Compressed syscall database wtih O(1) lookup

libkafel.so 5x smaller (x86_64, stripped): down to 88KiB from 440KiB.

Closes google#20

Author: mejedi

src/Makefile

@@ -17,18 +17,14 @@
 #   limitations under the License.
 #
 
+SUBDIRS:=syscalls
+
 OBJCOPY?=objcopy
 
 CFLAGS+=-fPIC -fvisibility=hidden
-GENERATED_SRCS:=lexer.c parser.c
+GENERATED_SRCS:=lexer.c parser.c syscalldb.c
 GENERATED:=lexer.h parser.h ${GENERATED_SRCS}
-TEMPORARY:=libkafel_r.o libkafel.o
-SYSCALL_LISTS:=amd64_syscalls.c \
-               i386_syscalls.c \
-               aarch64_syscalls.c \
-               mipso32_syscalls.c \
-               mips64_syscalls.c \
-               arm_syscalls.c
+TEMPORARY:=libkafel_r.o libkafel.o syscalldb.gperf
 SRCS:=kafel.c \
       context.c \
       codegen.c \
@@ -37,8 +33,7 @@ SRCS:=kafel.c \
       policy.c \
       range_rules.c \
       syscall.c \
-      ${GENERATED_SRCS} \
-      $(SYSCALL_LISTS:%.c=syscalls/%.c)
+      ${GENERATED_SRCS}
 DYNAMIC_TARGET:=${PROJECT_ROOT}libkafel.so
 STATIC_TARGET:=${PROJECT_ROOT}libkafel.a
 TARGET=${DYNAMIC_TARGET} ${STATIC_TARGET}
@@ -65,6 +60,10 @@ lexer.h lexer.c: lexer.l
 parser.h parser.c: parser.y
 	bison $<
 
+syscalldb.c: syscalls
+	./syscalls/syscalldb_generator > ./syscalldb.gperf
+	gperf -m10 --output-file=./syscalldb.c ./syscalldb.gperf
+
 # DO NOT DELETE THIS LINE -- make depend depends on it.
 
 kafel.o: codegen.h context.h includes.h policy.h expression.h syscall.h
@@ -76,14 +75,9 @@ expression.o: expression.h common.h
 includes.o: includes.h common.h
 policy.o: policy.h expression.h common.h
 range_rules.o: range_rules.h policy.h expression.h common.h syscall.h
-syscall.o: syscall.h common.h
+syscall.o: syscall.h syscalldb.h common.h
+syscalldb.o: syscall.h syscalldb.h syscalldb.inl
 lexer.o: parser.h context.h includes.h policy.h expression.h syscall.h
 lexer.o: common.h
 parser.o: parser.h context.h includes.h policy.h expression.h syscall.h
 parser.o: lexer.h
-syscalls/amd64_syscalls.o: syscall.h
-syscalls/i386_syscalls.o: syscall.h
-syscalls/aarch64_syscalls.o: syscall.h
-syscalls/mipso32_syscalls.o: syscall.h
-syscalls/mips64_syscalls.o: syscall.h
-syscalls/arm_syscalls.o: syscall.h

src/context.c

@@ -70,7 +70,6 @@ void kafel_ctxt_reset(kafel_ctxt_t ctxt) {
   }
   ctxt->default_action = 0;
   ctxt->lexical_error = false;
-  ctxt->syscalls = NULL;
 }
 
 void kafel_ctxt_clean(kafel_ctxt_t ctxt) {

src/context.h

@@ -46,7 +46,7 @@ struct kafel_ctxt {
   struct policy* main_policy;
   int default_action;
   uint32_t target_arch;
-  const struct syscall_list* syscalls;
+  uint32_t target_arch_mask;
   struct {
     enum {
       INPUT_NONE,

src/kafel.c

@@ -57,8 +57,8 @@ static int parse(struct kafel_ctxt* ctxt) {
   kafel_yyset_column(1, scanner);
   kafel_yyset_lineno(1, scanner);
 
-  ctxt->syscalls = syscalls_lookup(ctxt->target_arch);
-  if (ctxt->syscalls == NULL) {
+  ctxt->target_arch_mask = syscall_get_arch_mask(ctxt->target_arch);
+  if (!ctxt->target_arch_mask) {
     append_error(ctxt, "Cannot resolve syscall list for architecture %#x\n",
                  ctxt->target_arch);
     kafel_yylex_destroy(scanner);

src/parser.y

@@ -298,7 +298,7 @@ syscall_id
                 $$ = syscall_custom(value);
             } else {
                 $$ = (struct syscall_descriptor*)
-                        syscall_lookup(ctxt->syscalls, $1);
+                        syscall_lookup(ctxt->target_arch_mask, $1);
                     if ($$ == NULL) {
                     emit_error(@1, "Undefined syscall `%s'", $1);
                     free($1); $1 = NULL;

src/syscall.c

@@ -25,75 +25,57 @@
 #include <string.h>
 
 #include "common.h"
+#include "syscalldb.h"
 
