bpf: Add BPF_F_ANY_ALIGNMENT.

Often we want to write tests cases that check things like bad context offset accesses. And one way to do this is to use an odd offset on, for example, a 32-bit load. This unfortunately triggers the alignment checks first on platforms that do not set CONFIG_EFFICIENT_UNALIGNED_ACCESS. So the test case see the alignment failure rather than what it was testing for. It is often not completely possible to respect the original intention of the test, or even test the same exact thing, while solving the alignment issue. Another option could have been to check the alignment after the context and other validations are performed by the verifier, but that is a non-trivial change to the verifier.

David Miller committed 7 years ago

Commit e9ee9ef1 parent 88945f48 files · +45 −9Browse files

Unified · Split

8 files

include/uapi/linux/bpf.h +14 −0
kernel/bpf/syscall.c +6 −1
kernel/bpf/verifier.c +2 −0
tools/include/uapi/linux/bpf.h +14 −0
tools/lib/bpf/bpf.c +4 −4
tools/lib/bpf/bpf.h +1 −1
tools/testing/selftests/bpf/test_align.c +2 −2
tools/testing/selftests/bpf/test_verifier.c +2 −1

include/uapi/linux/bpf.h+14−0

@@ -232,6 +232,20 @@ enum bpf_attach_type { · 231 unmodified lines
232	232	*/
233	233	#define BPF_F_STRICT_ALIGNMENT (1U << 0)
234	234
	235	+/* If BPF_F_ANY_ALIGNMENT is used in BPF_PROF_LOAD command, the
	236	+ * verifier will allow any alignment whatsoever. On platforms
	237	+ * with strict alignment requirements for loads ands stores (such
	238	+ * as sparc and mips) the verifier validates that all loads and
	239	+ * stores provably follow this requirement. This flag turns that
	240	+ * checking and enforcement off.
	241	+ *
	242	+ * It is mostly used for testing when we want to validate the
	243	+ * context and memory access aspects of the verifier, but because
	244	+ * of an unaligned access the alignment check would trigger before
	245	+ * the one we are interested in.
	246	+ */
	247	+#define BPF_F_ANY_ALIGNMENT (1U << 1)
	248	+
235	249	/* when bpf_ldimm64->src_reg == BPF_PSEUDO_MAP_FD, bpf_ldimm64->imm == fd */
236	250	#define BPF_PSEUDO_MAP_FD 1
237	251

kernel/bpf/syscall.c+6−1

@@ -1452,9 +1452,14 @@ static int bpf_prog_load(union bpf_attr attr, union bpf_attr __user uattr) · 1451 unmodified lines
1452	1452	if (CHECK_ATTR(BPF_PROG_LOAD))
1453	1453	return -EINVAL;
1454	1454
1455		− if (attr->prog_flags & ~BPF_F_STRICT_ALIGNMENT)
	1455	+ if (attr->prog_flags & ~(BPF_F_STRICT_ALIGNMENT \| BPF_F_ANY_ALIGNMENT))
1456	1456	return -EINVAL;
1457	1457
	1458	+ if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
	1459	+ (attr->prog_flags & BPF_F_ANY_ALIGNMENT) &&
	1460	+ !capable(CAP_SYS_ADMIN))
	1461	+ return -EPERM;
	1462	+
1458	1463	/* copy eBPF program license from user space */
1459	1464	if (strncpy_from_user(license, u64_to_user_ptr(attr->license),
1460	1465	sizeof(license) - 1) < 0)

kernel/bpf/verifier.c+2−0

@@ -6505,6 +6505,8 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr attr, · 6504 unmodified lines
6505	6505	env->strict_alignment = !!(attr->prog_flags & BPF_F_STRICT_ALIGNMENT);
6506	6506	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
6507	6507	env->strict_alignment = true;
	6508	+ if (attr->prog_flags & BPF_F_ANY_ALIGNMENT)
	6509	+ env->strict_alignment = false;
6508	6510
6509	6511	ret = replace_map_fd_with_map_ptr(env);
6510	6512	if (ret < 0)

