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Michael Ellerman 9dc086f1e9 powerpc/futex: Fix incorrect user access blocking 
The early versions of our kernel user access prevention (KUAP) were
written by Russell and Christophe, and didn't have separate
read/write access.

At some point I picked up the series and added the read/write access,
but I failed to update the usages in futex.h to correctly allow read
and write.

However we didn't notice because of another bug which was causing the
low-level code to always enable read and write. That bug was fixed
recently in commit 1d8f739b07 ("powerpc/kuap: Fix set direction in
allow/prevent_user_access()").

futex_atomic_cmpxchg_inatomic() is passed the user address as %3 and
does:

  1:     lwarx   %1,  0, %3
         cmpw    0,  %1, %4
         bne-    3f
  2:     stwcx.  %5,  0, %3

Which clearly loads and stores from/to %3. The logic in
arch_futex_atomic_op_inuser() is similar, so fix both of them to use
allow_read_write_user().

Without this fix, and with PPC_KUAP_DEBUG=y, we see eg:

  Bug: Read fault blocked by AMR!
  WARNING: CPU: 94 PID: 149215 at arch/powerpc/include/asm/book3s/64/kup-radix.h:126 __do_page_fault+0x600/0xf30
  CPU: 94 PID: 149215 Comm: futex_requeue_p Tainted: G        W         5.5.0-rc7-gcc9x-g4c25df5640ae #1
  ...
  NIP [c000000000070680] __do_page_fault+0x600/0xf30
  LR [c00000000007067c] __do_page_fault+0x5fc/0xf30
  Call Trace:
  [c00020138e5637e0] [c00000000007067c] __do_page_fault+0x5fc/0xf30 (unreliable)
  [c00020138e5638c0] [c00000000000ada8] handle_page_fault+0x10/0x30
  --- interrupt: 301 at cmpxchg_futex_value_locked+0x68/0xd0
      LR = futex_lock_pi_atomic+0xe0/0x1f0
  [c00020138e563bc0] [c000000000217b50] futex_lock_pi_atomic+0x80/0x1f0 (unreliable)
  [c00020138e563c30] [c00000000021b668] futex_requeue+0x438/0xb60
  [c00020138e563d60] [c00000000021c6cc] do_futex+0x1ec/0x2b0
  [c00020138e563d90] [c00000000021c8b8] sys_futex+0x128/0x200
  [c00020138e563e20] [c00000000000b7ac] system_call+0x5c/0x68

Fixes: de78a9c42a ("powerpc: Add a framework for Kernel Userspace Access Protection")
Cc: stable@vger.kernel.org # v5.2+
Reported-by: syzbot+e808452bad7c375cbee6@syzkaller-ppc64.appspotmail.com
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Link: https://lore.kernel.org/r/20200207122145.11928-1-mpe@ellerman.id.au
2020-02-08 21:48:39 +11:00
arch powerpc/futex: Fix incorrect user access blocking 2020-02-08 21:48:39 +11:00
block SCSI misc on 20200129 2020-01-29 18:16:16 -08:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto treewide: remove redundant IS_ERR() before error code check 2020-02-04 03:05:27 +00:00
Documentation powerpc updates for 5.6 2020-02-04 13:06:46 +00:00
drivers powerpc updates for 5.6 2020-02-04 13:06:46 +00:00
fs overlayfs update for 5.6 2020-02-04 11:45:21 +00:00
include Microblaze patches for 5.6-rc1 2020-02-04 11:58:07 +00:00
init init/main.c: fix misleading "This architecture does not have kernel memory protection" message 2020-01-31 10:30:41 -08:00
ipc proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
kernel proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
lib lib: new testcases for bitmap_parse{_user} 2020-02-04 03:05:27 +00:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Merge branch 'akpm' (patches from Andrew) 2020-02-04 07:24:48 +00:00
net treewide: remove redundant IS_ERR() before error code check 2020-02-04 03:05:27 +00:00
samples proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
scripts mm: remove __krealloc 2020-02-04 03:05:24 +00:00
security linux-kselftest-5.6-rc1-kunit 2020-01-29 15:25:34 -08:00
sound treewide: remove redundant IS_ERR() before error code check 2020-02-04 03:05:27 +00:00
tools powerpc updates for 5.6 2020-02-04 13:06:46 +00:00
usr initramfs: do not show compression mode choice if INITRAMFS_SOURCE is empty 2020-02-03 17:31:43 +00:00
virt Merge branch 'cve-2019-3016' into kvm-next-5.6 2020-01-30 18:47:59 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap RTC for 5.6 2020-02-04 07:03:40 +00:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS open: introduce openat2(2) syscall 2020-01-18 09:19:18 -05:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS hwspinlock updates for v5.6 2020-02-04 09:04:37 +00:00
Makefile Kbuild updates for v5.6 2020-02-01 10:01:52 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.