# git rev-parse -q --verify b86f6789c355a86ff6c3a8d5ab24774fd66a5a51^{commit}
# git fetch -q -n -f git://gitlab.ozlabs.ibm.com/linuxppc/linux.git next-test
# git rev-parse -q --verify b86f6789c355a86ff6c3a8d5ab24774fd66a5a51^{commit}
b86f6789c355a86ff6c3a8d5ab24774fd66a5a51
# git checkout -q -f -B kisskb b86f6789c355a86ff6c3a8d5ab24774fd66a5a51
# git clean -qxdf
# < git log -1
# commit b86f6789c355a86ff6c3a8d5ab24774fd66a5a51
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Mon Mar 16 23:44:21 2020 +1100
# 
#     powerpc/64: Prevent stack protection in early boot
#     
#     The previous commit reduced the amount of code that is run before we
#     setup a paca. However there are still a few remaining functions that
#     run with no paca, or worse, with an arbitrary value in r13 that will
#     be used as a paca pointer.
#     
#     In particular the stack protector canary is stored in the paca, so if
#     stack protector is activated for any of these functions we will read
#     the stack canary from wherever r13 points. If r13 happens to point
#     outside of memory we will get a machine check / checkstop.
#     
#     For example if we modify initialise_paca() to trigger stack
#     protection, and then boot in the mambo simulator with r13 poisoned in
#     skiboot before calling the kernel:
#     
#       DEBUG: 19952232: (19952232): INSTRUCTION: PC=0xC0000000191FC1E8: [0x3C4C006D]: addis   r2,r12,0x6D [fetch]
#       DEBUG: 19952236: (19952236): INSTRUCTION: PC=0xC00000001807EAD8: [0x7D8802A6]: mflr    r12 [fetch]
#       FATAL ERROR: 19952276: (19952276): Check Stop for 0:0: Machine Check with ME bit of MSR off
#       DEBUG: 19952276: (19952276): INSTRUCTION: PC=0xC0000000191FCA7C: [0xE90D0CF8]: ld      r8,0xCF8(r13) [Instruction Failed]
#       INFO: 19952276: (19952277): ** Execution stopped: Mambo Error, Machine Check Stop,  **
#       systemsim % bt
#       pc:                             0xC0000000191FCA7C      initialise_paca+0x54
#       lr:                             0xC0000000191FC22C      early_setup+0x44
#       stack:0x00000000198CBED0        0x0     +0x0
#       stack:0x00000000198CBF00        0xC0000000191FC22C      early_setup+0x44
#       stack:0x00000000198CBF90        0x1801C968      +0x1801C968
#     
#     So annotate the relevant functions to ensure stack protection is never
#     enabled for them.
#     
#     Fixes: 06ec27aea9fc ("powerpc/64: add stack protector support")
#     Cc: stable@vger.kernel.org # v4.20+
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20200316124421.99211-2-mpe@ellerman.id.au
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-gcc --version
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-ld --version
# < git log --format=%s --max-count=1 b86f6789c355a86ff6c3a8d5ab24774fd66a5a51
# < make -s -j 80 ARCH=alpha O=/kisskb/build/powerpc-next_alpha-defconfig_alpha-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-  defconfig
# < make -s -j 80 ARCH=alpha O=/kisskb/build/powerpc-next_alpha-defconfig_alpha-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-  help
# make -s -j 80 ARCH=alpha O=/kisskb/build/powerpc-next_alpha-defconfig_alpha-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-  olddefconfig
# make -s -j 80 ARCH=alpha O=/kisskb/build/powerpc-next_alpha-defconfig_alpha-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/alpha-linux/bin/alpha-linux-  
<stdin>:1511:2: warning: #warning syscall clone3 not implemented [-Wcpp]
/kisskb/src/fs/proc/inode.c: In function 'proc_reg_open':
/kisskb/src/include/linux/list.h:72:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c:338:21: note: 'pdeo' was declared here
/kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl':
/kisskb/src/kernel/printk/printk.c:204:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/io_uring.c: In function '__io_sqe_files_update':
/kisskb/src/fs/io_uring.c:5824:13: warning: 'err' may be used uninitialized in this function [-Wuninitialized]
WARNING: "saved_config" [vmlinux] is COMMON symbol
  Kernel arch/alpha/boot/vmlinux.gz is ready
Completed OK
# rm -rf /kisskb/build/powerpc-next_alpha-defconfig_alpha-gcc4.6
# Build took: 0:01:16.369031