Dynamic memory managers are a crucial component of almost every modern software system. In addition to implementing efficient allocation and reclamation, memory managers provide the essential abstraction of memory as distinct objects, which underpins the properties of memory safety and type safety. Bugs in memory managers, while not common, are extremely hard to diagnose and fix. One reason is that their implementations often involve tricky pointer calculations, raw memory manipulation, and complex memory state invariants. While these properties are often documented, they are not specified in any precise, machine-checkable form. A second reason is that memory manager bugs can break the client application in bizarre ways that do not immediately implicate the memory manager at all. A third reason is that existing tools for debugging memory errors, such as Memcheck, cannot help because they rely on correct allocation and deallocation information to work. In this paper we present Permchecker, a tool designed specifically to detect and diagnose bugs in memory managers. The key idea in Permchecker is to make the expected structure of the heap explicit by associating typestates with each piece of memory. Typestate captures elements of both type (e.g., page, block, or cell) and state (e.g., allocated, free, or forwarded). Memory manager developers annotate their implementation with information about the expected typestates of memory and how heap operations change those typestates. At runtime, our system tracks the typestates and ensures that each memory access is consistent with the expected typestates. This technique detects errors quickly, before they corrupt the application or the memory manager itself, and it often provides accurate information about the reason for the error. The implementation of Permchecker uses a combination of compile-time annotation and instrumentation, and dynamic binary instrumentation (DBI). Because the overhead of DBI is fairly high, Permchecker is suitable for a testing and debugging setting and not for deployment. It works on a wide variety of existing systems, including explicit malloc/free memory managers and garbage collectors, such as those found in JikesRVM and OpenJDK. Since bugs in these systems are not numerous, we developed a testing methodology in which we automatically inject bugs into the code using bug patterns derived from real bugs. This technique allows us to test Permchecker on hundreds or thousands of buggy variants of the code. We find that Permchecker effectively detects and localizes errors in the vast majority of cases; without it, these bugs result in strange, incorrect behaviors usually long after the actual error occurs.
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CHEx86: Context-Sensitive Enforcement of Memory Safety via Microcode-Enabled Capabilities
This work introduces the CHEx86 processor architecture for securing applications, including legacy binaries, against a wide array of security exploits that target temporal and spatial memory safety vulnerabilities such as out-of-bounds accesses, use-after-free, double-free, and uninitialized reads, by instrumenting the code at the microcode-level, completely under-the-hood, with only limited access to source-level symbol information. In addition, this work presents a novel scheme for speculatively tracking pointer arithmetic and pointer movement, including the detection of pointer aliases in memory, at the machine code-level using a configurable set of automatically constructed rules. This architecture outperforms the address sanitizer, a state-of-the-art software-based mitigation by 59%, while eliminating porting, deployment, and verification costs that are invariably associated with recompilation.
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- Award ID(s):
- 1912608
- NSF-PAR ID:
- 10201445
- Date Published:
- Journal Name:
- 2020 ACM/IEEE 47th Annual International Symposium on Computer Architecture (ISCA)
- Page Range / eLocation ID:
- 762 to 775
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Use-after-free (UAF) vulnerabilities, in which dangling pointers remain after memory is released, remain a persistent problem for applications written in C and C++. In order to protect legacy code, prior work has attempted to track pointer propagation and invalidate dangling pointers at deallocation time, but this work has gaps in coverage, as it lacks support for tracking program variables promoted to CPU registers. Moreover, we find that these gaps can significantly hamper detection of UAF bugs: in a preliminary study with OSS-Fuzz, we found that more than half of the UAFs in real-world programs we examined (10/19) could not be detected by prior systems due to register promotion. In this paper, we introduce HeapExpo, a new system that fills this gap in coverage by parsimoniously identifying potential dangling pointer variables that may be lifted into registers by the compiler and marking them as volatile. In our experiments, we find that HeapExpo effectively detects UAFs missed by other systems with an overhead of 35% on the majority of SPEC CPU2006 and 66% when including two benchmarks that have high amounts of pointer propagation.more » « less
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Garbage collection (GC) support for unmanaged languages can reduce programming burden in reasoning about liveness of dynamic objects. It also avoids temporal memory safety violations and memory leaks.
Sound GC for weakly-typed languages such as C/C++, however, remains an unsolved problem. Current value-based GC solutions examine values of memory locations to discover the pointers, and the objects they point to. The approach is inherently unsound in the presence of arbitrary type casts and pointer manipulations, which are legal in C/C++. Such language features are regularly used, especially in low-level systems code.In this paper, we propose Dynamic Pointer Provenance Tracking to realize sound GC. We observe that pointers cannot be created out-of-thin-air, and they must have provenance to at least one valid allocation. Therefore, by tracking pointer provenance from the source (e.g., malloc) through both explicit data-flow and implicit control-flow, our GC has sound and precise information to compute the set of all reachable objects at any program state. We discuss several static analysis optimizations, that can be employed during compilation aided with profiling, to significantly reduce the overhead of dynamic provenance tracking from nearly 8× to 16% for well-behaved programs that adhere to the C standards. Pointer provenance based sound GC invocation is also 13% faster and reclaims 6% more memory on average, compared to an unsound value-based GC.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/ISCA45697.2020.00068
