Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/seccomp-bpf/codegen_unittest.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/seccomp-bpf/codegen.h"
+
+#include <errno.h>
+#include <linux/filter.h>
+
+#include <set>
+#include <string>
+#include <vector>
+
+#include "sandbox/linux/seccomp-bpf/basicblock.h"
+#include "sandbox/linux/seccomp-bpf/errorcode.h"
+#include "sandbox/linux/seccomp-bpf/instruction.h"
+#include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
+#include "sandbox/linux/tests/unit_tests.h"
+
+namespace sandbox {
+
+// We want to access some of the private methods in the code generator. We
+// do so by defining a "friend" that makes these methods public for us.
+class CodeGenUnittestHelper : public CodeGen {
+ public:
+  void FindBranchTargets(const Instruction& instructions,
+                         BranchTargets* branch_targets) {
+    CodeGen::FindBranchTargets(instructions, branch_targets);
+  }
+
+  BasicBlock* CutGraphIntoBasicBlocks(Instruction* insns,
+                                      const BranchTargets& branch_targets,
+                                      TargetsToBlocks* blocks) {
+    return CodeGen::CutGraphIntoBasicBlocks(insns, branch_targets, blocks);
+  }
+
+  void MergeTails(TargetsToBlocks* blocks) { CodeGen::MergeTails(blocks); }
+};
+
+enum { NO_FLAGS = 0x0000, HAS_MERGEABLE_TAILS = 0x0001, };
+
+Instruction* SampleProgramOneInstruction(CodeGen* codegen, int* flags) {
+  // Create the most basic valid BPF program:
+  //    RET 0
+  *flags = NO_FLAGS;
+  return codegen->MakeInstruction(BPF_RET + BPF_K, 0);
+}
+
+Instruction* SampleProgramSimpleBranch(CodeGen* codegen, int* flags) {
+  // Create a program with a single branch:
+  //    JUMP if eq 42 then $0 else $1
+  // 0: RET 1
+  // 1: RET 0
+  *flags = NO_FLAGS;
+  return codegen->MakeInstruction(
+      BPF_JMP + BPF_JEQ + BPF_K,
+      42,
+      codegen->MakeInstruction(BPF_RET + BPF_K, 1),
+      codegen->MakeInstruction(BPF_RET + BPF_K, 0));
+}
+
+Instruction* SampleProgramAtypicalBranch(CodeGen* codegen, int* flags) {
+  // Create a program with a single branch:
+  //    JUMP if eq 42 then $0 else $0
+  // 0: RET 0
+
+  // N.B.: As the instructions in both sides of the branch are already
+  //       the same object, we do not actually have any "mergeable" branches.
+  //       This needs to be reflected in our choice of "flags".
+  *flags = NO_FLAGS;
+
+  Instruction* ret = codegen->MakeInstruction(
+      BPF_RET + BPF_K, 0);
+  return codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 42, ret, ret);
+}
+
+Instruction* SampleProgramComplex(CodeGen* codegen, int* flags) {
+  // Creates a basic BPF program that we'll use to test some of the code:
+  //    JUMP if eq 42 the $0 else $1     (insn6)
+  // 0: LD 23                            (insn5)
+  // 1: JUMP if eq 42 then $2 else $4    (insn4)
+  // 2: JUMP to $3                       (insn2)
+  // 3: LD 42                            (insn1)
+  //    RET 42                           (insn0)
+  // 4: LD 42                            (insn3)
+  //    RET 42                           (insn3+)
+  *flags = HAS_MERGEABLE_TAILS;
+
+  Instruction* insn0 = codegen->MakeInstruction(BPF_RET + BPF_K, 42);
+  SANDBOX_ASSERT(insn0);
+  SANDBOX_ASSERT(insn0->code == BPF_RET + BPF_K);
+  SANDBOX_ASSERT(insn0->next == NULL);
+
+  Instruction* insn1 =
+      codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 42, insn0);
+  SANDBOX_ASSERT(insn1);
+  SANDBOX_ASSERT(insn1->code == BPF_LD + BPF_W + BPF_ABS);
+  SANDBOX_ASSERT(insn1->k == 42);
+  SANDBOX_ASSERT(insn1->next == insn0);
+
+  Instruction* insn2 = codegen->MakeInstruction(BPF_JMP + BPF_JA, 0, insn1);
+  SANDBOX_ASSERT(insn2);
+  SANDBOX_ASSERT(insn2->code == BPF_JMP + BPF_JA);
+  SANDBOX_ASSERT(insn2->jt_ptr == insn1);
+
+  // We explicitly duplicate instructions so that MergeTails() can coalesce
+  // them later.