 // Fix for Linux <3.12
 #ifndef EM_ARM
 #define EM_ARM 40
 #endif
 
-#define SYSCALL_LIST_DECL(arch)                                 \
-  extern const struct syscall_descriptor arch##_syscall_list[]; \
-  extern const size_t arch##_syscall_list_size;
-
-#define SYSCALL_LIST(audit_arch, arch) \
-  { audit_arch, arch##_syscall_list, &arch##_syscall_list_size }
-
-SYSCALL_LIST_DECL(arm)
-SYSCALL_LIST_DECL(aarch64)
-SYSCALL_LIST_DECL(amd64)
-SYSCALL_LIST_DECL(mipso32)
-SYSCALL_LIST_DECL(mips64)
-SYSCALL_LIST_DECL(i386)
+struct syscall_descriptor* syscall_custom(uint32_t nr) {
+  struct syscall_descriptor* rv = calloc(1, sizeof(*rv));
+  rv->nr = nr;
+  return rv;
+}
 
-const struct syscall_list syscall_lists[] = {
+uint32_t syscall_get_arch_mask(uint32_t arch) {
+  switch (arch) {
+    default:
+      return 0;
 #ifdef AUDIT_ARCH_ARM
-    SYSCALL_LIST(AUDIT_ARCH_ARM, arm),
+    case AUDIT_ARCH_ARM:
+      return SYSCALLDB_ARCH_ARM_FLAG;
 #endif
 #ifdef AUDIT_ARCH_AARCH64
-    SYSCALL_LIST(AUDIT_ARCH_AARCH64, aarch64),
+    case AUDIT_ARCH_AARCH64:
+      return SYSCALLDB_ARCH_AARCH64_FLAG;
 #endif
 #ifdef AUDIT_ARCH_X86_64
-    SYSCALL_LIST(AUDIT_ARCH_X86_64, amd64),
+    case AUDIT_ARCH_X86_64:
+      return SYSCALLDB_ARCH_X86_64_FLAG;
 #endif
 #ifdef AUDIT_ARCH_MIPS
-    SYSCALL_LIST(AUDIT_ARCH_MIPS, mipso32),
+    case AUDIT_ARCH_MIPS:
+      return SYSCALLDB_ARCH_MIPS_FLAG;
 #endif
 #ifdef AUDIT_ARCH_MIPS64
-    SYSCALL_LIST(AUDIT_ARCH_MIPS64, mips64),
+    case AUDIT_ARCH_MIPS64:
+      return SYSCALLDB_ARCH_MIPS64_FLAG;
 #endif
 #ifdef AUDIT_ARCH_I386
-    SYSCALL_LIST(AUDIT_ARCH_I386, i386),
+    case AUDIT_ARCH_I386:
+      return SYSCALLDB_ARCH_I386_FLAG;
 #endif
-};
-
-struct syscall_descriptor* syscall_custom(uint32_t nr) {
-  struct syscall_descriptor* rv = calloc(1, sizeof(*rv));
-  rv->nr = nr;
-  rv->is_custom = true;
-  return rv;
-}
-
-const struct syscall_list* syscalls_lookup(uint32_t arch) {
-  for (size_t i = 0; i < sizeof(syscall_lists) / sizeof(syscall_lists[0]);
-       ++i) {
-    if (syscall_lists[i].arch == arch) {
-      return &syscall_lists[i];
-    }
   }
-  return NULL;
 }
 
-const struct syscall_descriptor* syscall_lookup(const struct syscall_list* list,
+const struct syscall_descriptor* syscall_lookup(uint32_t mask,
                                                 const char* name) {
-  ASSERT(list != NULL);
-  ASSERT(name != NULL);
-  /* TODO use binary search if syscalls can be guaranteed to be
-   *  sorted alphabetically
-   */
-  for (size_t i = 0; i < *list->size; ++i) {
-    if (strcmp(name, list->syscalls[i].name) == 0) {
-      return &list->syscalls[i];
-    }
+  const struct syscalldb_definition* def = syscalldb_lookup(name);
+  if (def && mask & def->arch_mask) {
+    struct syscall_descriptor* rv = calloc(1, sizeof(*rv));
+    syscalldb_unpack(def, mask, rv);
+    return rv;
   }
   return NULL;
 }
@@ -102,8 +84,6 @@ void syscall_descriptor_destroy(struct syscall_descriptor** desc) {
   ASSERT(desc != NULL);
   ASSERT((*desc) != NULL);
 
-  if ((*desc)->is_custom) {
-    free(*desc);
-  }
+  free(*desc);
   (*desc) = NULL;
 }

src/syscall.h

@@ -40,15 +40,9 @@ struct syscall_descriptor {
   struct syscall_arg args[SYSCALL_MAX_ARGS];
 };
 
