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libbpf: Sanitize BPF program code for bpf_probe_read_{kernel, user}[_str]

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Add BPF program code sanitization pass, replacing calls to BPF
bpf_probe_read_{kernel,user}[_str]() helpers with bpf_probe_read[_str](), if
libbpf detects that kernel doesn't support new variants.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200818213356.2629020-5-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2020-08-18 14:33:53 -07:00 • committed by Alexei Starovoitov
parent bb180fb240
commit 109cea5a59
1 changed files with 80 additions and 0 deletions
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80
tools/lib/bpf/libbpf.c
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@ -180,6 +180,8 @@ enum kern_feature_id {
FEAT_ARRAY_MMAP, FEAT_ARRAY_MMAP,
/* kernel support for expected_attach_type in BPF_PROG_LOAD */ /* kernel support for expected_attach_type in BPF_PROG_LOAD */
FEAT_EXP_ATTACH_TYPE, FEAT_EXP_ATTACH_TYPE,
/* bpf_probe_read_{kernel,user}[_str] helpers */
FEAT_PROBE_READ_KERN,
__FEAT_CNT, __FEAT_CNT,
}; };
@ -3591,6 +3593,27 @@ static int probe_kern_exp_attach_type(void)
return probe_fd(bpf_load_program_xattr(&attr, NULL, 0)); return probe_fd(bpf_load_program_xattr(&attr, NULL, 0));
} }
static int probe_kern_probe_read_kernel(void)
{
struct bpf_load_program_attr attr;
struct bpf_insn insns[] = {
BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), /* r1 = r10 (fp) */
BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), /* r1 += -8 */
BPF_MOV64_IMM(BPF_REG_2, 8), /* r2 = 8 */
BPF_MOV64_IMM(BPF_REG_3, 0), /* r3 = 0 */
BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_probe_read_kernel),
BPF_EXIT_INSN(),
};
memset(&attr, 0, sizeof(attr));
attr.prog_type = BPF_PROG_TYPE_KPROBE;
attr.insns = insns;
attr.insns_cnt = ARRAY_SIZE(insns);
attr.license = "GPL";
return probe_fd(bpf_load_program_xattr(&attr, NULL, 0));
}
enum kern_feature_result { enum kern_feature_result {
FEAT_UNKNOWN = 0, FEAT_UNKNOWN = 0,
FEAT_SUPPORTED = 1, FEAT_SUPPORTED = 1,
@ -3626,6 +3649,9 @@ static struct kern_feature_desc {
"BPF_PROG_LOAD expected_attach_type attribute", "BPF_PROG_LOAD expected_attach_type attribute",
probe_kern_exp_attach_type, probe_kern_exp_attach_type,
}, },
[FEAT_PROBE_READ_KERN] = {
"bpf_probe_read_kernel() helper", probe_kern_probe_read_kernel,
}
}; };
static bool kernel_supports(enum kern_feature_id feat_id) static bool kernel_supports(enum kern_feature_id feat_id)
@ -5335,6 +5361,53 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
return 0; return 0;
} }
static bool insn_is_helper_call(struct bpf_insn *insn, enum bpf_func_id *func_id)
{
__u8 class = BPF_CLASS(insn->code);
if ((class == BPF_JMP || class == BPF_JMP32) &&
BPF_OP(insn->code) == BPF_CALL &&
BPF_SRC(insn->code) == BPF_K &&
insn->src_reg == 0 && insn->dst_reg == 0) {
if (func_id)
*func_id = insn->imm;
return true;
}
return false;
}
static int bpf_object__sanitize_prog(struct bpf_object* obj, struct bpf_program *prog)
{
struct bpf_insn *insn = prog->insns;
enum bpf_func_id func_id;
int i;
for (i = 0; i < prog->insns_cnt; i++, insn++) {
if (!insn_is_helper_call(insn, &func_id))
continue;
/* on kernels that don't yet support
* bpf_probe_read_{kernel,user}[_str] helpers, fall back
* to bpf_probe_read() which works well for old kernels
*/
switch (func_id) {
case BPF_FUNC_probe_read_kernel:
case BPF_FUNC_probe_read_user:
if (!kernel_supports(FEAT_PROBE_READ_KERN))
insn->imm = BPF_FUNC_probe_read;
break;
case BPF_FUNC_probe_read_kernel_str:
case BPF_FUNC_probe_read_user_str:
if (!kernel_supports(FEAT_PROBE_READ_KERN))
insn->imm = BPF_FUNC_probe_read_str;
break;
default:
break;
}
}
return 0;
}
static int static int
load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
char *license, __u32 kern_version, int *pfd) char *license, __u32 kern_version, int *pfd)
@ -5549,6 +5622,13 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
size_t i; size_t i;
int err; int err;
for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i];
err = bpf_object__sanitize_prog(obj, prog);
if (err)
return err;
}
for (i = 0; i < obj->nr_programs; i++) { for (i = 0; i < obj->nr_programs; i++) {
prog = &obj->programs[i]; prog = &obj->programs[i];
if (bpf_program__is_function_storage(prog, obj)) if (bpf_program__is_function_storage(prog, obj))