+  Instruction* insn3 = codegen->MakeInstruction(
+      BPF_LD + BPF_W + BPF_ABS,
+      42,
+      codegen->MakeInstruction(BPF_RET + BPF_K, 42));
+
+  Instruction* insn4 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 42, insn2, insn3);
+  SANDBOX_ASSERT(insn4);
+  SANDBOX_ASSERT(insn4->code == BPF_JMP + BPF_JEQ + BPF_K);
+  SANDBOX_ASSERT(insn4->k == 42);
+  SANDBOX_ASSERT(insn4->jt_ptr == insn2);
+  SANDBOX_ASSERT(insn4->jf_ptr == insn3);
+
+  Instruction* insn5 =
+      codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 23, insn4);
+  SANDBOX_ASSERT(insn5);
+  SANDBOX_ASSERT(insn5->code == BPF_LD + BPF_W + BPF_ABS);
+  SANDBOX_ASSERT(insn5->k == 23);
+  SANDBOX_ASSERT(insn5->next == insn4);
+
+  // Force a basic block that ends in neither a jump instruction nor a return
+  // instruction. It only contains "insn5". This exercises one of the less
+  // common code paths in the topo-sort algorithm.
+  // This also gives us a diamond-shaped pattern in our graph, which stresses
+  // another aspect of the topo-sort algorithm (namely, the ability to
+  // correctly count the incoming branches for subtrees that are not disjunct).
+  Instruction* insn6 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 42, insn5, insn4);
+
+  return insn6;
+}
+
+Instruction* SampleProgramConfusingTails(CodeGen* codegen, int* flags) {
+  // This simple program demonstrates https://crbug.com/351103/
+  // The two "LOAD 0" instructions are blocks of their own. MergeTails() could
+  // be tempted to merge them since they are the same. However, they are
+  // not mergeable because they fall-through to non semantically equivalent
+  // blocks.
+  // Without the fix for this bug, this program should trigger the check in
+  // CompileAndCompare: the serialized graphs from the program and its compiled
+  // version will differ.
+  //
+  //  0) LOAD 1  // ???
+  //  1) if A == 0x1; then JMP 2 else JMP 3
+  //  2) LOAD 0  // System call number
+  //  3) if A == 0x2; then JMP 4 else JMP 5
+  //  4) LOAD 0  // System call number
+  //  5) if A == 0x1; then JMP 6 else JMP 7
+  //  6) RET 0
+  //  7) RET 1
+  *flags = NO_FLAGS;
+
+  Instruction* i7 = codegen->MakeInstruction(BPF_RET + BPF_K, 1);
+  Instruction* i6 = codegen->MakeInstruction(BPF_RET + BPF_K, 0);
+  Instruction* i5 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 1, i6, i7);
+  Instruction* i4 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 0, i5);
+  Instruction* i3 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 2, i4, i5);
+  Instruction* i2 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 0, i3);
+  Instruction* i1 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 1, i2, i3);
+  Instruction* i0 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 1, i1);
+
+  return i0;
+}
+
+Instruction* SampleProgramConfusingTailsBasic(CodeGen* codegen, int* flags) {
+  // Without the fix for https://crbug.com/351103/, (see
+  // SampleProgramConfusingTails()), this would generate a cyclic graph and
+  // crash as the two "LOAD 0" instructions would get merged.
