enable userspace port I/O for hypercalls in guest - #32
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Use ioperm() to explicitly allow port I/O to the port used for Nyx hypercalls. With this, the host kernel no longer needs to enable enable_vmware_backdoor=y. Benefits: - It avoids needing to change system-wide host configuration. - It lets KVM avoid intercepting guest #GP and decoding every instruction that hits #GP. Downsides: - Some stuff in the guest kernel will hit slowpaths; in particular, the syscall return path will probably run a few instructions more (tss_update_io_bitmap()). Switching between multiple tasks with separately-created ioperm() bitmasks would probably be slow because we'd hit the memcpy() in tss_copy_io_bitmap(), but as long as we just set up a single ioperm() bitmask in init, that shouldn't happen.
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Use
ioperm()to explicitly allow port I/O to the port used for Nyx hypercalls. With this, the host kernel no longer needs to enableenable_vmware_backdoor=y.Benefits:
Downsides:
tss_update_io_bitmap()).Switching between multiple tasks with separately-created
ioperm()bitmasks would probably be slow because we'd hit thememcpy()intss_copy_io_bitmap(), but as long as we just set up a singleioperm()bitmask in init, that shouldn't happen.With this patch applied, I can use
afl-fuzzin Nyx mode without enablingenable_vmware_backdoor.