# git rev-parse -q --verify 478036c4cd1a16e613a2f883d79c03cf187faacb^{commit}
478036c4cd1a16e613a2f883d79c03cf187faacb
already have revision, skipping fetch
# git checkout -q -f -B kisskb 478036c4cd1a16e613a2f883d79c03cf187faacb
# git clean -qxdf
# < git log -1
# commit 478036c4cd1a16e613a2f883d79c03cf187faacb
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Mon Jun 14 23:14:40 2021 +1000
# 
#     powerpc: Fix initrd corruption with relative jump labels
#     
#     Commit b0b3b2c78ec0 ("powerpc: Switch to relative jump labels") switched
#     us to using relative jump labels. That involves changing the code,
#     target and key members in struct jump_entry to be relative to the
#     address of the jump_entry, rather than absolute addresses.
#     
#     We have two static inlines that create a struct jump_entry,
#     arch_static_branch() and arch_static_branch_jump(), as well as an asm
#     macro ARCH_STATIC_BRANCH, which is used by the pseries-only hypervisor
#     tracing code.
#     
#     Unfortunately we missed updating the key to be a relative reference in
#     ARCH_STATIC_BRANCH.
#     
#     That causes a pseries kernel to have a handful of jump_entry structs
#     with bad key values. Instead of being a relative reference they instead
#     hold the full address of the key.
#     
#     However the code doesn't expect that, it still adds the key value to the
#     address of the jump_entry (see jump_entry_key()) expecting to get a
#     pointer to a key somewhere in kernel data.
#     
#     The table of jump_entry structs sits in rodata, which comes after the
#     kernel text. In a typical build this will be somewhere around 15MB. The
#     address of the key will be somewhere in data, typically around 20MB.
#     Adding the two values together gets us a pointer somewhere around 45MB.
#     
#     We then call static_key_set_entries() with that bad pointer and modify
#     some members of the struct static_key we think we are pointing at.
#     
#     A pseries kernel is typically ~30MB in size, so writing to ~45MB won't
#     corrupt the kernel itself. However if we're booting with an initrd,
#     depending on the size and exact location of the initrd, we can corrupt
#     the initrd. Depending on how exactly we corrupt the initrd it can either
#     cause the system to not boot, or just corrupt one of the files in the
#     initrd.
#     
#     The fix is simply to make the key value relative to the jump_entry
#     struct in the ARCH_STATIC_BRANCH macro.
#     
#     Fixes: b0b3b2c78ec0 ("powerpc: Switch to relative jump labels")
#     Reported-by: Anastasia Kovaleva <a.kovaleva@yadro.com>
#     Reported-by: Roman Bolshakov <r.bolshakov@yadro.com>
#     Reported-by: Greg Kurz <groug@kaod.org>
#     Reported-by: Daniel Axtens <dja@axtens.net>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Tested-by: Daniel Axtens <dja@axtens.net>
#     Tested-by: Greg Kurz <groug@kaod.org>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20210614131440.312360-1-mpe@ellerman.id.au
# < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 478036c4cd1a16e613a2f883d79c03cf187faacb
# < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig+NO_HUGETLB+4K_PAGES_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  ppc64_defconfig
# Added to kconfig CONFIG_PPC_64K_PAGES=n
# Added to kconfig CONFIG_PPC_4K_PAGES=y
# Added to kconfig CONFIG_HUGETLBFS=n
# < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig+NO_HUGETLB+4K_PAGES_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig+NO_HUGETLB+4K_PAGES_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
.config:4415:warning: override: reassigning to symbol PPC_4K_PAGES
# make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig+NO_HUGETLB+4K_PAGES_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_ppc64_defconfig+NO_HUGETLB+4K_PAGES_powerpc-gcc9
# Build took: 0:02:37.332210