tools/include/uapi/linux/bpf.h+14−0

@@ -232,6 +232,20 @@ enum bpf_attach_type { · 231 unmodified lines
232	232	*/
233	233	#define BPF_F_STRICT_ALIGNMENT (1U << 0)
234	234
	235	+/* If BPF_F_ANY_ALIGNMENT is used in BPF_PROF_LOAD command, the
	236	+ * verifier will allow any alignment whatsoever. On platforms
	237	+ * with strict alignment requirements for loads ands stores (such
	238	+ * as sparc and mips) the verifier validates that all loads and
	239	+ * stores provably follow this requirement. This flag turns that
	240	+ * checking and enforcement off.
	241	+ *
	242	+ * It is mostly used for testing when we want to validate the
	243	+ * context and memory access aspects of the verifier, but because
	244	+ * of an unaligned access the alignment check would trigger before
	245	+ * the one we are interested in.
	246	+ */
	247	+#define BPF_F_ANY_ALIGNMENT (1U << 1)
	248	+
235	249	/* when bpf_ldimm64->src_reg == BPF_PSEUDO_MAP_FD, bpf_ldimm64->imm == fd */
236	250	#define BPF_PSEUDO_MAP_FD 1
237	251

tools/lib/bpf/bpf.c+4−4

@@ -279,9 +279,9 @@ int bpf_load_program(enum bpf_prog_type type, const struct bpf_insn *insns, · 278 unmodified lines
279	279	}
280	280
281	281	int bpf_verify_program(enum bpf_prog_type type, const struct bpf_insn *insns,
282		− size_t insns_cnt, int strict_alignment,
283		− const char *license, __u32 kern_version,
284		− char *log_buf, size_t log_buf_sz, int log_level)
	282	+ size_t insns_cnt, __u32 prog_flags, const char *license,
	283	+ __u32 kern_version, char *log_buf, size_t log_buf_sz,
	284	+ int log_level)
285	285	{
286	286	union bpf_attr attr;
287	287
@@ -295,7 +295,7 @@ int bpf_verify_program(enum bpf_prog_type type, const struct bpf_insn *insns, · 7 unmodified lines
295	295	attr.log_level = log_level;
296	296	log_buf[0] = 0;
297	297	attr.kern_version = kern_version;
298		− attr.prog_flags = strict_alignment ? BPF_F_STRICT_ALIGNMENT : 0;
	298	+ attr.prog_flags = prog_flags;
299	299
300	300	return sys_bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
301	301	}

tools/lib/bpf/bpf.h+1−1

@@ -98,7 +98,7 @@ LIBBPF_API int bpf_load_program(enum bpf_prog_type type, · 97 unmodified lines
98	98	char *log_buf, size_t log_buf_sz);
99	99	LIBBPF_API int bpf_verify_program(enum bpf_prog_type type,
100	100	const struct bpf_insn *insns,
101		− size_t insns_cnt, int strict_alignment,
	101	+ size_t insns_cnt, __u32 prog_flags,
102	102	const char *license, __u32 kern_version,
103	103	char *log_buf, size_t log_buf_sz,
104	104	int log_level);

tools/testing/selftests/bpf/test_align.c+2−2

@@ -620,8 +620,8 @@ static int do_test_single(struct bpf_align_test *test) · 619 unmodified lines
620	620
621	621	prog_len = probe_filter_length(prog);
622	622	fd_prog = bpf_verify_program(prog_type ? : BPF_PROG_TYPE_SOCKET_FILTER,
623		− prog, prog_len, 1, "GPL", 0,
624		− bpf_vlog, sizeof(bpf_vlog), 2);
	623	+ prog, prog_len, BPF_F_STRICT_ALIGNMENT,
	624	+ "GPL", 0, bpf_vlog, sizeof(bpf_vlog), 2);
625	625	if (fd_prog < 0 && test->result != REJECT) {
626	626	printf("Failed to load program.\n");
627	627	printf("%s", bpf_vlog);

tools/testing/selftests/bpf/test_verifier.c+2−1

@@ -14275,7 +14275,8 @@ static void do_test_single(struct bpf_test *test, bool unpriv, · 14274 unmodified lines
14275	14275	prog_len = probe_filter_length(prog);
14276	14276
14277	14277	fd_prog = bpf_verify_program(prog_type, prog, prog_len,
14278		− test->flags & F_LOAD_WITH_STRICT_ALIGNMENT,
	14278	+ test->flags & F_LOAD_WITH_STRICT_ALIGNMENT ?
	14279	+ BPF_F_STRICT_ALIGNMENT : 0,
14279	14280	"GPL", 0, bpf_vlog, sizeof(bpf_vlog), 1);
14280	14281
14281	14282	expected_ret = unpriv && test->result_unpriv != UNDEF ?