execute: support syscall filtering using seccomp filters

src/shared/linux/seccomp-bpf.h

@@ -0,0 +1,76 @@
+/*
+ * seccomp example for x86 (32-bit and 64-bit) with BPF macros
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * Authors:
+ *  Will Drewry <wad@chromium.org>
+ *  Kees Cook <keescook@chromium.org>
+ *
+ * The code may be used by anyone for any purpose, and can serve as a
+ * starting point for developing applications using mode 2 seccomp.
+ */
+#ifndef _SECCOMP_BPF_H_
+#define _SECCOMP_BPF_H_
+
+#include <stdio.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/prctl.h>
+
+#include <linux/unistd.h>
+#include <linux/audit.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+
+#ifndef SECCOMP_MODE_FILTER
+# define SECCOMP_MODE_FILTER	2 /* uses user-supplied filter. */
+# define SECCOMP_RET_KILL	0x00000000U /* kill the task immediately */
+# define SECCOMP_RET_TRAP	0x00030000U /* disallow and force a SIGSYS */
+# define SECCOMP_RET_ALLOW	0x7fff0000U /* allow */
+struct seccomp_data {
+    int nr;
+    __u32 arch;
+    __u64 instruction_pointer;
+    __u64 args[6];
+};
+#endif
+#ifndef SYS_SECCOMP
+# define SYS_SECCOMP 1
+#endif
+
+#define syscall_nr (offsetof(struct seccomp_data, nr))
+#define arch_nr (offsetof(struct seccomp_data, arch))
+
+#if defined(__i386__)
+# define REG_SYSCALL	REG_EAX
+# define ARCH_NR	AUDIT_ARCH_I386
+#elif defined(__x86_64__)
+# define REG_SYSCALL	REG_RAX
+# define ARCH_NR	AUDIT_ARCH_X86_64
+#else
+# warning "Platform does not support seccomp filter yet"
+# define REG_SYSCALL	0
+# define ARCH_NR	0
+#endif
+
+#define VALIDATE_ARCHITECTURE \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, arch_nr), \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ARCH_NR, 1, 0), \
+	BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
+
+#define EXAMINE_SYSCALL \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr)
+
+#define ALLOW_SYSCALL(name) \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_##name, 0, 1), \
+	BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
+
+#define _KILL_PROCESS \
+	BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
+
+#endif /* _SECCOMP_BPF_H_ */

src/shared/linux/seccomp.h

@@ -0,0 +1,47 @@
+#ifndef _LINUX_SECCOMP_H
+#define _LINUX_SECCOMP_H
+
+
+#include <linux/types.h>
+
+
+/* Valid values for seccomp.mode and prctl(PR_SET_SECCOMP, <mode>) */
+#define SECCOMP_MODE_DISABLED	0 /* seccomp is not in use. */
+#define SECCOMP_MODE_STRICT	1 /* uses hard-coded filter. */
+#define SECCOMP_MODE_FILTER	2 /* uses user-supplied filter. */
+
+/*
+ * All BPF programs must return a 32-bit value.
+ * The bottom 16-bits are for optional return data.
+ * The upper 16-bits are ordered from least permissive values to most.
+ *
+ * The ordering ensures that a min_t() over composed return values always
+ * selects the least permissive choice.
+ */
+#define SECCOMP_RET_KILL	0x00000000U /* kill the task immediately */
+#define SECCOMP_RET_TRAP	0x00030000U /* disallow and force a SIGSYS */
+#define SECCOMP_RET_ERRNO	0x00050000U /* returns an errno */
+#define SECCOMP_RET_TRACE	0x7ff00000U /* pass to a tracer or disallow */
+#define SECCOMP_RET_ALLOW	0x7fff0000U /* allow */
+
+/* Masks for the return value sections. */
+#define SECCOMP_RET_ACTION	0x7fff0000U
+#define SECCOMP_RET_DATA	0x0000ffffU
+
+/**
+ * struct seccomp_data - the format the BPF program executes over.
+ * @nr: the system call number
+ * @arch: indicates system call convention as an AUDIT_ARCH_* value
+ *        as defined in <linux/audit.h>.
+ * @instruction_pointer: at the time of the system call.
+ * @args: up to 6 system call arguments always stored as 64-bit values
+ *        regardless of the architecture.
+ */
+struct seccomp_data {
+	int nr;
+	__u32 arch;
+	__u64 instruction_pointer;
+	__u64 args[6];
+};
+
+#endif /* _LINUX_SECCOMP_H */