+  //
+  // 0) LOAD 1  // ???
+  // 1) if A == 0x1; then JMP 2 else JMP 3
+  // 2) LOAD 0  // System call number
+  // 3) if A == 0x2; then JMP 4 else JMP 5
+  // 4) LOAD 0  // System call number
+  // 5) RET 1
+  *flags = NO_FLAGS;
+
+  Instruction* i5 = codegen->MakeInstruction(BPF_RET + BPF_K, 1);
+  Instruction* i4 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 0, i5);
+  Instruction* i3 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 2, i4, i5);
+  Instruction* i2 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 0, i3);
+  Instruction* i1 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 1, i2, i3);
+  Instruction* i0 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 1, i1);
+
+  return i0;
+}
+
+Instruction* SampleProgramConfusingTailsMergeable(CodeGen* codegen,
+                                                  int* flags) {
+  // This is similar to SampleProgramConfusingTails(), except that
+  // instructions 2 and 4 are now RET instructions.
+  // In PointerCompare(), this exercises the path where two blocks are of the
+  // same length and identical and the last instruction is a JMP or RET, so the
+  // following blocks don't need to be looked at and the blocks are mergeable.
+  //
+  // 0) LOAD 1  // ???
+  // 1) if A == 0x1; then JMP 2 else JMP 3
+  // 2) RET 42
+  // 3) if A == 0x2; then JMP 4 else JMP 5
+  // 4) RET 42
+  // 5) if A == 0x1; then JMP 6 else JMP 7
+  // 6) RET 0
+  // 7) RET 1
+  *flags = HAS_MERGEABLE_TAILS;
+
+  Instruction* i7 = codegen->MakeInstruction(BPF_RET + BPF_K, 1);
+  Instruction* i6 = codegen->MakeInstruction(BPF_RET + BPF_K, 0);
+  Instruction* i5 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 1, i6, i7);
+  Instruction* i4 = codegen->MakeInstruction(BPF_RET + BPF_K, 42);
+  Instruction* i3 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 2, i4, i5);
+  Instruction* i2 = codegen->MakeInstruction(BPF_RET + BPF_K, 42);
+  Instruction* i1 =
+      codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 1, i2, i3);
+  Instruction* i0 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 1, i1);
+
+  return i0;
+}
+void ForAllPrograms(void (*test)(CodeGenUnittestHelper*, Instruction*, int)) {
+  Instruction* (*function_table[])(CodeGen* codegen, int* flags) = {
+    SampleProgramOneInstruction,
+    SampleProgramSimpleBranch,
+    SampleProgramAtypicalBranch,
+    SampleProgramComplex,
+    SampleProgramConfusingTails,
+    SampleProgramConfusingTailsBasic,
+    SampleProgramConfusingTailsMergeable,
+  };
+
+  for (size_t i = 0; i < arraysize(function_table); ++i) {
+    CodeGenUnittestHelper codegen;
+    int flags = NO_FLAGS;
+    Instruction *prg = function_table[i](&codegen, &flags);
+    test(&codegen, prg, flags);
+  }
+}
+
+void MakeInstruction(CodeGenUnittestHelper* codegen,
+                     Instruction* program, int) {
+  // Nothing to do here
+}
+
+SANDBOX_TEST(CodeGen, MakeInstruction) {
+  ForAllPrograms(MakeInstruction);
+}
+
+void FindBranchTargets(CodeGenUnittestHelper* codegen, Instruction* prg, int) {
+  BranchTargets branch_targets;
+  codegen->FindBranchTargets(*prg, &branch_targets);
+
+  // Verifying the general properties that should be true for every
+  // well-formed BPF program.
+  // Perform a depth-first traversal of the BPF program an verify that all
+  // targets of BPF_JMP instructions are represented in the "branch_targets".
