Speakers
Description
Control-Flow Integrity (CFI) is a technique used to ensure that indirect
branches are not diverted from a pre-defined set of valid targets,
ensuring, for example, that a function pointer overwritten by an
exploited memory corruption bug is used to arbitrarily redirect the
control-flow of the program. The simpler way to achieve CFI is through
instrumenting the binary code being executed with proper checks that
verify the sanity of the indirect branches whenever they happen. To help
with this goal, some CPU vendors enhanced their hardware with extensions
that make these checks simpler and faster. Currently there are 4
different instrumentation setups being more broadly discussed for
upstream: kCFI, which is a full software instrumentation that employs a
fine-grained policy to validate indirect branch targets; ARM's BTI,
which is an ARM hardware extension that achieves CFI in a
coarse-grained, more relaxed form; Intel's IBT, which is an X86 hardware
extension that similarly to BTI also achieves coarse-grained CFI, but
with the benefit of also enforcing this over speculative paths; and
FineIBT, which is a software/hardware hybrid technique which combines
Intel's IBT with software instrumentation to make it fine-grained
without losing its good performance while still adding resiliency
against speculative attacks.
In this session, kernel developers and researchers (Sami Tolvanen, Mark
Rutland, Peter Zijlstra, Joao Moreira) will provide an overview on the
different implementations, their upstream enablement and discuss the
contrast in approaches such as granularity or implications of design
differences such as callee/caller-side checks.
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