This adds the Hornet Linux Security Module which provides signature verification of eBPF programs. This allows users to continue to maintain an invariant that all code running inside of the kernel has been signed.
The primary target for signature verification is light-skeleton based eBPF programs which was introduced here: https://lore.kernel.org/bpf/20220209054315.73833-1-alexei.starovoitov@gmail....
eBPF programs, before loading, undergo a complex set of operations which transform pseudo-values within the immediate operands of instructions into concrete values based on the running system. Typically, this is done by libbpf in userspace. Light-skeletons were introduced in order to support preloading of bpf programs and user-mode-drivers by removing the dependency on libbpf and userspace-based operations.
Userpace modifications, which may change every time a program gets loaded or runs on a slightly different kernel, break known signature verification algorithms. A method is needed for passing unadulterated binary buffers into the kernel in-order to use existing signature verification algorithms. Light-skeleton loaders with their support of only in-kernel relocations fit that constraint.
Hornet employs a signature verification scheme similar to that of kernel modules. A signature is appended to the end of an executable file. During an invocation of the BPF_PROG_LOAD subcommand, a signature is extracted from the current task's executable file. That signature is used to verify the integrity of the bpf instructions and maps which were passed into the kernel. Additionally, Hornet implicitly trusts any programs which were loaded from inside kernel rather than userspace, which allows BPF_PRELOAD programs along with outputs for BPF_SYSCALL programs to run.
The validation check consists of checking a PKCS#7 formatted signature against a data buffer containing the raw instructions of an eBPF program, followed by the initial values of any maps used by the program. Maps are verified to be frozen before signature verification checking to stop TOCTOU attacks.
Signed-off-by: Blaise Boscaccy bboscaccy@linux.microsoft.com --- Documentation/admin-guide/LSM/Hornet.rst | 65 ++++++ Documentation/admin-guide/LSM/index.rst | 1 + MAINTAINERS | 9 + crypto/asymmetric_keys/pkcs7_verify.c | 10 + include/linux/kernel_read_file.h | 1 + include/linux/verification.h | 1 + include/uapi/linux/lsm.h | 1 + security/Kconfig | 3 +- security/Makefile | 1 + security/hornet/Kconfig | 24 +++ security/hornet/Makefile | 4 + security/hornet/hornet_lsm.c | 250 +++++++++++++++++++++++ security/selinux/hooks.c | 12 +- security/selinux/include/classmap.h | 2 +- 14 files changed, 380 insertions(+), 4 deletions(-) create mode 100644 Documentation/admin-guide/LSM/Hornet.rst create mode 100644 security/hornet/Kconfig create mode 100644 security/hornet/Makefile create mode 100644 security/hornet/hornet_lsm.c
diff --git a/Documentation/admin-guide/LSM/Hornet.rst b/Documentation/admin-guide/LSM/Hornet.rst new file mode 100644 index 000000000000..a8109c2a5fdf --- /dev/null +++ b/Documentation/admin-guide/LSM/Hornet.rst @@ -0,0 +1,65 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====== +Hornet +====== + +Hornet is a Linux Security Module that provides signature verification +for eBPF programs. This is selectable at build-time with +``CONFIG_SECURITY_HORNET``. + +Overview +======== + +Hornet provides signature verification for eBPF programs by utilizing +the existing PKCS#7 infrastructure that's used for module signature +verification. Hornet works by creating a buffer containing the eBPF +program instructions along with its associated maps and checking a +signature against