[iovisor-dev] [PATCH RFC v2] bpf: allow map helpers access to map values directly

Alexei Starovoitov alexei.starovoitov at gmail.com
Tue Sep 12 01:14:59 UTC 2017


On Sat, Sep 09, 2017 at 04:31:16PM +0200, Paul Chaignon wrote:
> Helpers that expect ARG_PTR_TO_MAP_KEY and ARG_PTR_TO_MAP_VALUE can only
> access stack and packet memory.  Allow these helpers to directly access map
> values by passing registers of type PTR_TO_MAP_VALUE.
> 
> This change removes the need for an extra copy to the stack when using a
> map value to perform a second map lookup, as in the following:
> 
> struct bpf_map_def SEC("maps") infobyreq = {
>     .type = BPF_MAP_TYPE_HASHMAP,
>     .key_size = sizeof(struct request *),
>     .value_size = sizeof(struct info_t),
>     .max_entries = 1024,
> };
> struct bpf_map_def SEC("maps") counts = {
>     .type = BPF_MAP_TYPE_HASHMAP,
>     .key_size = sizeof(struct info_t),
>     .value_size = sizeof(u64),
>     .max_entries = 1024,
> };
> SEC("kprobe/blk_account_io_start")
> int bpf_blk_account_io_start(struct pt_regs *ctx)
> {
>     struct info_t *info = bpf_map_lookup_elem(&infobyreq, &ctx->di);
>     u64 *count = bpf_map_lookup_elem(&counts, info);
>     (*count)++;
> }
> 
> Signed-off-by: Paul Chaignon <paul.chaignon at orange.com>
> ---
> Changes in v2:
>   - Additional test cases for adjusted maps.
> 
>  kernel/bpf/verifier.c                       |  9 +++-
>  tools/testing/selftests/bpf/test_verifier.c | 84 +++++++++++++++++++++++++++++
>  2 files changed, 92 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index d690c7d..50e057d 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1351,7 +1351,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  	if (arg_type == ARG_PTR_TO_MAP_KEY ||
>  	    arg_type == ARG_PTR_TO_MAP_VALUE) {
>  		expected_type = PTR_TO_STACK;
> -		if (type != PTR_TO_PACKET && type != expected_type)
> +		if (type != PTR_TO_PACKET && type != PTR_TO_MAP_VALUE &&
> +		    type != expected_type)
>  			goto err_type;
>  	} else if (arg_type == ARG_CONST_SIZE ||
>  		   arg_type == ARG_CONST_SIZE_OR_ZERO) {
> @@ -1404,6 +1405,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  		if (type == PTR_TO_PACKET)
>  			err = check_packet_access(env, regno, reg->off,
>  						  meta->map_ptr->key_size);
> +		else if (type == PTR_TO_MAP_VALUE)
> +			err = check_map_access(env, regno, 0,
> +					       meta->map_ptr->key_size);
>  		else
>  			err = check_stack_boundary(env, regno,
>  						   meta->map_ptr->key_size,
> @@ -1420,6 +1424,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  		if (type == PTR_TO_PACKET)
>  			err = check_packet_access(env, regno, reg->off,
>  						  meta->map_ptr->value_size);
> +		else if (type == PTR_TO_MAP_VALUE)
> +			err = check_map_access(env, regno, 0,
> +					       meta->map_ptr->key_size);

as pointed out earlier. above is a bug.
please add negative test cases to see it.
See below...

>  		else
>  			err = check_stack_boundary(env, regno,
>  						   meta->map_ptr->value_size,
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index 8eb0995..4532066 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -5052,6 +5052,90 @@ static struct bpf_test tests[] = {
>  		.prog_type = BPF_PROG_TYPE_TRACEPOINT,
>  	},
>  	{
> +		"map helper access to map",
> +		.insns = {
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +			BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 4),
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_EXIT_INSN(),
> +		},
> +		.fixup_map1 = { 3, 8 },
> +		.result = ACCEPT,
> +		.prog_type = BPF_PROG_TYPE_TRACEPOINT,
> +	},
> +	{
> +		"map helper access to adjusted map (via const imm)",
> +		.insns = {
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +			BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 5),
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
> +			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2,
> +				      offsetof(struct test_val, foo)),

there are few bugs here.
1. it adds 4 byte, so it should have been rejected as misaligned.
2. if you add 100 here, it will still pass.

> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_EXIT_INSN(),
> +		},
> +		.fixup_map1 = { 9 },
> +		.fixup_map2 = { 3 },
> +		.result = ACCEPT,
> +		.prog_type = BPF_PROG_TYPE_TRACEPOINT,
> +	},
> +	{
> +		"map helper access to adjusted map (via const reg)",
> +		.insns = {
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +			BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 6),
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
> +			BPF_MOV64_IMM(BPF_REG_3,
> +				      offsetof(struct test_val, foo)),
> +			BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_EXIT_INSN(),
> +		},
> +		.fixup_map1 = { 10 },
> +		.fixup_map2 = { 3 },
> +		.result = ACCEPT,
> +		.prog_type = BPF_PROG_TYPE_TRACEPOINT,
> +	},
> +	{
> +		"map helper access to adjusted map (via variable)",
> +		.insns = {
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +			BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 7),
> +			BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
> +			BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_0, 0),
> +			BPF_JMP_IMM(BPF_JGT, BPF_REG_3,
> +				    offsetof(struct test_val, foo), 4),
> +			BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
> +			BPF_LD_MAP_FD(BPF_REG_1, 0),
> +			BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +			BPF_EXIT_INSN(),
> +		},
> +		.fixup_map1 = { 11 },
> +		.fixup_map2 = { 3 },
> +		.result = ACCEPT,
> +		.prog_type = BPF_PROG_TYPE_TRACEPOINT,
> +	},
> +	{
>  		"map element value is preserved across register spilling",
>  		.insns = {
>  			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> -- 
> 2.7.4
> 


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