bpf: permits narrower load from bpf program context fields

Currently, verifier will reject a program if it contains an
narrower load from the bpf context structure. For example,
        __u8 h = __sk_buff->hash, or
        __u16 p = __sk_buff->protocol
        __u32 sample_period = bpf_perf_event_data->sample_period
which are narrower loads of 4-byte or 8-byte field.

This patch solves the issue by:
  . Introduce a new parameter ctx_field_size to carry the
    field size of narrower load from prog type
    specific *__is_valid_access validator back to verifier.
  . The non-zero ctx_field_size for a memory access indicates
    (1). underlying prog type specific convert_ctx_accesses
         supporting non-whole-field access
    (2). the current insn is a narrower or whole field access.
  . In verifier, for such loads where load memory size is
    less than ctx_field_size, verifier transforms it
    to a full field load followed by proper masking.
  . Currently, __sk_buff and bpf_perf_event_data->sample_period
    are supporting narrowing loads.
  . Narrower stores are still not allowed as typical ctx stores
    are just normal stores.

Because of this change, some tests in verifier will fail and
these tests are removed. As a bonus, rename some out of bound
__sk_buff->cb access to proper field name and remove two
redundant "skb cb oob" tests.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 79 deletions

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 4ee4708b0d60..13341700930c 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -1073,44 +1073,22 @@ static struct bpf_test tests[] = {
 		.result = ACCEPT,
 	},
 	{
-		"check cb access: byte, oob 1",
+		"__sk_buff->hash, offset 0, byte store not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[4]) + 4),
+				    offsetof(struct __sk_buff, hash)),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",
 		.result = REJECT,
 	},
 	{
-		"check cb access: byte, oob 2",
+		"__sk_buff->tc_index, offset 3, byte store not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[0]) - 1),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: byte, oob 3",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[4]) + 4),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: byte, oob 4",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[0]) - 1),
+				    offsetof(struct __sk_buff, tc_index) + 3),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",
@@ -1188,44 +1166,22 @@ static struct bpf_test tests[] = {
 		.result = REJECT,
 	},
 	{
-		"check cb access: half, oob 1",
+		"check __sk_buff->hash, offset 0, half store not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[4]) + 4),
+				    offsetof(struct __sk_buff, hash)),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",
 		.result = REJECT,
 	},
 	{
-		"check cb access: half, oob 2",
+		"check __sk_buff->tc_index, offset 2, half store not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[0]) - 2),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: half, oob 3",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[4]) + 4),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: half, oob 4",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[0]) - 2),
+				    offsetof(struct __sk_buff, tc_index) + 2),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",
@@ -1368,28 +1324,6 @@ static struct bpf_test tests[] = {
 		"check cb access: double, oob 2",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[4]) + 8),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: double, oob 3",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
-				    offsetof(struct __sk_buff, cb[0]) - 8),
-			BPF_EXIT_INSN(),
-		},
-		.errstr = "invalid bpf_context access",
-		.result = REJECT,
-	},
-	{
-		"check cb access: double, oob 4",
-		.insns = {
-			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
 				    offsetof(struct __sk_buff, cb[4])),
 			BPF_EXIT_INSN(),
@@ -1398,22 +1332,22 @@ static struct bpf_test tests[] = {
 		.result = REJECT,
 	},
 	{
-		"check cb access: double, oob 5",
+		"check __sk_buff->ifindex dw store not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[4]) + 8),
+			BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct __sk_buff, ifindex)),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",
 		.result = REJECT,
 	},
 	{
-		"check cb access: double, oob 6",
+		"check __sk_buff->ifindex dw load not permitted",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
 			BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
-				    offsetof(struct __sk_buff, cb[0]) - 8),
+				    offsetof(struct __sk_buff, ifindex)),
 			BPF_EXIT_INSN(),
 		},
 		.errstr = "invalid bpf_context access",