| /* |
| * Copyright (C) 2016 Apple Inc. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY |
| * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR |
| * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY |
| * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #include "config.h" |
| #include "ShadowChicken.h" |
| |
| #include "JSCInlines.h" |
| #include "ShadowChickenInlines.h" |
| #include <wtf/ListDump.h> |
| |
| namespace JSC { |
| |
| static const bool verbose = false; |
| |
| void ShadowChicken::Packet::dump(PrintStream& out) const |
| { |
| if (!*this) { |
| out.print("empty"); |
| return; |
| } |
| |
| if (isPrologue()) { |
| out.print( |
| "{callee = ", RawPointer(callee), ", frame = ", RawPointer(frame), ", callerFrame = ", |
| RawPointer(callerFrame), "}"); |
| return; |
| } |
| |
| if (isTail()) { |
| out.print("tail:{frame = ", RawPointer(frame), "}"); |
| return; |
| } |
| |
| ASSERT(isThrow()); |
| out.print("throw"); |
| } |
| |
| void ShadowChicken::Frame::dump(PrintStream& out) const |
| { |
| out.print( |
| "{callee = ", RawPointer(callee), ", frame = ", RawPointer(frame), ", isTailDeleted = ", |
| isTailDeleted, "}"); |
| } |
| |
| ShadowChicken::ShadowChicken() |
| : m_logSize(Options::shadowChickenLogSize()) |
| { |
| m_log = static_cast<Packet*>(fastZeroedMalloc(sizeof(Packet) * m_logSize)); |
| m_logCursor = m_log; |
| m_logEnd = m_log + m_logSize; |
| } |
| |
| ShadowChicken::~ShadowChicken() |
| { |
| fastFree(m_log); |
| } |
| |
| void ShadowChicken::log(VM& vm, ExecState* exec, const Packet& packet) |
| { |
| update(vm, exec); |
| *m_logCursor++ = packet; |
| } |
| |
| void ShadowChicken::update(VM&, ExecState* exec) |
| { |
| if (verbose) { |
| dataLog("Running update on: ", *this, "\n"); |
| WTFReportBacktrace(); |
| } |
| |
| const unsigned logCursorIndex = m_logCursor - m_log; |
| |
| // We need to figure out how to reconcile the current machine stack with our shadow stack. We do |
| // that by figuring out how much of the shadow stack to pop. We apply three different rules. The |
| // precise rule relies on the log. The log contains caller frames, which means that we know |
| // where we bottomed out after making any call. If we bottomed out but made no calls then 'exec' |
| // will tell us. That's why "highestPointSinceLastTime" will go no lower than exec. The third |
| // rule, based on comparing to the current real stack, is executed in a later loop. |
| CallFrame* highestPointSinceLastTime = exec; |
| for (unsigned i = logCursorIndex; i--;) { |
| Packet packet = m_log[i]; |
| if (packet.isPrologue()) { |
| CallFrame* watermark; |
| if (i && m_log[i - 1].isTail()) |
| watermark = packet.frame; |
| else |
| watermark = packet.callerFrame; |
| highestPointSinceLastTime = std::max(highestPointSinceLastTime, watermark); |
| } |
| } |
| |
| if (verbose) |
| dataLog(" Highest point since last time: ", RawPointer(highestPointSinceLastTime), "\n"); |
| |
| while (!m_stack.isEmpty() && m_stack.last().frame < highestPointSinceLastTime) |
| m_stack.removeLast(); |
| |
| if (verbose) |
| dataLog(" Revised stack: ", listDump(m_stack), "\n"); |
| |
| // It's possible that the top of stack is now tail-deleted. The stack no longer contains any |
| // frames below the log's high watermark. That means that we just need to look for the first |
| // occurence of a tail packet for the current stack top. |
| if (!m_stack.isEmpty()) { |
| ASSERT(!m_stack.last().isTailDeleted); |
| for (unsigned i = 0; i < logCursorIndex; ++i) { |
| Packet& packet = m_log[i]; |
| if (packet.isTail() && packet.frame == m_stack.last().frame) { |
| m_stack.last().isTailDeleted = true; |
| break; |
| } |
| } |
| } |
| |
| if (verbose) |
| dataLog(" Revised stack: ", listDump(m_stack), "\n"); |
| |
| // The log-based and exec-based rules require that ShadowChicken was enabled. The point of |
| // ShadowChicken is to give sensible-looking results even if we had not logged. This means that |
| // we need to reconcile the shadow stack and the real stack by actually looking at the real |
| // stack. This reconciliation allows the shadow stack to have extra tail-deleted frames, but it |
| // forbids it from diverging from the real stack on normal frames. |
| if (!m_stack.isEmpty()) { |
| Vector<Frame> stackRightNow; |
| StackVisitor::visit( |
| exec, [&] (StackVisitor& visitor) -> StackVisitor::Status { |
| if (visitor->isInlinedFrame()) |
| return StackVisitor::Continue; |
