On Fri, May 7, 2021 at 8:49 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Fix loader program to close temporary FDs when intermediate
> sys_bpf command fails.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
Looks good, but curious about 2 jumps vs 1 jump for cleanup
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> tools/lib/bpf/bpf_gen_internal.h | 1 +
> tools/lib/bpf/gen_loader.c | 38 ++++++++++++++++++++++++++++----
> 2 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
> index f42a55efd559..da2c026a3f31 100644
> --- a/tools/lib/bpf/bpf_gen_internal.h
> +++ b/tools/lib/bpf/bpf_gen_internal.h
> @@ -15,6 +15,7 @@ struct bpf_gen {
> void *data_cur;
> void *insn_start;
> void *insn_cur;
> + size_t cleanup_label;
> __u32 nr_progs;
> __u32 nr_maps;
> int log_level;
> diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
> index 585c672cc53e..b1709421ba90 100644
> --- a/tools/lib/bpf/gen_loader.c
> +++ b/tools/lib/bpf/gen_loader.c
> @@ -97,8 +97,36 @@ static void bpf_gen__emit2(struct bpf_gen *gen, struct bpf_insn insn1, struct bp
>
> void bpf_gen__init(struct bpf_gen *gen, int log_level)
> {
> + size_t stack_sz = sizeof(struct loader_stack);
> + int i;
> +
> gen->log_level = log_level;
> + /* save ctx pointer into R6 */
> bpf_gen__emit(gen, BPF_MOV64_REG(BPF_REG_6, BPF_REG_1));
> +
> + /* bzero stack */
> + bpf_gen__emit(gen, BPF_MOV64_REG(BPF_REG_1, BPF_REG_10));
> + bpf_gen__emit(gen, BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -stack_sz));
> + bpf_gen__emit(gen, BPF_MOV64_IMM(BPF_REG_2, stack_sz));
> + bpf_gen__emit(gen, BPF_MOV64_IMM(BPF_REG_3, 0));
> + bpf_gen__emit(gen, BPF_EMIT_CALL(BPF_FUNC_probe_read_kernel));
> +
> + /* jump over cleanup code */
> + bpf_gen__emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0,
> + /* size of cleanup code below */
> + (stack_sz / 4) * 3 + 2));
> +
> + /* remember the label where all error branches will jump to */
> + gen->cleanup_label = gen->insn_cur - gen->insn_start;
> + /* emit cleanup code: close all temp FDs */
> + for (i = 0; i < stack_sz; i+= 4) {
nit: checkpatch complains about missing space before +=
> + bpf_gen__emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_10, -stack_sz + i));
> + bpf_gen__emit(gen, BPF_JMP_IMM(BPF_JSLE, BPF_REG_1, 0, 1));
> + bpf_gen__emit(gen, BPF_EMIT_CALL(BPF_FUNC_sys_close));
> + }
> + /* R7 contains the error code from sys_bpf. Copy it into R0 and exit. */
> + bpf_gen__emit(gen, BPF_MOV64_REG(BPF_REG_0, BPF_REG_7));
> + bpf_gen__emit(gen, BPF_EXIT_INSN());
> }
>
> static int bpf_gen__add_data(struct bpf_gen *gen, const void *data, __u32 size)
> @@ -179,10 +207,12 @@ static void bpf_gen__emit_sys_bpf(struct bpf_gen *gen, int cmd, int attr, int at
>
> static void bpf_gen__emit_check_err(struct bpf_gen *gen)
> {
> - bpf_gen__emit(gen, BPF_JMP_IMM(BPF_JSGE, BPF_REG_7, 0, 2));
> - bpf_gen__emit(gen, BPF_MOV64_REG(BPF_REG_0, BPF_REG_7));
> - /* TODO: close intermediate FDs in case of error */
> - bpf_gen__emit(gen, BPF_EXIT_INSN());
> + /* R7 contains result of last sys_bpf command.
> + * if (R7 < 0) goto cleanup;
> + */
> + bpf_gen__emit(gen, BPF_JMP_IMM(BPF_JSGE, BPF_REG_7, 0, 1));
> + bpf_gen__emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0,
> + -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 1));
Just curious, why not a single BPF_JSLT straight to the cleanup label?
> }
>
> /* reg1 and reg2 should not be R1 - R5. They can be R0, R6 - R10 */
> --
> 2.30.2
>
