &&LDX_PROBE_MEM_W,
	1321	+ [BPF_LDX \| BPF_PROBE_MEM \| BPF_DW] = &&LDX_PROBE_MEM_DW,
1313	1322	};
1314	1323	#undef BPF_INSN_3_LBL
1315	1324	#undef BPF_INSN_2_LBL
@@ -1542,6 +1551,16 @@ out: · 226 unmodified lines
1542	1551	LDST(W, u32)
1543	1552	LDST(DW, u64)
1544	1553	#undef LDST
	1554	+#define LDX_PROBE(SIZEOP, SIZE) \
	1555	+ LDX_PROBE_MEM_##SIZEOP: \
	1556	+ bpf_probe_read(&DST, SIZE, (const void *)(long) SRC); \
	1557	+ CONT;
	1558	+ LDX_PROBE(B, 1)
	1559	+ LDX_PROBE(H, 2)
	1560	+ LDX_PROBE(W, 4)
	1561	+ LDX_PROBE(DW, 8)
	1562	+#undef LDX_PROBE
	1563	+
1545	1564	STX_XADD_W: /* lock xadd (u32 )(dst_reg + off16) += src_reg */
1546	1565	atomic_add((u32) SRC, (atomic_t *)(unsigned long)
1547	1566	(DST + insn->off));

kernel/bpf/verifier.c+8−0

@@ -7581,6 +7581,7 @@ static bool reg_type_mismatch_ok(enum bpf_reg_type type) · 7580 unmodified lines
7581	7581	case PTR_TO_TCP_SOCK:
7582	7582	case PTR_TO_TCP_SOCK_OR_NULL:
7583	7583	case PTR_TO_XDP_SOCK:
	7584	+ case PTR_TO_BTF_ID:
7584	7585	return false;
7585	7586	default:
7586	7587	return true;
@@ -8722,6 +8723,13 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) · 1135 unmodified lines
8722	8723	case PTR_TO_XDP_SOCK:
8723	8724	convert_ctx_access = bpf_xdp_sock_convert_ctx_access;
8724	8725	break;
	8726	+ case PTR_TO_BTF_ID:
	8727	+ if (type == BPF_WRITE) {
	8728	+ verbose(env, "Writes through BTF pointers are not allowed\n");
	8729	+ return -EINVAL;
	8730	+ }
	8731	+ insn->code = BPF_LDX \| BPF_PROBE_MEM \| BPF_SIZE((insn)->code);
	8732	+ continue;
8725	8733	default:
8726	8734	continue;
8727	8735	}

bpf: Add support for BTF pointers to interpreter

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