# git rev-parse -q --verify 457afdc0071dbd343a59426890b9677ca2882c23^{commit}
457afdc0071dbd343a59426890b9677ca2882c23
already have revision, skipping fetch
# git checkout -q -f -B kisskb 457afdc0071dbd343a59426890b9677ca2882c23
# git clean -qxdf
# < git log -1
# commit 457afdc0071dbd343a59426890b9677ca2882c23
# Author: Gustavo Romero <gromero@linux.ibm.com>
# Date:   Tue Sep 3 14:47:17 2019 +1000
# 
#     powerpc/tm: Fix restoring FP/VMX facility incorrectly on interrupts
#     
#     When in userspace and MSR FP=0 the hardware FP state is unrelated to
#     the current process. This is extended for transactions where if tbegin
#     is run with FP=0, the hardware checkpoint FP state will also be
#     unrelated to the current process. Due to this, we need to ensure this
#     hardware checkpoint is updated with the correct state before we enable
#     FP for this process.
#     
#     Unfortunately we get this wrong when returning to a process from a
#     hardware interrupt. A process that starts a transaction with FP=0 can
#     take an interrupt. When the kernel returns back to that process, we
#     change to FP=1 but with hardware checkpoint FP state not updated. If
#     this transaction is then rolled back, the FP registers now contain the
#     wrong state.
#     
#     The process looks like this:
#        Userspace:                      Kernel
#     
#                    Start userspace
#                     with MSR FP=0 TM=1
#                       < -----
#        ...
#        tbegin
#        bne
#                    Hardware interrupt
#                        ---- >
#                                         <do_IRQ...>
#                                         ....
#                                         ret_from_except
#                                           restore_math()
#                                             /* sees FP=0 */
#                                             restore_fp()
#                                               tm_active_with_fp()
#                                                 /* sees FP=1 (Incorrect) */
#                                               load_fp_state()
#                                             FP = 0 -> 1
#                       < -----
#                    Return to userspace
#                      with MSR TM=1 FP=1
#                      with junk in the FP TM checkpoint
#        TM rollback
#        reads FP junk
#     
#     When returning from the hardware exception, tm_active_with_fp() is
#     incorrectly making restore_fp() call load_fp_state() which is setting
#     FP=1.
#     
#     The fix is to remove tm_active_with_fp().
#     
#     tm_active_with_fp() is attempting to handle the case where FP state
#     has been changed inside a transaction. In this case the checkpointed
#     and transactional FP state is different and hence we must restore the
#     FP state (ie. we can't do lazy FP restore inside a transaction that's
#     used FP). It's safe to remove tm_active_with_fp() as this case is
#     handled by restore_tm_state(). restore_tm_state() detects if FP has
#     been using inside a transaction and will set load_fp and call
#     restore_math() to ensure the FP state (checkpoint and transaction) is
#     restored.
#     
#     This is a data integrity problem for the current process as the FP
#     registers are corrupted. It's also a security problem as the FP
#     registers from one process may be leaked to another.
#     
#     Similarly for VMX.
#     
#     A simple testcase to replicate this will be posted to
#     tools/testing/selftests/powerpc/tm/tm-poison.c
#     
#     This fixes CVE-2019-15031.
#     
#     Fixes: a7771176b439 ("powerpc: Don't enable FP/Altivec if not checkpointed")
#     Cc: stable@vger.kernel.org # 4.15+
#     Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
#     Signed-off-by: Michael Neuling <mikey@neuling.org>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20190903044718.13773-2-mikey@neuling.org
# < /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 457afdc0071dbd343a59426890b9677ca2882c23
# < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_44x_iss476-smp_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  44x/iss476-smp_defconfig

WARNING: unmet direct dependencies detected for HOTPLUG_CPU
  Depends on [n]: SMP [=y] && (PPC_PSERIES [=n] || PPC_PMAC [=n] || PPC_POWERNV [=n] || FSL_SOC_BOOKE [=n])
  Selected by [y]:
  - PM_SLEEP_SMP [=y] && SMP [=y] && (ARCH_SUSPEND_POSSIBLE [=y] || ARCH_HIBERNATION_POSSIBLE [=y]) && PM_SLEEP [=y]

WARNING: unmet direct dependencies detected for HOTPLUG_CPU
  Depends on [n]: SMP [=y] && (PPC_PSERIES [=n] || PPC_PMAC [=n] || PPC_POWERNV [=n] || FSL_SOC_BOOKE [=n])
  Selected by [y]:
  - PM_SLEEP_SMP [=y] && SMP [=y] && (ARCH_SUSPEND_POSSIBLE [=y] || ARCH_HIBERNATION_POSSIBLE [=y]) && PM_SLEEP [=y]
# make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_44x_iss476-smp_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
INFO: Uncompressed kernel (size 0x615504) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x700000)
INFO: Uncompressed kernel (size 0x615504) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x700000)
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_44x_iss476-smp_defconfig_powerpc-gcc5
# Build took: 0:00:34.283160