that buffer. The signature is appended to the end of +the lskel executable file and is extracted at runtime via +get_task_exe_file. Hornet works by hooking into the +security_bpf_prog_load hook. Load invocations that originate from the +kernel (bpf preload, results of bpf_syscall programs, etc.) are +allowed to run unconditionally. Calls that originate from userspace +require signature verification. If signature verification fails, the +program will fail to load. Maps are verified to be frozen before the +signature check to prevent TOCTOU exploits where a sufficiently +privileged user could rewrite map data between the calls to +BPF_PROG_LOAD and BPF_PROG_RUN. + +Instruction/Map Ordering +======================== + +Hornet supports both sparse-array based maps via map discovery along +with the newly added fd_array_cnt API for continuous map arrays. The +buffer used for signature verification is assumed to be the +instructions followed by all maps used, ordered by their index in +fd_array. + +Configuration Options +===================== + +Hornet provides a kconfig knob +CONFIG_SECURITY_HORNET_WHITELIST_PID_ONE. Enabling this will allow +bpf programs to be loaded from pid 1 without undergoing a signature +verification check. This option is not recommened for production +systems. + +Tooling +======= + +Some tooling is provided to aid with the development of signed eBPF +light-skeletons. + +extract-skel.sh +--------------- + +This shell script extracts the instructions and map data used by the +light skeleton from the autogenerated header file created by bpftool. + +sign-ebpf +--------- + +sign-ebpf works similarly to the sign-file script with one key +difference: it takes a separate input binary used for signature +verification and will append the signature to a different output file. diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst index b44ef68f6e4d..57f6e9fbe5fd 100644 --- a/Documentation/admin-guide/LSM/index.rst +++ b/Documentation/admin-guide/LSM/index.rst @@ -49,3 +49,4 @@ subdirectories. SafeSetID ipe landlock + Hornet diff --git a/MAINTAINERS b/MAINTAINERS index 3cbf9ac0d83f..f4123ed2fb1c 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -10855,6 +10855,15 @@ S: Maintained F: Documentation/devicetree/bindings/iio/pressure/honeywell,mprls0025pa.yaml F: drivers/iio/pressure/mprls0025pa*
+HORNET SECURITY MODULE +M: Blaise Boscaccy bboscaccy@linux.microsoft.com +L: linux-security-module@vger.kernel.org +S: Supported +T: git https://github.com/blaiseboscaccy/hornet.git +F: Documentation/admin-guide/LSM/Hornet.rst +F: scripts/hornet/ +F: security/hornet/ + HP BIOSCFG DRIVER M: Jorge Lopez jorge.lopez2@hp.com L: platform-driver-x86@vger.kernel.org diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c index f0d4ff3c20a8..1a5fbb361218 100644 --- a/crypto/asymmetric_keys/pkcs7_verify.c +++ b/crypto/asymmetric_keys/pkcs7_verify.c @@ -428,6 +428,16 @@ int pkcs7_verify(struct pkcs7_message *pkcs7, } /* Authattr presence checked in parser */ break; + case VERIFYING_EBPF_SIGNATURE: + if (pkcs7->data_type != OID_data) { + pr_warn("Invalid ebpf sig (not pkcs7-data)\n"); + return -EKEYREJECTED; + } + if (pkcs7->have_authattrs) { + pr_warn("Invalid ebpf sig (has authattrs)\n"); + return -EKEYREJECTED; + } + break; case VERIFYING_UNSPECIFIED_SIGNATURE: if (pkcs7->data_type != OID_data) { pr_warn("Invalid unspecified sig (not pkcs7-data)\n"); diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h index 90451e2e12bd..7ed9337be542 100644 --- a/include/linux/kernel_read_file.h +++ b/include/linux/kernel_read_file.h @@ -14,6 +14,7 @@ id(KEXEC_INITRAMFS, kexec-initramfs) \ id(POLICY, security-policy) \ id(X509_CERTIFICATE, x509-certificate) \ + id(EBPF, ebpf) \ id(MAX_ID, )
