diff options
Diffstat (limited to 'src/core/bpf-devices.c')
| -rw-r--r-- | src/core/bpf-devices.c | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/src/core/bpf-devices.c b/src/core/bpf-devices.c new file mode 100644 index 0000000..81e91fc --- /dev/null +++ b/src/core/bpf-devices.c @@ -0,0 +1,270 @@ +/* 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; +} |