bpf: Add bpf_bprm_opts_set helper

.travis.yml

@@ -0,0 +1,33 @@
+sudo: required
+language: bash
+dist: bionic
+services:
+    - docker
+
+env:
+    global:
+        - PROJECT_NAME='libbpf'
+        - AUTHOR_EMAIL="$(git log -1 --pretty=\"%aE\")"
+        - REPO_ROOT="$TRAVIS_BUILD_DIR"
+        - CI_ROOT="$REPO_ROOT/travis-ci"
+        - VMTEST_ROOT="$CI_ROOT/vmtest"
+
+addons:
+    apt:
+        packages:
+            - qemu-kvm
+            - zstd
+            - binutils-dev
+            - elfutils
+            - libcap-dev
+            - libelf-dev
+            - libdw-dev
+            - python3-docutils
+
+jobs:
+    include:
+        - stage: Builds & Tests
+          name: Kernel LATEST + selftests
+          language: bash
+          env: KERNEL=LATEST
+          script:  $CI_ROOT/vmtest/run_vmtest.sh || travis_terminate 1

include/uapi/linux/bpf.h

@@ -3787,6 +3787,16 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)
+ *	Description
+ *		Set or clear certain options on *bprm*:
+ *
+ *		**BPF_F_BPRM_SECUREEXEC** Set the secureexec bit
+ *		which sets the **AT_SECURE** auxv for glibc. The bit
+ *		is cleared if the flag is not specified.
+ *	Return
+ *		**-EINVAL** if invalid *flags* are passed, zero otherwise.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3958,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(bprm_opts_set),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4130,11 @@ enum bpf_lwt_encap_mode {
 	BPF_LWT_ENCAP_IP,
 };
 
+/* Flags for bpf_bprm_opts_set helper */
+enum {
+	BPF_F_BPRM_SECUREEXEC	= (1ULL << 0),
+};
+
 #define __bpf_md_ptr(type, name)	\
 union {					\
 	type name;			\

kernel/bpf/bpf_lsm.c

@@ -7,6 +7,7 @@
 #include <linux/filter.h>
 #include <linux/bpf.h>
 #include <linux/btf.h>
+#include <linux/binfmts.h>
 #include <linux/lsm_hooks.h>
 #include <linux/bpf_lsm.h>
 #include <linux/kallsyms.h>
@@ -51,6 +52,29 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
 	return 0;
 }
 
+/* Mask for all the currently supported BPRM option flags */
+#define BPF_F_BRPM_OPTS_MASK	BPF_F_BPRM_SECUREEXEC
+
+BPF_CALL_2(bpf_bprm_opts_set, struct linux_binprm *, bprm, u64, flags)
+{
+	if (flags & ~BPF_F_BRPM_OPTS_MASK)
+		return -EINVAL;
+
+	bprm->secureexec = (flags & BPF_F_BPRM_SECUREEXEC);
+	return 0;
+}
+
+BTF_ID_LIST_SINGLE(bpf_bprm_opts_set_btf_ids, struct, linux_binprm)
+
+const static struct bpf_func_proto bpf_bprm_opts_set_proto = {
+	.func		= bpf_bprm_opts_set,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &bpf_bprm_opts_set_btf_ids[0],
+	.arg2_type	= ARG_ANYTHING,
+};
+
 static const struct bpf_func_proto *
 bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -71,6 +95,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_task_storage_get_proto;
 	case BPF_FUNC_task_storage_delete:
 		return &bpf_task_storage_delete_proto;
+	case BPF_FUNC_bprm_opts_set:
+		return &bpf_bprm_opts_set_proto;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}

scripts/bpf_helpers_doc.py

@@ -418,6 +418,7 @@ class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',
@@ -465,6 +466,7 @@ class PrinterHelpers(Printer):
             'struct bpf_tcp_sock',
             'struct bpf_tunnel_key',
             'struct bpf_xfrm_state',
+            'struct linux_binprm',
             'struct pt_regs',
             'struct sk_reuseport_md',
             'struct sockaddr',

tools/include/uapi/linux/bpf.h

@@ -3787,6 +3787,16 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)
+ *	Description
+ *		Set or clear certain options on *bprm*:
+ *
+ *		**BPF_F_BPRM_SECUREEXEC** Set the secureexec bit
+ *		which sets the **AT_SECURE** auxv for glibc. The bit
+ *		is cleared if the flag is not specified.
+ *	Return
+ *		**-EINVAL** if invalid *flags* are passed, zero otherwise.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3958,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(bprm_opts_set),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4130,11 @@ enum bpf_lwt_encap_mode {
 	BPF_LWT_ENCAP_IP,
 };
 