#define __fid_enumify(ENUM, dummy) READING_ ## ENUM, diff --git a/include/linux/verification.h b/include/linux/verification.h index 4f3022d081c3..812be8ad5f74 100644 --- a/include/linux/verification.h +++ b/include/linux/verification.h @@ -35,6 +35,7 @@ enum key_being_used_for { VERIFYING_KEXEC_PE_SIGNATURE, VERIFYING_KEY_SIGNATURE, VERIFYING_KEY_SELF_SIGNATURE, + VERIFYING_EBPF_SIGNATURE, VERIFYING_UNSPECIFIED_SIGNATURE, NR__KEY_BEING_USED_FOR }; diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h index 938593dfd5da..2ff9bcdd551e 100644 --- a/include/uapi/linux/lsm.h +++ b/include/uapi/linux/lsm.h @@ -65,6 +65,7 @@ struct lsm_ctx { #define LSM_ID_IMA 111 #define LSM_ID_EVM 112 #define LSM_ID_IPE 113 +#define LSM_ID_HORNET 114
/* * LSM_ATTR_XXX definitions identify different LSM attributes diff --git a/security/Kconfig b/security/Kconfig index 4816fc74f81e..5cd47bbff765 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -230,6 +230,7 @@ source "security/safesetid/Kconfig" source "security/lockdown/Kconfig" source "security/landlock/Kconfig" source "security/ipe/Kconfig" +source "security/hornet/Kconfig"
source "security/integrity/Kconfig"
@@ -273,7 +274,7 @@ config LSM default "landlock,lockdown,yama,loadpin,safesetid,apparmor,selinux,smack,tomoyo,ipe,bpf" if DEFAULT_SECURITY_APPARMOR default "landlock,lockdown,yama,loadpin,safesetid,tomoyo,ipe,bpf" if DEFAULT_SECURITY_TOMOYO default "landlock,lockdown,yama,loadpin,safesetid,ipe,bpf" if DEFAULT_SECURITY_DAC - default "landlock,lockdown,yama,loadpin,safesetid,selinux,smack,tomoyo,apparmor,ipe,bpf" + default "landlock,lockdown,yama,loadpin,safesetid,selinux,smack,tomoyo,apparmor,ipe,hornet,bpf" help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list, except for those with order diff --git a/security/Makefile b/security/Makefile index 22ff4c8bd8ce..e24bccd951f8 100644 --- a/security/Makefile +++ b/security/Makefile @@ -26,6 +26,7 @@ obj-$(CONFIG_CGROUPS) += device_cgroup.o obj-$(CONFIG_BPF_LSM) += bpf/ obj-$(CONFIG_SECURITY_LANDLOCK) += landlock/ obj-$(CONFIG_SECURITY_IPE) += ipe/ +obj-$(CONFIG_SECURITY_HORNET) += hornet/
# Object integrity file lists obj-$(CONFIG_INTEGRITY) += integrity/ diff --git a/security/hornet/Kconfig b/security/hornet/Kconfig new file mode 100644 index 000000000000..539503dafe94 --- /dev/null +++ b/security/hornet/Kconfig @@ -0,0 +1,24 @@ +# SPDX-License-Identifier: GPL-2.0-only +config SECURITY_HORNET + bool "Hornet support" + depends on SECURITY + default n + help + This selects Hornet. + Further information can be found in + Documentation/admin-guide/LSM/Hornet.rst. + + If you are unsure how to answer this question, answer N. + + +config SECURITY_HORNET_WHITELIST_PID_ONE + bool "Whiltelist unsigned eBPF programs from PID 1" + depends on SECURITY_HORNET + default n + help + Selecting this will configure Hornet to allow eBPF loaded from pid 1 + to load without a verification check. + Further information can be found in + Documentation/admin-guide/LSM/Hornet.rst. + + If you are unsure how to answer this question, answer N. diff --git a/security/hornet/Makefile b/security/hornet/Makefile new file mode 100644 index 000000000000..79f4657b215f --- /dev/null +++ b/security/hornet/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SECURITY_HORNET) := hornet.o + +hornet-y := hornet_lsm.o diff --git a/security/hornet/hornet_lsm.c b/security/hornet/hornet_lsm.c new file mode 100644 index 000000000000..012bb2dc45b2 --- /dev/null +++ b/security/hornet/hornet_lsm.c @@ -0,0 +1,250 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Hornet Linux Security Module + * + * Author: Blaise Boscaccy