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d99a015343
Authored by: Chris Williamson <chris.williamson@delphix.com> Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: John Kennedy <john.kennedy@delphix.com> Reviewed by: Dan Kimmel <dan.kimmel@delphix.com> Approved by: Garrett D'Amore <garrett@damore.org> Ported-by: Don Brady <don.brady@delphix.com> Ported-by: John Kennedy <john.kennedy@delphix.com> OpenZFS-issue: https://www.illumos.org/issues/7431 OpenZFS-commit: https://github.com/openzfs/openzfs/commit/dfc11533 Porting Notes: * The CLI long option arguments for '-t' and '-m' don't parse on linux * Switched from kmem_alloc to vmem_alloc in zcp_lua_alloc * Lua implementation is built as its own module (zlua.ko) * Lua headers consumed directly by zfs code moved to 'include/sys/lua/' * There is no native setjmp/longjump available in stock Linux kernel. Brought over implementations from illumos and FreeBSD * The get_temporary_prop() was adapted due to VFS platform differences * Use of inline functions in lua parser to reduce stack usage per C call * Skip some ZFS Test Suite ZCP tests on sparc64 to avoid stack overflow
81 lines
3.4 KiB
Plaintext
81 lines
3.4 KiB
Plaintext
#
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# CDDL HEADER START
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#
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# This file and its contents are supplied under the terms of the
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# Common Development and Distribution License ("CDDL"), version 1.0.
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# You may only use this file in accordance with the terms of version
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# 1.0 of the CDDL.
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#
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# A full copy of the text of the CDDL should have accompanied this
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# source. A copy of the CDDL is also available via the Internet at
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# http://www.illumos.org/license/CDDL.
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#
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# CDDL HEADER END
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#
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#
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# Copyright (c) 2017 by Delphix. All rights reserved.
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#
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Introduction
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------------
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This README describes the Lua interpreter source code that lives in the ZFS
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source tree to enable execution of ZFS channel programs, including its
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maintenance policy, the modifications that have been made to it, and how it
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should (and should not) be used.
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For a description of the Lua language and features exposed by ZFS channel
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programs, please refer to the zfs-program(1m) man page instead.
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Maintenance policy
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------------------
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The Lua runtime is considered stable software. Channel programs don't need much
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complicated logic, so updates to the Lua runtime from upstream are viewed as
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nice-to-have, but not required for channel programs to be well-supported. As
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such, the Lua runtime in ZFS should be updated on an as-needed basis for
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security vulnerabilities, but not much else.
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Modifications to Lua
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--------------------
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The version of the Lua runtime we're using in ZFS has been modified in a variety
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of ways to make it more useful for the specific purpose of running channel
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programs. These changes include:
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1. "Normal" Lua uses floating point for all numbers it stores, but those aren't
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useful inside ZFS / the kernel. We have changed the runtime to use int64_t
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throughout for all numbers.
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2. Some of the Lua standard libraries do file I/O or spawn processes, but
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neither of these make sense from inside channel programs. We have removed
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those libraries rather than reimplementing them using kernel APIs.
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3. The "normal" Lua runtime handles errors by failing fatally, but since this
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version of Lua runs inside the kernel we must handle these failures and
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return meaningful error codes to userland. We have customized the Lua
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failure paths so that they aren't fatal.
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4. Running poorly-vetted code inside the kernel is always a risk; even if the
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ability to do so is restricted to the root user, it's still possible to write
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an incorrect program that results in an infinite loop or massive memory use.
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We've added new protections into the Lua interpreter to limit the runtime
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(measured in number of Lua instructions run) and memory overhead of running
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a channel program.
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5. The Lua bytecode is not designed to be secure / safe, so it would be easy to
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pass invalid bytecode which can panic the kernel. By comparison, the parser
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is hardened and fails gracefully on invalid input. Therefore, we only accept
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Lua source code at the ioctl level and then interpret it inside the kernel.
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Each of these modifications have been tested in the zfs-test suite. If / when
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new modifications are made, new tests should be added to the suite located in
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zfs-tests/tests/functional/channel_program/lua_core.
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How to use this Lua interpreter
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-------------------------------
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From the above, it should be clear that this is not a general-purpose Lua
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interpreter. Additional work would be required to extricate this custom version
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of Lua from ZFS and make it usable by other areas of the kernel.
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