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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Paul Burton f8fffebdea
MIPS: BPF: Disable MIPS32 eBPF JIT 
Commit 716850ab10 ("MIPS: eBPF: Initial eBPF support for MIPS32
architecture.") enabled our eBPF JIT for MIPS32 kernels, whereas it has
previously only been availailable for MIPS64. It was my understanding at
the time that the BPF test suite was passing & JITing a comparable
number of tests to our cBPF JIT [1], but it turns out that was not the
case.

The eBPF JIT has a number of problems on MIPS32:

- Most notably various code paths still result in emission of MIPS64
  instructions which will cause reserved instruction exceptions & kernel
  panics when run on MIPS32 CPUs.

- The eBPF JIT doesn't account for differences between the O32 ABI used
  by MIPS32 kernels versus the N64 ABI used by MIPS64 kernels. Notably
  arguments beyond the first 4 are passed on the stack in O32, and this
  is entirely unhandled when JITing a BPF_CALL instruction. Stack space
  must be reserved for arguments even if they all fit in registers, and
  the callee is free to assume that stack space has been reserved for
  its use - with the eBPF JIT this is not the case, so calling any
  function can result in clobbering values on the stack & unpredictable
  behaviour. Function arguments in eBPF are always 64-bit values which
  is also entirely unhandled - the JIT still uses a single (32-bit)
  register per argument. As a result all function arguments are always
  passed incorrectly when JITing a BPF_CALL instruction, leading to
  kernel crashes or strange behavior.

- The JIT attempts to bail our on use of ALU64 instructions or 64-bit
  memory access instructions. The code doing this at the start of
  build_one_insn() incorrectly checks whether BPF_OP() equals BPF_DW,
  when it should really be checking BPF_SIZE() & only doing so when
  BPF_CLASS() is one of BPF_{LD,LDX,ST,STX}. This results in false
  positives that cause more bailouts than intended, and that in turns
  hides some of the problems described above.

- The kernel's cBPF->eBPF translation makes heavy use of 64-bit eBPF
  instructions that the MIPS32 eBPF JIT bails out on, leading to most
  cBPF programs not being JITed at all.

Until these problems are resolved, revert the enabling of the eBPF JIT
on MIPS32 done by commit 716850ab10 ("MIPS: eBPF: Initial eBPF support
for MIPS32 architecture.").

Note that this does not undo the changes made to the eBPF JIT by that
commit, since they are a useful starting point to providing MIPS32
support - they're just not nearly complete.

[1] https://lore.kernel.org/linux-mips/MWHPR2201MB13583388481F01A422CE7D66D4410@MWHPR2201MB1358.namprd22.prod.outlook.com/

Signed-off-by: Paul Burton <paulburton@kernel.org>
Fixes: 716850ab10 ("MIPS: eBPF: Initial eBPF support for MIPS32 architecture.")
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Hassan Naveed <hnaveed@wavecomp.com>
Cc: Tony Ambardar <itugrok@yahoo.com>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: <stable@vger.kernel.org> # v5.2+
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
 		2019-12-18 15:15:03 -08:00
Documentation A few MIPS fixes: 2019-11-01 14:36:44 -07:00
LICENSES
…
arch MIPS: BPF: Disable MIPS32 eBPF JIT 2019-12-18 15:15:03 -08:00
block blk-wbt: fix performance regression in wbt scale_up/scale_down 2019-10-06 09:26:41 -06:00
certs
…
crypto Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
drivers MIPS: Kconfig: Use correct form for 'depends on' 2019-12-02 10:51:01 -08:00
fs A few tracing fixes: 2019-10-13 14:47:10 -07:00
include A few MIPS fixes: 2019-11-01 14:36:44 -07:00
init Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel A few tracing fixes: 2019-10-13 14:47:10 -07:00
lib Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-10-12 14:46:14 -07:00
mm for-linus-20191010 2019-10-11 08:45:32 -07:00
net NFS Client Bugfixes for Linux 5.4-rc3 2019-10-11 14:28:59 -07:00
samples rpmsg updates for v5.4 2019-09-22 10:58:15 -07:00
scripts A few tracing fixes: 2019-10-13 14:47:10 -07:00
security selinux/stable-5.4 PR 20191007 2019-10-08 10:51:37 -07:00
sound sound fixes for 5.4-rc1 2019-09-24 16:46:16 -07:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-10-12 15:15:17 -07:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM/arm fixes for 5.4, take #1 2019-10-03 12:08:50 +02:00
.clang-format
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.cocciconfig
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.get_maintainer.ignore
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.gitattributes
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.gitignore
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.mailmap MAINTAINERS: Use @kernel.org address for Paul Burton 2019-10-18 14:27:19 -07:00
COPYING
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CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild
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Kconfig
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MAINTAINERS A few MIPS fixes: 2019-11-01 14:36:44 -07:00
Makefile Linux 5.4-rc3 2019-10-13 16:37:36 -07:00
README
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.