summaryrefslogtreecommitdiffstats
path: root/src/core/bpf-devices.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/core/bpf-devices.c')
-rw-r--r--src/core/bpf-devices.c270
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;
+}