Modern operating systems are monolithic. Today, however, lack of isolation is one of the main factors undermining security of the kernel. Inherent complexity of the kernel code and rapid development pace combined with the use of unsafe, low-level programming language results in a steady stream of errors. Even after decades of efforts to make commodity kernels more secure, i.e., development of numerous static and dynamic approaches aimed to prevent exploitation of most common errors, several hundreds of serious kernel vulnerabilities are reported every year. Unfortunately, in a monolithic kernel a single exploitable vulnerability potentially provides an attacker with access to the entire kernel.Modern kernels need isolation as a practical means of confining the effects of exploits to individual kernel subsystems. Historically, introducing isolation in the kernel is hard. First, commodity hardware interfaces provide no support for efficient, fine-grained isolation. Second, the complexity of a modern kernel prevents a naive decomposition effort. Our work on Lightweight Execution Domains (LXDs) takes a step towards enabling isolation in a full-featured operating system kernel. LXDs allow one to take an existing kernel subsystem and run it inside an isolated domain with minimal or no modifications and with a minimal overhead. We evaluate our approach by developing isolated versions of several performance-critical device drivers in the Linux kernel.
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Lightweight kernel isolation with virtualization and VM functions
Commodity operating systems execute core kernel subsystems
in a single address space along with hundreds of dynamically
loaded extensions and device drivers. Lack of isolation
within the kernel implies that a vulnerability in any of the
kernel subsystems or device drivers opens a way to mount a
successful attack on the entire kernel.
Historically, isolation within the kernel remained prohibitive
due to the high cost of hardware isolation primitives.
Recent CPUs, however, bring a new set of mechanisms. Extended
page-table (EPT) switching with VM functions and
memory protection keys (MPKs) provide memory isolation
and invocations across boundaries of protection domains
with overheads comparable to system calls. Unfortunately,
neither MPKs nor EPT switching provide architectural support
for isolation of privileged ring 0 kernel code, i.e., control
of privileged instructions and well-defined entry points to
securely restore state of the system on transition between
isolated domains.
Our work develops a collection of techniques for lightweight
isolation of privileged kernel code. To control execution
of privileged instructions, we rely on a minimal
hypervisor that transparently deprivileges the system into
a non-root VT-x guest. We develop a new isolation boundary
that leverages extended page table (EPT) switching with
the VMFUNC instruction. We define a set of invariants that
allows us to isolate kernel components in the face of an intricate
execution model of the kernel, e.g., provide isolation
of preemptable, concurrent interrupt handlers. To minimize
overheads of virtualization, we develop support for exitless
interrupt delivery across isolated domains. We evaluate our
approach by developing isolated versions of several device
drivers in the Linux kernel.
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- NSF-PAR ID:
- 10163948
- Date Published:
- Journal Name:
- 16th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments
- Page Range / eLocation ID:
- 157 to 171
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3381052.3381328
