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Commit a5f20640 authored by mdempsky's avatar mdempsky Committed by Commit bot
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Decouple CodeGen from ErrorCode 

CodeGen's only dependency on ErrorCode was one MakeInstruction()
overload, which can be removed by making the caller responsible for
converting the ErrorCode to a BPF_RET'able value. Fortunately, there
are only two uses of this function:

1. SandboxBPF::RetExpression() which is easily fixed by simply calling
ErrorCode::err() to get the ErrorCode's error value.

2. codegen_unittest.cc which is merely testing the BPF code generator,
and so any return values will do: no need to be seccomp-bpf return
values... so just replace them with simple integer values.  (While
here, change a few bare "BPF_RET" arguments to "BPF_RET + BPF_K" just
to be consistent.)

After this CL, CodeGen focuses solely on assembling programs for the
abstract BPF machine, while higher-level abstractions (primarily
SandboxBPF) are responsible for using it in a way that's semantically
meaningful for seccomp-bpf.

BUG=414363

Review URL: https://codereview.chromium.org/576673003

Cr-Commit-Position: refs/heads/master@{#295192}
parent d117e910
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Showing with 36 additions and 46 deletions
sandbox/linux/seccomp-bpf/codegen.cc
View file @ a5f20640
......@@ -172,17 +172,6 @@ Instruction* CodeGen::MakeInstruction(uint16_t code,
}
}
Instruction* CodeGen::MakeInstruction(uint16_t code, const ErrorCode& err) {
if (BPF_CLASS(code) != BPF_RET) {
SANDBOX_DIE("ErrorCodes can only be used in return expressions");
}
if (err.error_type_ != ErrorCode::ET_SIMPLE &&
err.error_type_ != ErrorCode::ET_TRAP) {
SANDBOX_DIE("ErrorCode is not suitable for returning from a BPF program");
}
return MakeInstruction(code, err.err_);
}
Instruction* CodeGen::MakeInstruction(uint16_t code,
uint32_t k,
Instruction* jt,
......
sandbox/linux/seccomp-bpf/codegen.h
View file @ a5f20640
......@@ -13,7 +13,6 @@
namespace sandbox {
struct BasicBlock;
class ErrorCode;
struct Instruction;
typedef std::vector<Instruction*> Instructions;
......@@ -43,7 +42,8 @@ typedef std::map<const BasicBlock*, int> IncomingBranches;
// gen.MakeInstruction(BPF_JMP+BPF_EQ+BPF_K, __NR_getpid,
// Trap(GetPidHandler, NULL), NULL);
// gen.JoinInstructions(branch,
// gen.MakeInstruction(BPF_RET+BPF_K, ErrorCode(ErrorCode::ERR_ALLOWED)));
// gen.MakeInstruction(BPF_RET+BPF_K,
// ErrorCode(ErrorCode::ERR_ALLOWED).err()));
//
// // Simplified code follows; in practice, it is important to avoid calling
// // any C++ destructors after starting the sandbox.
......@@ -69,7 +69,6 @@ class SANDBOX_EXPORT CodeGen {
Instruction* MakeInstruction(uint16_t code,
uint32_t k,
Instruction* next = NULL);
Instruction* MakeInstruction(uint16_t code, const ErrorCode& err);
Instruction* MakeInstruction(uint16_t code,
uint32_t k,
Instruction* jt,
......
sandbox/linux/seccomp-bpf/codegen_unittest.cc
View file @ a5f20640
......@@ -46,30 +46,28 @@ enum { NO_FLAGS = 0x0000, HAS_MERGEABLE_TAILS = 0x0001, };
Instruction* SampleProgramOneInstruction(CodeGen* codegen, int* flags) {
// Create the most basic valid BPF program:
// RET ERR_ALLOWED
// RET 0
*flags = NO_FLAGS;
return codegen->MakeInstruction(BPF_RET + BPF_K,
ErrorCode(ErrorCode::ERR_ALLOWED));
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 EPERM
// 1: RET ERR_ALLOWED
// 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, ErrorCode(EPERM)),
codegen->MakeInstruction(BPF_RET + BPF_K,
ErrorCode(ErrorCode::ERR_ALLOWED)));
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 ERR_ALLOWED
// 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.
......@@ -77,7 +75,7 @@ Instruction* SampleProgramAtypicalBranch(CodeGen* codegen, int* flags) {
