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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <linux/libbpf.h>
#include "bpf-devices.h"
#include "bpf-program.h"
#define PASS_JUMP_OFF 4096
static int bpf_access_type(const char *acc) {
int r = 0;
assert(acc);
for (; *acc; acc++)
switch(*acc) {
case 'r':
r |= BPF_DEVCG_ACC_READ;
break;
case 'w':
r |= BPF_DEVCG_ACC_WRITE;
break;
case 'm':
r |= BPF_DEVCG_ACC_MKNOD;
break;
default:
return -EINVAL;
}
return r;
}
int cgroup_bpf_whitelist_device(BPFProgram *prog, int type, int major, int minor, const char *acc) {
struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 6), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 3), /* compare access type */
BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 2), /* compare major */
BPF_JMP_IMM(BPF_JNE, BPF_REG_5, minor, 1), /* compare minor */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
insn[2].imm = access;
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
int cgroup_bpf_whitelist_major(BPFProgram *prog, int type, int major, const char *acc) {
struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 2), /* compare access type */
BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 1), /* compare major */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
insn[2].imm = access;
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
int cgroup_bpf_whitelist_class(BPFProgram *prog, int type, const char *acc) {
struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 1), /* compare access type */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
insn[2].imm = access;
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
int cgroup_init_device_bpf(BPFProgram **ret, CGroupDevicePolicy policy, bool whitelist) {
struct bpf_insn pre_insn[] = {
/* load device type to r2 */
BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, access_type)),
/* load access type to r3 */
BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, access_type)),
BPF_ALU32_IMM(BPF_RSH, BPF_REG_3, 16),
/* load major number to r4 */
BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, major)),
/* load minor number to r5 */
BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, minor)),
};
_cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
int r;
assert(ret);
if (policy == CGROUP_AUTO && !whitelist)
return 0;
r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &prog);
if (r < 0)
return log_error_errno(r, "Loading device control BPF program failed: %m");
if (policy == CGROUP_CLOSED || whitelist) {
r = bpf_program_add_instructions(prog, pre_insn, ELEMENTSOF(pre_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
}
*ret = TAKE_PTR(prog);
return 0;
}
int cgroup_apply_device_bpf(Unit *u, BPFProgram *prog, CGroupDevicePolicy policy, bool whitelist) {
struct bpf_insn post_insn[] = {
/* return DENY */
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_JMP_A(1),
};
struct bpf_insn exit_insn[] = {
/* else return ALLOW */
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_EXIT_INSN()
};
_cleanup_free_ char *path = NULL;
int r;
if (!prog) {
/* Remove existing program. */
u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
return 0;
}
if (policy != CGROUP_STRICT || whitelist) {
size_t off;
r = bpf_program_add_instructions(prog, post_insn, ELEMENTSOF(post_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
/* Fixup PASS_JUMP_OFF jump offsets. */
for (off = 0; off < prog->n_instructions; off++) {
struct bpf_insn *ins = &prog->instructions[off];
if (ins->code == (BPF_JMP | BPF_JA) && ins->off == PASS_JUMP_OFF)
ins->off = prog->n_instructions - off - 1;
}
} else
/* Explicitly forbid everything. */
exit_insn[0].imm = 0;
r = bpf_program_add_instructions(prog, exit_insn, ELEMENTSOF(exit_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, NULL, &path);
if (r < 0)
return log_error_errno(r, "Failed to determine cgroup path: %m");
r = bpf_program_cgroup_attach(prog, BPF_CGROUP_DEVICE, path, BPF_F_ALLOW_MULTI);
if (r < 0)
return log_error_errno(r, "Attaching device control BPF program to cgroup %s failed: %m", path);
/* Unref the old BPF program (which will implicitly detach it) right before attaching the new program. */
u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
/* Remember that this BPF program is installed now. */
u->bpf_device_control_installed = bpf_program_ref(prog);
return 0;
}
int bpf_devices_supported(void) {
struct bpf_insn trivial[] = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_EXIT_INSN()
};
_cleanup_(bpf_program_unrefp) BPFProgram *program = NULL;
static int supported = -1;
int r;
/* Checks whether BPF device controller is supported. For this, we check five things:
*
* a) whether we are privileged
* b) whether the unified hierarchy is being used
* c) the BPF implementation in the kernel supports BPF_PROG_TYPE_CGROUP_DEVICE programs, which we require
*/
if (supported >= 0)
return supported;
if (geteuid() != 0) {
log_debug("Not enough privileges, BPF device control is not supported.");
return supported = 0;
}
r = cg_unified_controller(SYSTEMD_CGROUP_CONTROLLER);
if (r < 0)
return log_error_errno(r, "Can't determine whether the unified hierarchy is used: %m");
if (r == 0) {
log_debug("Not running with unified cgroups, BPF device control is not supported.");
return supported = 0;
}
r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &program);
if (r < 0) {
log_debug_errno(r, "Can't allocate CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
r = bpf_program_add_instructions(program, trivial, ELEMENTSOF(trivial));
if (r < 0) {
log_debug_errno(r, "Can't add trivial instructions to CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
r = bpf_program_load_kernel(program, NULL, 0);
if (r < 0) {
log_debug_errno(r, "Can't load kernel CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
return supported = 1;
}
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