# git rev-parse -q --verify 8cb55a3daebd4b38330b706117e1c8203ffaf3f5^{commit}
8cb55a3daebd4b38330b706117e1c8203ffaf3f5
already have revision, skipping fetch
# git checkout -q -f -B kisskb 8cb55a3daebd4b38330b706117e1c8203ffaf3f5
# git clean -qxdf
# < git log -1
# commit 8cb55a3daebd4b38330b706117e1c8203ffaf3f5
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Fri Feb 7 22:15:46 2020 +1100
# 
#     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 1d8f739b07bd ("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: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection")
#     Cc: stable@vger.kernel.org # v5.2+
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20200207122145.11928-1-mpe@ellerman.id.au
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 8cb55a3daebd4b38330b706117e1c8203ffaf3f5
# < make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pasemi_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  pasemi_defconfig
# make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-fixes_pasemi_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_pasemi_defconfig_powerpc-gcc5
# Build took: 0:01:36.485513