| bool isTailDeleted = false; |
| stackRightNow.append(Frame(visitor->callee(), visitor->callFrame(), isTailDeleted)); |
| return StackVisitor::Continue; |
| }); |
| stackRightNow.reverse(); |
| |
| if (verbose) |
| dataLog(" Stack right now: ", listDump(stackRightNow), "\n"); |
| |
| unsigned shadowIndex = 0; |
| unsigned rightNowIndex = 0; |
| while (shadowIndex < m_stack.size() && rightNowIndex < stackRightNow.size()) { |
| if (m_stack[shadowIndex].isTailDeleted) { |
| shadowIndex++; |
| continue; |
| } |
| if (m_stack[shadowIndex] == stackRightNow[rightNowIndex]) { |
| shadowIndex++; |
| rightNowIndex++; |
| continue; |
| } |
| break; |
| } |
| m_stack.resize(shadowIndex); |
| |
| if (verbose) |
| dataLog(" Revised stack: ", listDump(m_stack), "\n"); |
| } |
| |
| // It's possible that the top stack frame is actually lower than highestPointSinceLastTime. |
| // Account for that here. |
| highestPointSinceLastTime = nullptr; |
| for (unsigned i = m_stack.size(); i--;) { |
| if (!m_stack[i].isTailDeleted) { |
| highestPointSinceLastTime = m_stack[i].frame; |
| break; |
| } |
| } |
| |
| if (verbose) |
| dataLog(" Highest point since last time: ", RawPointer(highestPointSinceLastTime), "\n"); |
| |
| // Set everything up so that we know where the top frame is in the log. |
| unsigned indexInLog = logCursorIndex; |
| |
| auto advanceIndexInLogTo = |
| [&] (CallFrame* frame, JSObject* callee, CallFrame* callerFrame) -> bool { |
| if (verbose) |
| dataLog(" Advancing to frame = ", RawPointer(frame), " from indexInLog = ", indexInLog, "\n"); |
| if (indexInLog > logCursorIndex) { |
| if (verbose) |
| dataLog(" Bailing.\n"); |
| return false; |
| } |
| |
| unsigned oldIndexInLog = indexInLog; |
| |
| while (indexInLog--) { |
| Packet packet = m_log[indexInLog]; |
| |
| // If all callees opt into ShadowChicken, then this search will rapidly terminate when |
| // we find our frame. But if our frame's callee didn't emit a prologue packet because it |
| // didn't opt in, then we will keep looking backwards until we *might* find a different |
| // frame. If we've been given the callee and callerFrame as a filter, then it's unlikely |
| // that we will hit the wrong frame. But we don't always have that information. |
| // |
| // This means it's worth adding other filters. For example, we could track changes in |
| // stack size. Once we've seen a frame at some height, we're no longer interested in |
| // frames below that height. Also, we can break as soon as we see a frame higher than |
| // the one we're looking for. |
| // FIXME: Add more filters. |
| // https://bugs.webkit.org/show_bug.cgi?id=155685 |
| |
| if (packet.isPrologue() && packet.frame == frame |
| && (!callee || packet.callee == callee) |
| && (!callerFrame || packet.callerFrame == callerFrame)) { |
| if (verbose) |
| dataLog(" Found at indexInLog = ", indexInLog, "\n"); |
| return true; |
| } |
| } |
| |
| // This is an interesting eventuality. We will see this if ShadowChicken was not |
| // consistently enabled. We have a choice between: |
| // |
| // - Leaving the log index at -1, which will prevent the log from being considered. This is |
| // the most conservative. It means that we will not be able to recover tail-deleted frames |
| // from anything that sits above a frame that didn't log a prologue packet. This means |
| // that everyone who creates prologues must log prologue packets. |
| // |
| // - Restoring the log index to what it was before. This prevents us from considering |
| // whether this frame has tail-deleted frames behind it, but that's about it. The problem |
| // with this approach is that it might recover tail-deleted frames that aren't relevant. |
| // I haven't thought about this too deeply, though. |
| // |
| // It seems like the latter option is less harmful, so that's what we do. |
| indexInLog = oldIndexInLog; |
| |
| if (verbose) |
| dataLog(" Didn't find it.\n"); |
| return false; |
| }; |
| |
| Vector<Frame> toPush; |
| StackVisitor::visit( |
| exec, [&] (StackVisitor& visitor) -> StackVisitor::Status { |
| if (visitor->isInlinedFrame()) { |
| // FIXME: Handle inlining. |
| // https://bugs.webkit.org/show_bug.cgi?id=155686 |
| return StackVisitor::Continue; |
| } |
| CallFrame* callFrame = visitor->callFrame(); |
| if (verbose) |
| dataLog(" Examining ", RawPointer(callFrame), "\n"); |
| if (!toPush.isEmpty() && indexInLog < logCursorIndex |