+  // At the same time, compute a set of both the branch targets and all the
+  // instructions in the program.
+  std::vector<Instruction*> stack;
+  std::set<Instruction*> all_instructions;
+  std::set<Instruction*> target_instructions;
+  BranchTargets::const_iterator end = branch_targets.end();
+  for (Instruction* insn = prg;;) {
+    all_instructions.insert(insn);
+    if (BPF_CLASS(insn->code) == BPF_JMP) {
+      target_instructions.insert(insn->jt_ptr);
+      SANDBOX_ASSERT(insn->jt_ptr != NULL);
+      SANDBOX_ASSERT(branch_targets.find(insn->jt_ptr) != end);
+      if (BPF_OP(insn->code) != BPF_JA) {
+        target_instructions.insert(insn->jf_ptr);
+        SANDBOX_ASSERT(insn->jf_ptr != NULL);
+        SANDBOX_ASSERT(branch_targets.find(insn->jf_ptr) != end);
+        stack.push_back(insn->jf_ptr);
+      }
+      insn = insn->jt_ptr;
+    } else if (BPF_CLASS(insn->code) == BPF_RET) {
+      SANDBOX_ASSERT(insn->next == NULL);
+      if (stack.empty()) {
+        break;
+      }
+      insn = stack.back();
+      stack.pop_back();
+    } else {
+      SANDBOX_ASSERT(insn->next != NULL);
+      insn = insn->next;
+    }
+  }
+  SANDBOX_ASSERT(target_instructions.size() == branch_targets.size());
+
+  // We can now subtract the set of the branch targets from the set of all
+  // instructions. This gives us a set with the instructions that nobody
+  // ever jumps to. Verify that they are no included in the
+  // "branch_targets" that FindBranchTargets() computed for us.
+  Instructions non_target_instructions(all_instructions.size() -
+                                       target_instructions.size());
+  set_difference(all_instructions.begin(),
+                 all_instructions.end(),
+                 target_instructions.begin(),
+                 target_instructions.end(),
+                 non_target_instructions.begin());
+  for (Instructions::const_iterator iter = non_target_instructions.begin();
+       iter != non_target_instructions.end();
+       ++iter) {
+    SANDBOX_ASSERT(branch_targets.find(*iter) == end);
+  }
+}
+
+SANDBOX_TEST(CodeGen, FindBranchTargets) { ForAllPrograms(FindBranchTargets); }
+
+void CutGraphIntoBasicBlocks(CodeGenUnittestHelper* codegen,
+                             Instruction* prg,
+                             int) {
+  BranchTargets branch_targets;
+  codegen->FindBranchTargets(*prg, &branch_targets);
+  TargetsToBlocks all_blocks;
+  BasicBlock* first_block =
+      codegen->CutGraphIntoBasicBlocks(prg, branch_targets, &all_blocks);
+  SANDBOX_ASSERT(first_block != NULL);
+  SANDBOX_ASSERT(first_block->instructions.size() > 0);
+  Instruction* first_insn = first_block->instructions[0];
+
+  // Basic blocks are supposed to start with a branch target and end with
+  // either a jump or a return instruction. It can also end, if the next
+  // instruction forms the beginning of a new basic block. There should be
+  // no other jumps or return instructions in the middle of a basic block.
