# 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 # 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 # 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 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux- mpc885_ads_defconfig # Added to kconfig CONFIG_HUGETLBFS=y # yes \n | make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux- oldconfig yes: standard output: Broken pipe # make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux- Image Name: Linux-5.5.0-g8cb55a3daebd Created: Sat Feb 8 01:13:24 2020 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 1958620 Bytes = 1912.71 KiB = 1.87 MiB Load Address: 00400000 Entry Point: 00400204 Completed OK # rm -rf /kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc5 # Build took: 0:00:51.179912