# git rev-parse -q --verify 4da9f3302615f4191814f826054846bf843e24fa^{commit}
# git fetch -q -n -f git://fs.ozlabs.ibm.com/kernel/linus master
# git rev-parse -q --verify 4da9f3302615f4191814f826054846bf843e24fa^{commit}
4da9f3302615f4191814f826054846bf843e24fa
# git checkout -q -f -B kisskb 4da9f3302615f4191814f826054846bf843e24fa
# git clean -qxdf
# < git log -1
# commit 4da9f3302615f4191814f826054846bf843e24fa
# Merge: 125cfa0d4d14 d029bff60aa6
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Tue Aug 4 21:16:22 2020 -0700
# 
#     Merge tag 'x86-fsgsbase-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
#     
#     Pull x86 fsgsbase from Thomas Gleixner:
#      "Support for FSGSBASE. Almost 5 years after the first RFC to support
#       it, this has been brought into a shape which is maintainable and
#       actually works.
#     
#       This final version was done by Sasha Levin who took it up after Intel
#       dropped the ball. Sasha discovered that the SGX (sic!) offerings out
#       there ship rogue kernel modules enabling FSGSBASE behind the kernels
#       back which opens an instantanious unpriviledged root hole.
#     
#       The FSGSBASE instructions provide a considerable speedup of the
#       context switch path and enable user space to write GSBASE without
#       kernel interaction. This enablement requires careful handling of the
#       exception entries which go through the paranoid entry path as they
#       can no longer rely on the assumption that user GSBASE is positive (as
#       enforced via prctl() on non FSGSBASE enabled systemn).
#     
#       All other entries (syscalls, interrupts and exceptions) can still just
#       utilize SWAPGS unconditionally when the entry comes from user space.
#       Converting these entries to use FSGSBASE has no benefit as SWAPGS is
#       only marginally slower than WRGSBASE and locating and retrieving the
#       kernel GSBASE value is not a free operation either. The real benefit
#       of RD/WRGSBASE is the avoidance of the MSR reads and writes.
#     
#       The changes come with appropriate selftests and have held up in field
#       testing against the (sanitized) Graphene-SGX driver"
#     
#     * tag 'x86-fsgsbase-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
#       x86/fsgsbase: Fix Xen PV support
#       x86/ptrace: Fix 32-bit PTRACE_SETREGS vs fsbase and gsbase
#       selftests/x86/fsgsbase: Add a missing memory constraint
#       selftests/x86/fsgsbase: Fix a comment in the ptrace_write_gsbase test
#       selftests/x86: Add a syscall_arg_fault_64 test for negative GSBASE
#       selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE
#       selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write
#       Documentation/x86/64: Add documentation for GS/FS addressing mode
#       x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2
#       x86/cpu: Enable FSGSBASE on 64bit by default and add a chicken bit
#       x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit
#       x86/entry/64: Introduce the FIND_PERCPU_BASE macro
#       x86/entry/64: Switch CR3 before SWAPGS in paranoid entry
#       x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation
#       x86/process/64: Use FSGSBASE instructions on thread copy and ptrace
#       x86/process/64: Use FSBSBASE in switch_to() if available
#       x86/process/64: Make save_fsgs_for_kvm() ready for FSGSBASE
#       x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions
#       x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions
#       x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE
#       ...
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-ld --version
# < git log --format=%s --max-count=1 4da9f3302615f4191814f826054846bf843e24fa
# < make -s -j 24 ARCH=x86_64 O=/kisskb/build/linus-rand_x86_64-randconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  randconfig
KCONFIG_SEED=0x422609C3
# Added to kconfig CONFIG_STANDALONE=y
# Added to kconfig CONFIG_PREVENT_FIRMWARE_BUILD=y
# Added to kconfig CONFIG_CC_STACKPROTECTOR_STRONG=n
# Added to kconfig CONFIG_GCC_PLUGINS=n
# Added to kconfig CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=n
# Added to kconfig CONFIG_GCC_PLUGIN_SANCOV=n
# Added to kconfig CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n
# < make -s -j 24 ARCH=x86_64 O=/kisskb/build/linus-rand_x86_64-randconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  help
# make -s -j 24 ARCH=x86_64 O=/kisskb/build/linus-rand_x86_64-randconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  olddefconfig
.config:4738:warning: override: reassigning to symbol STANDALONE
.config:4739:warning: override: reassigning to symbol PREVENT_FIRMWARE_BUILD
# make -s -j 24 ARCH=x86_64 O=/kisskb/build/linus-rand_x86_64-randconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  
Completed OK
# rm -rf /kisskb/build/linus-rand_x86_64-randconfig_x86_64-gcc8
# Build took: 0:04:40.759877