+  for (TargetsToBlocks::const_iterator bb_iter = all_blocks.begin();
+       bb_iter != all_blocks.end();
+       ++bb_iter) {
+    BasicBlock* bb = bb_iter->second;
+    SANDBOX_ASSERT(bb != NULL);
+    SANDBOX_ASSERT(bb->instructions.size() > 0);
+    Instruction* insn = bb->instructions[0];
+    SANDBOX_ASSERT(insn == first_insn ||
+                   branch_targets.find(insn) != branch_targets.end());
+    for (Instructions::const_iterator insn_iter = bb->instructions.begin();;) {
+      insn = *insn_iter;
+      if (++insn_iter != bb->instructions.end()) {
+        SANDBOX_ASSERT(BPF_CLASS(insn->code) != BPF_JMP);
+        SANDBOX_ASSERT(BPF_CLASS(insn->code) != BPF_RET);
+      } else {
+        SANDBOX_ASSERT(BPF_CLASS(insn->code) == BPF_JMP ||
+                       BPF_CLASS(insn->code) == BPF_RET ||
+                       branch_targets.find(insn->next) != branch_targets.end());
+        break;
+      }
+      SANDBOX_ASSERT(branch_targets.find(*insn_iter) == branch_targets.end());
+    }
+  }
+}
+
+SANDBOX_TEST(CodeGen, CutGraphIntoBasicBlocks) {
+  ForAllPrograms(CutGraphIntoBasicBlocks);
+}
+
+void MergeTails(CodeGenUnittestHelper* codegen, Instruction* prg, int flags) {
+  BranchTargets branch_targets;
+  codegen->FindBranchTargets(*prg, &branch_targets);
+  TargetsToBlocks all_blocks;
+  BasicBlock* first_block =
+      codegen->CutGraphIntoBasicBlocks(prg, branch_targets, &all_blocks);
+
+  // The shape of our graph and thus the function of our program should
+  // still be unchanged after we run MergeTails(). We verify this by
+  // serializing the graph and verifying that it is still the same.
+  // We also verify that at least some of the edges changed because of
+  // tail merging.
+  std::string graph[2];
+  std::string edges[2];
+
+  // The loop executes twice. After the first run, we call MergeTails() on
+  // our graph.
+  for (int i = 0;;) {
+    // Traverse the entire program in depth-first order.
+    std::vector<BasicBlock*> stack;
+    for (BasicBlock* bb = first_block;;) {
+      // Serialize the instructions in this basic block. In general, we only
+      // need to serialize "code" and "k"; except for a BPF_JA instruction
+      // where "k" isn't set.
+      // The stream of instructions should be unchanged after MergeTails().
+      for (Instructions::const_iterator iter = bb->instructions.begin();
+           iter != bb->instructions.end();
+           ++iter) {
+        graph[i].append(reinterpret_cast<char*>(&(*iter)->code),
+                        sizeof((*iter)->code));
+        if (BPF_CLASS((*iter)->code) != BPF_JMP ||
+            BPF_OP((*iter)->code) != BPF_JA) {
+          graph[i].append(reinterpret_cast<char*>(&(*iter)->k),
+                          sizeof((*iter)->k));
+        }
+      }
+
+      // Also serialize the addresses the basic blocks as we encounter them.
+      // This will change as basic blocks are coalesed by MergeTails().
+      edges[i].append(reinterpret_cast<char*>(&bb), sizeof(bb));
+
+      // Depth-first traversal of the graph. We only ever need to look at the
+      // very last instruction in the basic block, as that is the only one that
+      // can change code flow.
+      Instruction* insn = bb->instructions.back();
+      if (BPF_CLASS(insn->code) == BPF_JMP) {
+        // For jump instructions, we need to remember the "false" branch while
+        // traversing the "true" branch. This is not necessary for BPF_JA which
+        // only has a single branch.
+        if (BPF_OP(insn->code) != BPF_JA) {
+          stack.push_back(all_blocks[insn->jf_ptr]);
+        }
+        bb = all_blocks[insn->jt_ptr];
+      } else if (BPF_CLASS(insn->code) == BPF_RET) {
+        // After a BPF_RET, see if we need to back track.
+        if (stack.empty()) {
+          break;
+        }
+        bb = stack.back();
+        stack.pop_back();
+      } else {
+        // For "normal" instructions, just follow to the next basic block.
+        bb = all_blocks[insn->next];
+      }
+    }
+
+    // Our loop runs exactly two times.
