# git rev-parse -q --verify 8e1278444446fc97778a5e5c99bca1ce0bbc5ec9^{commit}
8e1278444446fc97778a5e5c99bca1ce0bbc5ec9
already have revision, skipping fetch
# git checkout -q -f -B kisskb 8e1278444446fc97778a5e5c99bca1ce0bbc5ec9
# git clean -qxdf
# < git log -1
# commit 8e1278444446fc97778a5e5c99bca1ce0bbc5ec9
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Tue Jun 7 00:34:56 2022 +1000
# 
#     powerpc/32: Fix overread/overwrite of thread_struct via ptrace
#     
#     The ptrace PEEKUSR/POKEUSR (aka PEEKUSER/POKEUSER) API allows a process
#     to read/write registers of another process.
#     
#     To get/set a register, the API takes an index into an imaginary address
#     space called the "USER area", where the registers of the process are
#     laid out in some fashion.
#     
#     The kernel then maps that index to a particular register in its own data
#     structures and gets/sets the value.
#     
#     The API only allows a single machine-word to be read/written at a time.
#     So 4 bytes on 32-bit kernels and 8 bytes on 64-bit kernels.
#     
#     The way floating point registers (FPRs) are addressed is somewhat
#     complicated, because double precision float values are 64-bit even on
#     32-bit CPUs. That means on 32-bit kernels each FPR occupies two
#     word-sized locations in the USER area. On 64-bit kernels each FPR
#     occupies one word-sized location in the USER area.
#     
#     Internally the kernel stores the FPRs in an array of u64s, or if VSX is
#     enabled, an array of pairs of u64s where one half of each pair stores
#     the FPR. Which half of the pair stores the FPR depends on the kernel's
#     endianness.
#     
#     To handle the different layouts of the FPRs depending on VSX/no-VSX and
#     big/little endian, the TS_FPR() macro was introduced.
#     
#     Unfortunately the TS_FPR() macro does not take into account the fact
#     that the addressing of each FPR differs between 32-bit and 64-bit
#     kernels. It just takes the index into the "USER area" passed from
#     userspace and indexes into the fp_state.fpr array.
#     
#     On 32-bit there are 64 indexes that address FPRs, but only 32 entries in
#     the fp_state.fpr array, meaning the user can read/write 256 bytes past
#     the end of the array. Because the fp_state sits in the middle of the
#     thread_struct there are various fields than can be overwritten,
#     including some pointers. As such it may be exploitable.
#     
#     It has also been observed to cause systems to hang or otherwise
#     misbehave when using gdbserver, and is probably the root cause of this
#     report which could not be easily reproduced:
#       https://lore.kernel.org/linuxppc-dev/dc38afe9-6b78-f3f5-666b-986939e40fc6@keymile.com/
#     
#     Rather than trying to make the TS_FPR() macro even more complicated to
#     fix the bug, or add more macros, instead add a special-case for 32-bit
#     kernels. This is more obvious and hopefully avoids a similar bug
#     happening again in future.
#     
#     Note that because 32-bit kernels never have VSX enabled the code doesn't
#     need to consider TS_FPRWIDTH/OFFSET at all. Add a BUILD_BUG_ON() to
#     ensure that 32-bit && VSX is never enabled.
#     
#     Fixes: 87fec0514f61 ("powerpc: PTRACE_PEEKUSR/PTRACE_POKEUSER of FPR registers in little endian builds")
#     Cc: stable@vger.kernel.org # v3.13+
#     Reported-by: Ariel Miculas <ariel.miculas@belden.com>
#     Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20220609133245.573565-1-mpe@ellerman.id.au
# < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-ld --version
# < git log --format=%s --max-count=1 8e1278444446fc97778a5e5c99bca1ce0bbc5ec9
# < make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-fixes_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-  defconfig
# Added to kconfig CONFIG_DEBUG_INFO_BTF=n
# Added to kconfig 
# < make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-fixes_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-  help
# make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-fixes_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-  olddefconfig
# make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-fixes_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/s390-linux/bin/s390-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_s390-defconfig_s390x-gcc8
# Build took: 0:02:00.468545