| // This condition protects us from the case where advanceIndexInLogTo didn't find |
| // anything. |
| && m_log[indexInLog].frame == toPush.last().frame) { |
| if (verbose) |
| dataLog(" Going to loop through things with indexInLog = ", indexInLog, " and push-stack top = ", toPush.last(), "\n"); |
| for (;;) { |
| ASSERT(m_log[indexInLog].frame == toPush.last().frame); |
| |
| // Right now the index is pointing at a prologue packet of the last frame that |
| // we pushed. Peek behind that packet to see if there is a tail packet. If there |
| // is one then we know that there is a corresponding prologue packet that will |
| // tell us about a tail-deleted frame. |
| |
| if (!indexInLog) |
| break; |
| Packet lastPacket = m_log[indexInLog - 1]; |
| if (!lastPacket.isTail()) { |
| // Last frame that we recorded was not the outcome of a tail call. So, there |
| // will not be any more deleted frames. |
| // FIXME: We might want to have a filter here. Consider that this was a tail |
| // marker for a tail call to something that didn't log anything. It should |
| // be sufficient to give the tail marker a copy of the caller frame. |
| // https://bugs.webkit.org/show_bug.cgi?id=155687 |
| break; |
| } |
| indexInLog--; // Skip over the tail packet. |
| |
| if (!advanceIndexInLogTo(lastPacket.frame, nullptr, nullptr)) { |
| // We were unable to locate the prologue packet for this tail packet. That's |
| // quite suspect, so give up. |
| break; |
| } |
| Packet packet = m_log[indexInLog]; |
| bool isTailDeleted = true; |
| toPush.append(Frame(packet.callee, packet.frame, isTailDeleted)); |
| } |
| } |
| if (callFrame == highestPointSinceLastTime) { |
| if (verbose) |
| dataLog(" Bailing at ", RawPointer(callFrame), " because it's the highest point since last time.\n"); |
| return StackVisitor::Done; |
| } |
| advanceIndexInLogTo(callFrame, callFrame->callee(), callFrame->callerFrame()); |
| bool isTailDeleted = false; |
| toPush.append(Frame(visitor->callee(), callFrame, isTailDeleted)); |
| return StackVisitor::Continue; |
| }); |
| |
| if (verbose) |
| dataLog(" Pushing: ", listDump(toPush), "\n"); |
| |
| for (unsigned i = toPush.size(); i--;) |
| m_stack.append(toPush[i]); |
| |
| // We want to reset the log. There is a fun corner-case: there could be a tail marker at the end |
| // of this log. We could make that work by setting isTailDeleted on the top of stack, but that |
| // would require more corner cases in the complicated reconciliation code above. That code |
| // already knows how to handle a tail packet at the beginning, so we just leverage that here. |
| if (logCursorIndex && m_log[logCursorIndex - 1].isTail()) { |
| m_log[0] = m_log[logCursorIndex - 1]; |
| m_logCursor = m_log + 1; |
| } else |
| m_logCursor = m_log; |
| |
| if (verbose) |
| dataLog(" After pushing: ", *this, "\n"); |
| |
| // Remove tail frames until the stack is small enough again. |
| const unsigned stackSizeLimit = Options::shadowChickenStackSizeLimit(); |
| if (m_stack.size() > stackSizeLimit) { |
| unsigned dstIndex = 0; |
| unsigned srcIndex = 0; |
| unsigned size = m_stack.size(); |
| while (srcIndex < m_stack.size()) { |
| Frame frame = m_stack[srcIndex++]; |
| if (size > stackSizeLimit && frame.isTailDeleted) { |
| size--; |
| continue; |
| } |
| m_stack[dstIndex++] = frame; |
| } |
| RELEASE_ASSERT(dstIndex == size); |
| m_stack.resize(size); |
| } |
| |
| if (verbose) |
| dataLog(" After clean-up: ", *this, "\n"); |
| } |
| |
| void ShadowChicken::visitChildren(SlotVisitor& visitor) |
| { |
| for (unsigned i = m_logCursor - m_log; i--;) |
| visitor.appendUnbarrieredReadOnlyPointer(m_log[i].callee); |
| |
| for (Frame& frame : m_stack) |
| visitor.appendUnbarrieredReadOnlyPointer(frame.callee); |
| } |
| |
| void ShadowChicken::reset() |
| { |
| m_logCursor = m_log; |
| m_stack.clear(); |
| } |
| |
| void ShadowChicken::dump(PrintStream& out) const |
| { |
| out.print("{stack = [", listDump(m_stack), "], log = ["); |
| |
| CommaPrinter comma; |
| unsigned limit = static_cast<unsigned>(m_logCursor - m_log); |
| for (unsigned i = 0; i < limit; ++i) |
| out.print(comma, m_log[i]); |
| out.print("]}"); |
| } |
| |
| JSArray* ShadowChicken::functionsOnStack(ExecState* exec) |
| { |
| JSArray* result = constructEmptyArray(exec, 0); |
| |
| iterate( |
| exec->vm(), exec, |
| [&] (const Frame& frame) -> bool { |
| result->push(exec, frame.callee); |
| return true; |
| }); |
| |
| return result; |
| } |
| |
| } // namespace JSC |
| |