+    if (++i > 1) {
+      break;
+    }
+    codegen->MergeTails(&all_blocks);
+  }
+  SANDBOX_ASSERT(graph[0] == graph[1]);
+  if (flags & HAS_MERGEABLE_TAILS) {
+    SANDBOX_ASSERT(edges[0] != edges[1]);
+  } else {
+    SANDBOX_ASSERT(edges[0] == edges[1]);
+  }
+}
+
+SANDBOX_TEST(CodeGen, MergeTails) {
+  ForAllPrograms(MergeTails);
+}
+
+void CompileAndCompare(CodeGenUnittestHelper* codegen, Instruction* prg, int) {
+  // TopoSortBasicBlocks() has internal checks that cause it to fail, if it
+  // detects a problem. Typically, if anything goes wrong, this looks to the
+  // TopoSort algorithm as if there had been cycles in the input data.
+  // This provides a pretty good unittest.
+  // We hand-crafted the program returned by SampleProgram() to exercise
+  // several of the more interesting code-paths. See comments in
+  // SampleProgram() for details.
+  // In addition to relying on the internal consistency checks in the compiler,
+  // we also serialize the graph and the resulting BPF program and compare
+  // them. With the exception of BPF_JA instructions that might have been
+  // inserted, both instruction streams should be equivalent.
+  // As Compile() modifies the instructions, we have to serialize the graph
+  // before calling Compile().
+  std::string source;
+  Instructions source_stack;
+  for (const Instruction* insn = prg, *next; insn; insn = next) {
+    if (BPF_CLASS(insn->code) == BPF_JMP) {
+      if (BPF_OP(insn->code) == BPF_JA) {
+        // Do not serialize BPF_JA instructions (see above).
+        next = insn->jt_ptr;
+        continue;
+      } else {
+        source_stack.push_back(insn->jf_ptr);
+        next = insn->jt_ptr;
+      }
+    } else if (BPF_CLASS(insn->code) == BPF_RET) {
+      if (source_stack.empty()) {
+        next = NULL;
+      } else {
+        next = source_stack.back();
+        source_stack.pop_back();
+      }
+    } else {
+      next = insn->next;
+    }
+    // Only serialize "code" and "k". That's all the information we need to
+    // compare. The rest of the information is encoded in the order of
+    // instructions.
+    source.append(reinterpret_cast<const char*>(&insn->code),
+                  sizeof(insn->code));
+    source.append(reinterpret_cast<const char*>(&insn->k), sizeof(insn->k));
+  }
+
+  // Compile the program
+  CodeGen::Program bpf;
+  codegen->Compile(prg, &bpf);
+
+  // Serialize the resulting BPF instructions.
+  std::string assembly;
+  std::vector<int> assembly_stack;
+  for (int idx = 0; idx >= 0;) {
+    SANDBOX_ASSERT(idx < (int)bpf.size());
+    struct sock_filter& insn = bpf[idx];
+    if (BPF_CLASS(insn.code) == BPF_JMP) {
+      if (BPF_OP(insn.code) == BPF_JA) {
+        // Do not serialize BPF_JA instructions (see above).
+        idx += insn.k + 1;
+        continue;
+      } else {
+        assembly_stack.push_back(idx + insn.jf + 1);
+        idx += insn.jt + 1;
+      }
+    } else if (BPF_CLASS(insn.code) == BPF_RET) {
+      if (assembly_stack.empty()) {
+        idx = -1;
+      } else {
+        idx = assembly_stack.back();
+        assembly_stack.pop_back();
+      }
+    } else {
+      ++idx;
+    }
+    // Serialize the same information that we serialized before compilation.
+    assembly.append(reinterpret_cast<char*>(&insn.code), sizeof(insn.code));
+    assembly.append(reinterpret_cast<char*>(&insn.k), sizeof(insn.k));
+  }
+  SANDBOX_ASSERT(source == assembly);
+}
+
+SANDBOX_TEST(CodeGen, All) {
+  ForAllPrograms(CompileAndCompare);
+}
+
+}  // namespace sandbox