# git rev-parse -q --verify 51d92826594c3ac1f9b7179a3ab246394a11ecd8^{commit}
# git fetch -q -n -f git://gitlab.ozlabs.ibm.com/linuxppc/linux.git fixes-test
warning: The last gc run reported the following. Please correct the root cause
and remove .git/gc.log.
Automatic cleanup will not be performed until the file is removed.

warning: There are too many unreachable loose objects; run 'git prune' to remove them.

# git rev-parse -q --verify 51d92826594c3ac1f9b7179a3ab246394a11ecd8^{commit}
51d92826594c3ac1f9b7179a3ab246394a11ecd8
# git checkout -q -f -B kisskb 51d92826594c3ac1f9b7179a3ab246394a11ecd8
# git clean -qxdf
# < git log -1
# commit 51d92826594c3ac1f9b7179a3ab246394a11ecd8
# Author: Christophe Leroy <christophe.leroy@csgroup.eu>
# Date:   Mon Feb 1 06:29:50 2021 +0000
# 
#     powerpc/603: Fix protection of user pages mapped with PROT_NONE
#     
#     On book3s/32, page protection is defined by the PP bits in the PTE
#     which provide the following protection depending on the access
#     keys defined in the matching segment register:
#     - PP 00 means RW with key 0 and N/A with key 1.
#     - PP 01 means RW with key 0 and RO with key 1.
#     - PP 10 means RW with both key 0 and key 1.
#     - PP 11 means RO with both key 0 and key 1.
#     
#     Since the implementation of kernel userspace access protection,
#     PP bits have been set as follows:
#     - PP00 for pages without _PAGE_USER
#     - PP01 for pages with _PAGE_USER and _PAGE_RW
#     - PP11 for pages with _PAGE_USER and without _PAGE_RW
#     
#     For kernelspace segments, kernel accesses are performed with key 0
#     and user accesses are performed with key 1. As PP00 is used for
#     non _PAGE_USER pages, user can't access kernel pages not flagged
#     _PAGE_USER while kernel can.
#     
#     For userspace segments, both kernel and user accesses are performed
#     with key 0, therefore pages not flagged _PAGE_USER are still
#     accessible to the user.
#     
#     This shouldn't be an issue, because userspace is expected to be
#     accessible to the user. But unlike most other architectures, powerpc
#     implements PROT_NONE protection by removing _PAGE_USER flag instead of
#     flagging the page as not valid. This means that pages in userspace
#     that are not flagged _PAGE_USER shall remain inaccessible.
#     
#     To get the expected behaviour, just mimic other architectures in the
#     TLB miss handler by checking _PAGE_USER permission on userspace
#     accesses as if it was the _PAGE_PRESENT bit.
#     
#     Note that this problem only is only for 603 cores. The 604+ have
#     an hash table, and hash_page() function already implement the
#     verification of _PAGE_USER permission on userspace pages.
#     
#     Fixes: f342adca3afc ("powerpc/32s: Prepare Kernel Userspace Access Protection")
#     Cc: stable@vger.kernel.org # v5.2+
#     Reported-by: Christoph Plattner <christoph.plattner@thalesgroup.com>
#     Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/4a0c6e3bb8f0c162457bf54d9bc6fd8d7b55129f.1612160907.git.christophe.leroy@csgroup.eu
# < /opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-gcc --version
# < /opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-ld --version
# < git log --format=%s --max-count=1 51d92826594c3ac1f9b7179a3ab246394a11ecd8
# < make -s -j 120 ARCH=arm64 O=/kisskb/build/powerpc-fixes_arm64-defconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-  defconfig
# < make -s -j 120 ARCH=arm64 O=/kisskb/build/powerpc-fixes_arm64-defconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-  help
# make -s -j 120 ARCH=arm64 O=/kisskb/build/powerpc-fixes_arm64-defconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-  olddefconfig
# make -s -j 120 ARCH=arm64 O=/kisskb/build/powerpc-fixes_arm64-defconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-  
arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum
arch/arm64/Makefile:33: LSE atomics not supported by binutils
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_arm64-defconfig_arm64-gcc5.4
# Build took: 0:04:03.666688