*flags = NO_FLAGS;
Instruction* ret = codegen->MakeInstruction(
BPF_RET + BPF_K, ErrorCode(ErrorCode::ERR_ALLOWED));
BPF_RET + BPF_K, 0);
return codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 42, ret, ret);
}
......@@ -88,9 +86,9 @@ Instruction* SampleProgramComplex(CodeGen* codegen, int* flags) {
// 1: JUMP if eq 42 then $2 else $4 (insn4)
// 2: JUMP to $3 (insn1)
// 3: LD 42 (insn0)
// RET ErrorCode(42) (insn2)
// RET 42 (insn2)
// 4: LD 42 (insn3)
// RET ErrorCode(42) (insn3+)
// RET 42 (insn3+)
*flags = HAS_MERGEABLE_TAILS;
Instruction* insn0 = codegen->MakeInstruction(BPF_LD + BPF_W + BPF_ABS, 42);
......@@ -104,7 +102,7 @@ Instruction* SampleProgramComplex(CodeGen* codegen, int* flags) {
SANDBOX_ASSERT(insn1->code == BPF_JMP + BPF_JA);
SANDBOX_ASSERT(insn1->jt_ptr == insn0);
Instruction* insn2 = codegen->MakeInstruction(BPF_RET + BPF_K, ErrorCode(42));
Instruction* insn2 = codegen->MakeInstruction(BPF_RET + BPF_K, 42);
SANDBOX_ASSERT(insn2);
SANDBOX_ASSERT(insn2->code == BPF_RET + BPF_K);
SANDBOX_ASSERT(insn2->next == NULL);
......@@ -114,7 +112,7 @@ Instruction* SampleProgramComplex(CodeGen* codegen, int* flags) {
Instruction* insn3 = codegen->MakeInstruction(
BPF_LD + BPF_W + BPF_ABS,
42,
codegen->MakeInstruction(BPF_RET + BPF_K, ErrorCode(42)));
codegen->MakeInstruction(BPF_RET + BPF_K, 42));
Instruction* insn4 =
codegen->MakeInstruction(BPF_JMP + BPF_JEQ + BPF_K, 42, insn1, insn3);
......@@ -162,12 +160,12 @@ Instruction* SampleProgramConfusingTails(CodeGen* codegen, int* flags) {
// 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 0x50000 // errno = 0
// 7) RET 0x50001 // errno = 1
// 6) RET 0
// 7) RET 1
*flags = NO_FLAGS;
Instruction* i7 = codegen->MakeInstruction(BPF_RET, ErrorCode(1));
Instruction* i6 = codegen->MakeInstruction(BPF_RET, ErrorCode(0));
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);
......@@ -191,10 +189,10 @@ Instruction* SampleProgramConfusingTailsBasic(CodeGen* codegen, int* flags) {
// 2) LOAD 0 // System call number
// 3) if A == 0x2; then JMP 4 else JMP 5
// 4) LOAD 0 // System call number
// 5) RET 0x50001 // errno = 1
// 5) RET 1
*flags = NO_FLAGS;
Instruction* i5 = codegen->MakeInstruction(BPF_RET, ErrorCode(1));
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);
......@@ -216,22 +214,22 @@ Instruction* SampleProgramConfusingTailsMergeable(CodeGen* codegen,
//
// 0) LOAD 1 // ???
// 1) if A == 0x1; then JMP 2 else JMP 3
// 2) RET 0x5002a // errno = 42
// 2) RET 42
// 3) if A == 0x2; then JMP 4 else JMP 5
// 4) RET 0x5002a // errno = 42
// 4) RET 42
// 5) if A == 0x1; then JMP 6 else JMP 7
// 6) RET 0x50000 // errno = 0
// 7) RET 0x50001 // errno = 1
// 6) RET 0
// 7) RET 1
*flags = HAS_MERGEABLE_TAILS;
Instruction* i7 = codegen->MakeInstruction(BPF_RET, ErrorCode(1));
Instruction* i6 = codegen->MakeInstruction(BPF_RET, ErrorCode(0));
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, ErrorCode(42));
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, ErrorCode(42));
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);
......
sandbox/linux/seccomp-bpf/sandbox_bpf.cc
View file @ a5f20640
......@@ -888,10 +888,14 @@ Instruction* SandboxBPF::AssembleJumpTable(CodeGen* gen,
}
Instruction* SandboxBPF::RetExpression(CodeGen* gen, const ErrorCode& err) {
if (err.error_type_ == ErrorCode::ET_COND) {
return CondExpression(gen, err);
} else {
return gen->MakeInstruction(BPF_RET + BPF_K, err);
switch (err.error_type()) {
case ErrorCode::ET_COND:
return CondExpression(gen, err);
case ErrorCode::ET_SIMPLE:
case ErrorCode::ET_TRAP:
return gen->MakeInstruction(BPF_RET + BPF_K, err.err());
default:
SANDBOX_DIE("ErrorCode is not suitable for returning from a BPF program");
}
}
......
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