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Subject[PATCH v3 0/9] add support for relative references in jump tables
This series implements support for emitting the data structures associated
with jump tables as 32-bit relative references instead of absolute
references, which take up more space on builds that target 64-bit
architectures, or implement self relocation [or both].

This series enables it for arm64 and x86, although other architectures
might benefit as well.

Patch #1 does some preparatory refactoring before patch #2 introduces the
generic pieces required for using relative references.

Patch #3 wires everything up for arm64.

Patch #4 introduces support for handling 64-bit place relative relocations
on x86_64 (see 'Changes since v1' below)

For x86, patch #5 applies some preparatory changes for the arch specific
jump label C code, which is a lot more involved than on arm64, which is
why it is split off in this case. Patch #6 wires it up for x86 as well.

Patch #7 and #8 implement the changes so that the jump_entry arrays reside
in ro_after_init memory rather than remain fully writable all of the time.

Patch #9 enables the feature for s390 (contributed by Heiko)

Changes since v2:
- fix breakage in user mode x86 kernel due to missing definition of the
R_X86_64_PC64 symbolic constant
- add acks from Jessica and Kees
- add s390 enablement patch

Changes since v1:
- change the relative reference to the static key to a 64-bit wide one on 64
bit architectures; this is necessary on arm64, which allows modules to
reside anywhere within a 4 GB window covering the core kernel text, which
means a 32-bit signed quantity with its +/- 2 GB range is insufficient.
Note that x86_64 changes are in preparation that widen the relocation
range as well (using the PIE linker), so I assumed that the same change
is appropriate for x86 as well.
- add patch #4 to handle the relocations emitted by the compiler as a result
of the change above
- added patches to move the jump_entry arrays to ro_after_init memory, so
that they are not as easily corrupted or manipulated.
- add Will's ack to patch #3

Cc: Arnd Bergmann <>
Cc: Heiko Carstens <>
Cc: Kees Cook <>
Cc: Will Deacon <>
Cc: Thomas Gleixner <>
Cc: Catalin Marinas <>
Cc: Ingo Molnar <>
Cc: Steven Rostedt <>
Cc: Martin Schwidefsky <>
Cc: Jessica Yu <>
Cc: Peter Zijlstra <>

Ard Biesheuvel (8):
kernel/jump_label: abstract jump_entry member accessors
kernel/jump_label: implement generic support for relative references
arm64/kernel: jump_label: switch to relative references
x86: add support for 64-bit place relative relocations
x86: jump_label: switch to jump_entry accessors
x86/kernel: jump_table: use relative references
jump_label: annotate entries that operate on __init code earlier
jump_table: move entries into ro_after_init region

Heiko Carstens (1):
s390/jump_label: switch to relative references

arch/Kconfig | 3 +
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/jump_label.h | 38 ++++----
arch/arm64/kernel/jump_label.c | 6 +-
arch/s390/Kconfig | 1 +
arch/s390/include/asm/jump_label.h | 40 ++++----
arch/s390/kernel/jump_label.c | 11 ++-
arch/s390/kernel/ | 1 +
arch/x86/Kconfig | 1 +
arch/x86/include/asm/elf.h | 3 +-
arch/x86/include/asm/jump_label.h | 24 ++---
arch/x86/kernel/jump_label.c | 62 +++++-------
arch/x86/kernel/module.c | 6 ++
arch/x86/tools/relocs.c | 10 ++
arch/x86/um/asm/elf.h | 3 +-
include/asm-generic/ | 11 ++-
include/linux/jump_label.h | 65 ++++++++++++-
init/main.c | 1 -
kernel/jump_label.c | 100 +++++++++-----------
kernel/module.c | 9 ++
tools/objtool/special.c | 4 +-
21 files changed, 226 insertions(+), 174 deletions(-)


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