bboscaccy@linux.microsoft.com + * + * Copyright (C) 2025 Microsoft Corporation + */ + +#include <linux/lsm_hooks.h> +#include <uapi/linux/lsm.h> +#include <linux/bpf.h> +#include <linux/verification.h> +#include <crypto/public_key.h> +#include <linux/module_signature.h> +#include <crypto/pkcs7.h> +#include <linux/sort.h> + +#define EBPF_SIG_STRING "~eBPF signature appended~\n" +#define MAX_USED_MAPS 64 + +struct hornet_maps { + u32 used_idx[MAX_USED_MAPS]; + u32 used_map_cnt; + bpfptr_t fd_array; +}; + +static int cmp_idx(const void *a, const void *b) +{ + return *(const u32 *)a - *(const u32 *)b; +} + +static int add_used_map(struct hornet_maps *maps, int idx) +{ + int i; + + for (i = 0; i < maps->used_map_cnt; i++) + if (maps->used_idx[i] == idx) + return i; + + if (maps->used_map_cnt >= MAX_USED_MAPS) + return -E2BIG; + + maps->used_idx[maps->used_map_cnt] = idx; + return maps->used_map_cnt++; +} + +static int hornet_find_maps(struct bpf_prog *prog, struct hornet_maps *maps) +{ + struct bpf_insn *insn = prog->insnsi; + int insn_cnt = prog->len; + int i; + int err; + + for (i = 0; i < insn_cnt; i++, insn++) { + if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) { + switch (insn[0].src_reg) { + case BPF_PSEUDO_MAP_IDX_VALUE: + case BPF_PSEUDO_MAP_IDX: + err = add_used_map(maps, insn[0].imm); + if (err < 0) + return err; + break; + default: + break; + } + } + } + /* Sort the spare-array indices. This should match the map ordering used during + * signature generation + */ + sort(maps->used_idx, maps->used_map_cnt, sizeof(*maps->used_idx), + cmp_idx, NULL); + + return 0; +} + +static int hornet_populate_fd_array(struct hornet_maps *maps, u32 fd_array_cnt) +{ + int i; + + if (fd_array_cnt > MAX_USED_MAPS) + return -E2BIG; + + for (i = 0; i < fd_array_cnt; i++) + maps->used_idx[i] = i; + + maps->used_map_cnt = fd_array_cnt; + return 0; +} + +static int hornet_verify_lskel(struct bpf_prog *prog, struct hornet_maps *maps, + void *sig, size_t sig_len) +{ + int map_fd; + u32 i; + void *buf; + void *new; + size_t buf_sz; + struct bpf_map *map; + int err = 0; + int key = 0; + + buf = kmalloc_array(prog->len, sizeof(struct bpf_insn), GFP_KERNEL); + if (!buf) + return -ENOMEM; + buf_sz = prog->len * sizeof(struct bpf_insn); + memcpy(buf, prog->insnsi, buf_sz); + + for (i = 0; i < maps->used_map_cnt; i++) { + err = copy_from_bpfptr_offset(&map_fd, maps->fd_array, + maps->used_idx[i] * sizeof(map_fd), + sizeof(map_fd)); + if (err < 0) + continue; + + CLASS(fd, f)(map_fd); + if (fd_empty(f)) + continue; + if (unlikely(fd_file(f)->f_op != &bpf_map_fops)) + continue; + map = fd_file(f)->private_data; + + if (!map->frozen) { + err = -EINVAL; + goto out; + } + + new = krealloc(buf, buf_sz + map->value_size, GFP_KERNEL); + if (!new) { + err = -ENOMEM; + goto out; + } + buf = new; + new = map->ops->map_lookup_elem(map, &key); + if (!new) { + err = -ENOENT; + goto out; + } + memcpy(buf + buf_sz, new, map->value_size); + buf_sz += map->value_size; + } + + err = verify_pkcs7_signature(buf, buf_sz, sig, sig_len, + VERIFY_USE_SECONDARY_KEYRING, + VERIFYING_EBPF_SIGNATURE, + NULL, NULL); +out: + kfree(buf); + return err; +} + +static int hornet_check_binary(struct bpf_prog *prog, union bpf_attr *attr, + struct hornet_maps *maps) +{ + struct file *file; + const unsigned long markerlen = sizeof(EBPF_SIG_STRING) - 1; + void *buf = NULL; + size_t sz = 0, sig_len, prog_len, buf_sz; + int err = 0; + struct module_signature sig; + + file = get_task_exe_file(current); + if (!file) + return -1; + + buf_sz = kernel_read_file(file, 0, &buf, INT_MAX, &sz, READING_EBPF); + fput(file); + if (!buf_sz) + return -1; + + prog_len = buf_sz; + + if (prog_len > markerlen && + memcmp(buf + prog_len - markerlen, EBPF_SIG_STRING, markerlen) == 0) { + /* We truncate the program to discard the signature */ + prog_len -= markerlen; + if (prog_len < sizeof(sig)) { + err = -EINVAL; + goto out; + } + + memcpy(&sig, buf + (prog_len - sizeof(sig)), sizeof(sig)); + sig_len = be32_to_cpu(sig.sig_len); + prog_len -= sig_len + sizeof(sig); + + err = mod_check_sig(&sig, prog->len * sizeof(struct bpf_insn), "ebpf"); + if (err) + goto out; + + err = hornet_verify_lskel(prog, maps, buf + prog_len, sig_len); + } else { + err = -EINVAL; + } +out: + kvfree(buf); + return err; +} + +static int hornet_check_signature(struct bpf_prog *prog, union bpf_attr *attr, + struct bpf_token *token) +{ + struct hornet_maps maps = {0}; + int err; + + /* support both sparse arrays and explicit continuous arrays of map fds */ + if (attr->fd_array_cnt) + err = hornet_populate_fd_array(&maps, attr->fd_array_cnt); + else + err = hornet_find_maps(prog, &maps); + + if (err < 0) + return err; + + maps.fd_array = make_bpfptr(attr->fd_array, false); + return hornet_check_binary(prog, attr, &maps); +} + +static int hornet_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr, + struct bpf_token *token, bool is_kernel) +{ + if (is_kernel) + return 0; +#ifdef CONFIG_SECURITY_HORNET_WHITELIST_PID_ONE + if (current->pid == 1) + return 0; +#endif + return hornet_check_signature(prog, attr, token); +} + +static struct security_hook_list hornet_hooks[] __ro_after_init = { + LSM_HOOK_INIT(bpf_prog_load, hornet_bpf_prog_load), +}; + +static const struct lsm_id hornet_lsmid = { + .name = "hornet", + .id = LSM_ID_HORNET, +}; + +static int __init hornet_init(void) +{ + pr_info("Hornet: eBPF signature verification enabled\n"); + security_add_hooks(hornet_hooks, ARRAY_SIZE(hornet_hooks), &hornet_lsmid); + return 0; +} + +DEFINE_LSM(hornet) = { + .name = "hornet", + .init = hornet_init, +}; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index e7a7dcab81db..901fa6574083 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -4133,7 +4133,7 @@ static int selinux_kernel_read_file(struct file *file, { int rc = 0;
- BUILD_BUG_ON_MSG(READING_MAX_ID > 7, + BUILD_BUG_ON_MSG(READING_MAX_ID > 8, "New kernel_read_file_id introduced; update SELinux!");
switch (id) { @@ -4158,6 +4158,10 @@ static int selinux_kernel_read_file(struct file *file, rc = selinux_kernel_load_from_file(file, SYSTEM__X509_CERTIFICATE_LOAD); break; + case READING_EBPF: + rc = selinux_kernel_load_from_file(file, + SYSTEM__EBPF_LOAD); + break; default: break; } @@ -4169,7 +4173,7 @@ static int selinux_kernel_load_data(enum kernel_load_data_id id, bool contents) { int rc = 0;
- BUILD_BUG_ON_MSG(LOADING_MAX_ID > 7, + BUILD_BUG_ON_MSG(LOADING_MAX_ID > 8, "New kernel_load_data_id introduced; update SELinux!");
switch (id) { @@ -4195,6 +4199,10 @@ static int selinux_kernel_load_data(enum kernel_load_data_id id, bool contents) rc = selinux_kernel_load_from_file(NULL, SYSTEM__X509_CERTIFICATE_LOAD); break; + case LOADING_EBPF: + rc = selinux_kernel_load_from_file(NULL, + SYSTEM__EBPF_LOAD); + break; default: break; } diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index 04a9b480885e..671db23451df 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -65,7 +65,7 @@ const struct security_class_mapping secclass_map[] = { { "ipc_info", "syslog_read", "syslog_mod", "syslog_console", "module_request", "module_load", "firmware_load", "kexec_image_load", "kexec_initramfs_load", "policy_load", - "x509_certificate_load", NULL } }, + "x509_certificate_load", "ebpf_load", NULL } }, { "capability", { COMMON_CAP_PERMS, NULL } }, { "filesystem", { "mount", "remount", "unmount", "getattr", "relabelfrom",