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instruction count measures the symbolic-emulation workload per sample and |
serves as a proxy for the slice's complexity. The more instructions |
executed under symbolic semantics, the broader the data-flow fan-out |
across registers and memory. By normalizing mutation priorities against |
this metric, E0 favors inputs that exercise larger slices of |
data-dependent code, increasing the chance of uncovering vulnerabilities |
requiring complex arithmetic or multi-step memory manipulations. |
--------------------------------------------------------------------------- |
4 | Hash of Unique Emulated Instruction Addresses per Run |
--------------------------------------------------------------------------- |
To detect overlapping symbolic-emulation regions across samples, E0 |
maintains a running, order-insensitive hash over the set of all unique |
instruction (RVA) relative virtual addresses emulated under symbolic mode |
across all sessions, modules, and threads. Each time Triton symbolically |
processes an instruction, E0 inserts its address into a global hash |
accumulator. At the end of the run, this accumulator represents the |
"symbolic footprint" of that sample. Comparing hash values between runs |
reveals whether two samples touched the same set of data-dependent |
instructions (regardless of execution order or frequency). Distinct hashes |
indicate that a new sample has uncovered previously unexplored symbolic |
paths; identical hashes suggest redundant coverage. This high-resolution |
fingerprint far surpasses basic-block bitmaps by accounting for |
instruction-level context, multi-module interactions, and multi-threaded |
execution. |
--------------------------------------------------------------------------- |
5 | Unique SymDef ID Count per Run |
--------------------------------------------------------------------------- |
Each time E0 captures a symbolic definition (SymDef), it checks whether |
that SymDef ID has been seen in previous runs. If not, the SymDef is |
marked as unique for this sample. The total number of unique SymDef IDs |
captured in a run reflects the number of new function-boundary propagation |
points discovered during execution. A higher count indicates that symbolic |
input has reached new regions of code and crossed additional def-use |
boundaries, expanding the observed symbolic data-flow graph. This simple |
metric helps identify samples that extend input influence into unexplored |
functions or modules. |
--------------------------------------------------------------------------- |
Because these metrics span from broad-level (session count) to fine- |
grained (instruction-address hash), E0 combines them into a unified |
data-flow coverage score that prioritizes samples driving novel or deeper |
symbolic activity; those that spawn new emulation sessions, introduce |
additional symbolic definitions, exercise previously unseen emulated |
instructions, or previously unseen symdefs. By focusing on inputs that |
uncover fresh data-flow frontiers rather than merely toggling basic-block |
bits, E0 rapidly directs exploration toward code regions where untrusted |
input meaningfully influences computation. |
This data-flow orientation yields key benefits: precise tracking of how |
untrusted bytes propagate; reduced redundancy through instruction-level |
hashing and definition counts; and comprehensive cross-module, cross- |
thread coverage via a unified instruction-address footprint. In short, |
Data-Flow Coverage Guidance transforms low-level symbolic events into |
high-resolution signals, enabling E0 to probe untrusted data paths with |
surgical accuracy and accelerate the discovery of deep, semantically |
relevant vulnerabilities. |
--[ 9 - Fine-Grained Memory Instrumentation via Hardware Watchpoints |
Page-level guarding introduced severe performance penalties and didn't |
scale. To address this, E0 falls back on the CPU's built-in hardware |
watchpoints, which can monitor much smaller, power-of-two-aligned (address |
and size) regions within a page. Because each core only provides four |
debug registers, we employ a hierarchical bitmap and recursive splitting |
algorithm to efficiently carve a 16 KB page into at most four minimally |
sized watchpoint blocks, often using even fewer when possible. |
.------------------------------------------------------------------. |
| Hardware Watchpoint Constraints | |
| | |
| - Only four watchpoints per core | |
| - Each WP must cover a 2^N-byte region, aligned to its size | |
| - Any untracked byte in that region still fires an exception | |
| - Scattered inputs force oversized regions -> spurious traps. | |
'------------------------------------------------------------------' |
Tracking an arbitrary set of bytes inside a 16KB page requires carving |
that page into smaller power-of-two blocks. To do this efficiently, and |
within the constraint of only four hardware watchpoint slots, we use a |
three-level bitmap hierarchy and a recursive splitting strategy: |
rootBitmap -> pageSegments -> pageQwords |
[ Page (16KB) ] |
| |
.---v---. Level 1: 32 segments (512B each) |
| seg | rootBitmap -> 1...0...1...0... (1 bit per 512B segment) |
'-------' |
| |
.---v---. Level 2: 64 qwords per segment (8B each) |
| qword | pageSegments[n] -> 0x... (1 bit per 8B qword) |
'-------' |
| |
.---v---. Level 3: byte mask per qword |
| byte | pageQwords[i] -> 0b10110010 (1 bit per byte in the qword) |
'-------' |
1. Level 1 (root): A 32-bit root bitmap marks which 512B segments contain |
any tracked byte. |
2. Level 2 (segments): For each set bit, a 64-bit segment mask identifies |
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