[v2,4/5] bpf: Add bpf_insn_buf, map and instruction concatenation helpers

Add helpers for building up programs. Tests before bpf_prog05 have not
been updated to use this for two reasons.

1. Some apply offsets to the map pointer returned or jump to the end
   of the program instead of just over an immediate exit
   instruction. Either way modifying them would require testing they
   still reproduce the bug.

2. Some have a lot of comments describing the program which is useful
   to learn from. These would need to be moved.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
---
 testcases/kernel/syscalls/bpf/bpf_common.c | 40 ++++++++++++++++++++++
 testcases/kernel/syscalls/bpf/bpf_common.h | 12 +++++++
 2 files changed, 52 insertions(+)

Hi!
> Add helpers for building up programs. Tests before bpf_prog05 have not
> been updated to use this for two reasons.
> 
> 1. Some apply offsets to the map pointer returned or jump to the end
>    of the program instead of just over an immediate exit
>    instruction. Either way modifying them would require testing they
>    still reproduce the bug.
> 
> 2. Some have a lot of comments describing the program which is useful
>    to learn from. These would need to be moved.
> 
> Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
> ---
>  testcases/kernel/syscalls/bpf/bpf_common.c | 40 ++++++++++++++++++++++
>  testcases/kernel/syscalls/bpf/bpf_common.h | 12 +++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/testcases/kernel/syscalls/bpf/bpf_common.c b/testcases/kernel/syscalls/bpf/bpf_common.c
> index b5337c22a..d80ed91bb 100644
> --- a/testcases/kernel/syscalls/bpf/bpf_common.c
> +++ b/testcases/kernel/syscalls/bpf/bpf_common.c
> @@ -82,6 +82,46 @@ long bpf_map_array_get(const int map_fd,
>  	return TST_RET;
>  }
>  
> +void bpf_insn_buf_cat(struct bpf_insn_buf *const self,
> +		      const struct bpf_insn *const insn_to_cat,
> +		      const size_t insn_to_cat_len)
> +{
> +	memcpy(((char *)self->insn) + self->byte_len,
> +	       insn_to_cat, insn_to_cat_len);
> +	self->byte_len += insn_to_cat_len;
> +}
> +
> +/* map[array_indx] = reg_to_save
> + *
> + * Inserts the following into insn_out.
> + *
> + * r1 = map_fd
> + * r2 = fp
> + * r2 = r2 - 4
> + * r2 = array_indx
> + * call map_lookup_elem(r1, r2)
> + * if r0 != 0 goto pc+1
> + * exit
> + * *r0 = reg_to_save
> + *
> + */
> + void bpf_insn_buf_array_set(struct bpf_insn_buf *const self, const int map_fd,
> +			     const uint32_t array_indx, const uint8_t reg_to_save)
> +{
> +	const struct bpf_insn map_insn[] = {
> +		BPF_LD_MAP_FD(BPF_REG_1, map_fd),
> +		BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +		BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
> +		BPF_ST_MEM(BPF_W, BPF_REG_2, 0, array_indx),
> +		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +		BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
> +		BPF_EXIT_INSN(),
> +		BPF_STX_MEM(BPF_DW, BPF_REG_0, reg_to_save, 0),
> +	};

I'm wondering if it would be easier to write a macro that would produce
this code, something as:

	#define BPF_ARRAY_STORE(map_fd, arr_idx, reg_to_save) \
		BPF_LD_MAP_FD(BPF_REG_1, map_fd), \
		BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), \
		BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), \
		BPF_ST_MEM(BPF_W, BPF_REG_2, 0, arr_indx), \
		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), \
		BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), \
		BPF_EXIT_INSN(), \
		BPF_STX_MEM(BPF_DW, BPF_REG_0, reg_to_save, 0)


Then we can use this piece as any other macros when constructing the
program, the only difference is that this macro emits 8 instructions
instead of one.

What do you think?

> +	bpf_insn_buf_cat(self, map_insn, sizeof(map_insn));
> +}
> +
>  void bpf_init_prog_attr(union bpf_attr *attr, const struct bpf_insn *prog,
>  	size_t prog_size, char *log_buf, size_t log_size)
>  {
> diff --git a/testcases/kernel/syscalls/bpf/bpf_common.h b/testcases/kernel/syscalls/bpf/bpf_common.h
> index 9e9935c2c..10b1eee86 100644
> --- a/testcases/kernel/syscalls/bpf/bpf_common.h
> +++ b/testcases/kernel/syscalls/bpf/bpf_common.h
> @@ -13,6 +13,11 @@
>  
>  #define BPF_MEMLOCK_ADD (2*1024*1024)
>  
> +struct bpf_insn_buf {
> +	size_t byte_len;
> +	struct bpf_insn insn[BPF_MAXINSNS];
> +};
> +
>  void rlimit_bump_memlock(void);
>  int bpf_map_create(union bpf_attr *attr);
>  int bpf_map_array_create(uint32_t max_entries);
> @@ -20,6 +25,13 @@ long bpf_map_array_get(const int map_fd,
>  		       const uint32_t *const array_indx,
>  		       uint64_t *const array_val);
>  
> +void bpf_insn_buf_cat(struct bpf_insn_buf *const self,
> +		      const struct bpf_insn *const insn_to_cat,
> +		      const size_t insn_to_cat_len);
> +void bpf_insn_buf_array_set(struct bpf_insn_buf *const self,
> +			    const int map_fd,
> +			    const uint32_t array_indx, const uint8_t reg_to_save);
> +
>  void bpf_init_prog_attr(union bpf_attr *attr, const struct bpf_insn *prog,
>  			size_t prog_size, char *log_buf, size_t log_size);
>  int bpf_load_prog(union bpf_attr *attr, const char *log);
> -- 
> 2.31.1
> 
> 
> -- 
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