+/* Flags for bpf_bprm_opts_set helper */
+enum {
+	BPF_F_BPRM_SECUREEXEC	= (1ULL << 0),
+};
+
 #define __bpf_md_ptr(type, name)	\
 union {					\
 	type name;			\

tools/testing/selftests/bpf/prog_tests/test_bprm_opts.c

@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+
+#include <test_progs.h>
+#include <linux/limits.h>
+
+#include "bprm_opts.skel.h"
+#include "network_helpers.h"
+
+#ifndef __NR_pidfd_open
+#define __NR_pidfd_open 434
+#endif
+
+static const char * const bash_envp[] = { "TMPDIR=shouldnotbeset", NULL };
+
+static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
+{
+	return syscall(__NR_pidfd_open, pid, flags);
+}
+
+static int update_storage(int map_fd, int secureexec)
+{
+	int task_fd, ret = 0;
+
+	task_fd = sys_pidfd_open(getpid(), 0);
+	if (task_fd < 0)
+		return errno;
+
+	ret = bpf_map_update_elem(map_fd, &task_fd, &secureexec, BPF_NOEXIST);
+	if (ret)
+		ret = errno;
+
+	close(task_fd);
+	return ret;
+}
+
+static int run_set_secureexec(int map_fd, int secureexec)
+{
+	int child_pid, child_status, ret, null_fd;
+
+	child_pid = fork();
+	if (child_pid == 0) {
+		null_fd = open("/dev/null", O_WRONLY);
+		if (null_fd == -1)
+			exit(errno);
+		dup2(null_fd, STDOUT_FILENO);
+		dup2(null_fd, STDERR_FILENO);
+		close(null_fd);
+
+		/* Ensure that all executions from hereon are
+		 * secure by setting a local storage which is read by
+		 * the bprm_creds_for_exec hook and sets bprm->secureexec.
+		 */
+		ret = update_storage(map_fd, secureexec);
+		if (ret)
+			exit(ret);
+
+		/* If the binary is executed with securexec=1, the dynamic
+		 * loader ingores and unsets certain variables like LD_PRELOAD,
+		 * TMPDIR etc. TMPDIR is used here to simplify the example, as
+		 * LD_PRELOAD requires a real .so file.
+		 *
+		 * If the value of TMPDIR is set, the bash command returns 10
+		 * and if the value is unset, it returns 20.
+		 */
+		execle("/bin/bash", "bash", "-c",
+		       "[[ -z \"${TMPDIR}\" ]] || exit 10 && exit 20", NULL,
+		       bash_envp);
+		exit(errno);
+	} else if (child_pid > 0) {
+		waitpid(child_pid, &child_status, 0);
+		ret = WEXITSTATUS(child_status);
+
+		/* If a secureexec occurred, the exit status should be 20 */
+		if (secureexec && ret == 20)
+			return 0;
+
+		/* If normal execution happened, the exit code should be 10 */
+		if (!secureexec && ret == 10)
+			return 0;
+	}
+
+	return -EINVAL;
+}
+
+void test_test_bprm_opts(void)
+{
+	int err, duration = 0;
+	struct bprm_opts *skel = NULL;
+
+	skel = bprm_opts__open_and_load();
+	if (CHECK(!skel, "skel_load", "skeleton failed\n"))
+		goto close_prog;
+
+	err = bprm_opts__attach(skel);
+	if (CHECK(err, "attach", "attach failed: %d\n", err))
+		goto close_prog;
+
+	/* Run the test with the secureexec bit unset */
+	err = run_set_secureexec(bpf_map__fd(skel->maps.secure_exec_task_map),
+				 0 /* secureexec */);
+	if (CHECK(err, "run_set_secureexec:0", "err = %d\n", err))
+		goto close_prog;
+
+	/* Run the test with the secureexec bit set */
+	err = run_set_secureexec(bpf_map__fd(skel->maps.secure_exec_task_map),
+				 1 /* secureexec */);
+	if (CHECK(err, "run_set_secureexec:1", "err = %d\n", err))
+		goto close_prog;
+
+close_prog:
+	bprm_opts__destroy(skel);
+}

tools/testing/selftests/bpf/progs/bprm_opts.c

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2020 Google LLC.
+ */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, int);
+} secure_exec_task_map SEC(".maps");
+
+SEC("lsm/bprm_creds_for_exec")
+int BPF_PROG(secure_exec, struct linux_binprm *bprm)
+{
+	int *secureexec;
+
+	secureexec = bpf_task_storage_get(&secure_exec_task_map,
+				   bpf_get_current_task_btf(), 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+
+	if (secureexec && *secureexec)
+		bpf_bprm_opts_set(bprm, BPF_F_BPRM_SECUREEXEC);
+
+	return 0;
+}