-struct syscall_list {
-  uint32_t arch;
-  const struct syscall_descriptor* const syscalls;
-  const size_t* const size;
-};
-
 struct syscall_descriptor* syscall_custom(uint32_t nr);
-const struct syscall_list* syscalls_lookup(uint32_t arch);
-const struct syscall_descriptor* syscall_lookup(const struct syscall_list* list,
+uint32_t syscall_get_arch_mask(uint32_t arch);
+const struct syscall_descriptor* syscall_lookup(uint32_t arch_mask,
                                                 const char* name);
 void syscall_descriptor_destroy(struct syscall_descriptor** desc);
 

src/syscalldb.h

@@ -0,0 +1,115 @@
+/*
+   Kafel - syscall database
+   -----------------------------------------
+
+   Copyright 2019 Google Inc. All Rights Reserved.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+*/
+
+#ifndef KAFEL_SYSCALLDB_H
+#define KAFEL_SYSCALLDB_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+struct syscalldb_definition;
+struct syscall_descriptor;
+
+enum {
+  SYSCALLDB_ARCH_ARM_FLAG = 0x01,
+  SYSCALLDB_ARCH_AARCH64_FLAG = 0x02,
+  SYSCALLDB_ARCH_X86_64_FLAG = 0x04,
+  SYSCALLDB_ARCH_MIPS_FLAG = 0x08,
+  SYSCALLDB_ARCH_MIPS64_FLAG = 0x10,
+  SYSCALLDB_ARCH_I386_FLAG = 0x20,
+};
+
+const struct syscalldb_definition* syscalldb_lookup(const char* name);
+const char* syscalldb_reverse_lookup(uint32_t arch_mask, uint32_t nr);
+
+void syscalldb_unpack(const struct syscalldb_definition* definition,
+                      uint32_t arch_mask, struct syscall_descriptor* dest);
+
+/*
+   internals
+
+   Generated from individual syscall lists, has O(1) lookups and takes
+   advantage of the redundancy in the data set to reduce footprint
+   dramatically.
+
+   O(1) lookups are courtesy of the perfect hash function generated with
+   GNU gperf. PHF maps a name to an index in the table of <name, offset>
+   tuples. If names match, syscall definition is found at the given
+   offset.
+
+   Syscall definitions are of the variable length and stored back to
+   back. For details, consult syscalldb_definition struct.
+
+*/
+
+#define SYSCALLDB_MAX_ARGTYPE 8
+#define SYSCALLDB_MAX_ARGNAME 0xffff
+
+#define SYSCALLDB_ARGNO(no) (((uint32_t)(no)) << 24)
+#define SYSCALLDB_ARGTYPE(type) (((uint32_t)(type)) << 16)
+#define SYSCALLDB_ARGNAME(name) ((uint32_t)(name))
+
+#define SYSCALLDB_GET_ARGNO(x) (((x)&UINT32_C(0xff000000)) >> 24)
+#define SYSCALLDB_GET_ARGTYPE(x) (((x)&UINT32_C(0x00ff0000)) >> 16)
+#define SYSCALLDB_GET_ARGNAME(x) (((x)&UINT32_C(0x0000ffff)))
+
+struct syscalldb_entry {
+  uint16_t name;
+  uint16_t definition_offset;
+};
+
+/*
+  Observations:
+
+  (1) very few syscalls are arch-specific;
+
+  (2) syscall numbers varies wildly across archs;
+
+  (3) argument names and sizes (modulo pointer size differences) are the same
+      across archs with a few notable exceptions (ex: clone).
+
+  Last but not least, avoid pointers in static data structures with
+  initializers! Due to PIC requirements every single one of theese
+  require relocation. Increases the footprint and has runtime overhead.
+
+*/
+struct syscalldb_definition {
+  uint32_t arch_mask;  /* archs providing this syscall */
+  uint32_t n_arg_info; /* if >INT32_MAX), consult ext_arg_info;
+                                                  it has -n_arg_info entries */
+  union {
+    uint32_t arg_info[1]; /* argno, argtype, argname */
+    struct {
+      uint32_t arch_mask; /* archs this entry applies to */
+      uint32_t arg_info;  /* argno, argtype, argname */
+    } ext_arg_info[1];
+  };
+  /* uint32_t nr[]; syscall numbers, one value per a bit set in arch_mask */
+};
+
+#define SYSCALLDB_DEFINITION_NR(d) \
+  (&(d)->arch_mask + 2 +           \
+   ((d)->n_arg_info > INT32_MAX ? 2 * -(d)->n_arg_info : (d)->n_arg_info))
+
+#define SYSCALLDB_DEFINITION_NEXT(d) \
+  (typeof(d))(SYSCALLDB_DEFINITION_NR(d) + __builtin_popcount((d)->arch_mask))
+
+#endif /* KAFEL_SYSCALLDB_H */