[PATCH v5 00/36] Warn on orphan section placement

Kees Cook
2020-07-31T23:08:34Z

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=linker/orphans/warn/v5

v5:
- rebase from -rc2 to -rc7 to avoid build failures on Clang vs binutils
- include Arvind's GOT fix-up series[3], since it touches many similar areas
- add PGO/AutoFDO section patch[4]
- split up x86 and arm changes into more digestable steps
- move several sections out of DISCARD and into zero-size asserts
- introduce COMMON_DISCARDS to improve ARM's linker scripts
v4: https://lore.kernel.org/lkml/20200629061840.4065483-1-keescook@chromium.org/
v3: https://lore.kernel.org/lkml/20200624014940.1204448-1-keescook@chromium.org/
v2: https://lore.kernel.org/lkml/20200622205815.2988115-1-keescook@chromium.org/
v1: https://lore.kernel.org/lkml/20200228002244.15240-1-keescook@chromium.org/

A recent bug[1] was solved for builds linked with ld.lld, and tracking
it down took way longer than it needed to (a year). Ultimately, it
boiled down to differences between ld.bfd and ld.lld's handling of
orphan sections. Similar situation have continued to recur, and it's
clear the kernel build needs to be much more explicit about linker
sections. Similarly, the recent FGKASLR series brought up orphan section
handling too[2]. In all cases, it would have been nice if the linker was
running with --orphan-handling=warn so that surprise sections wouldn't
silently get mapped into the kernel image at locations up to the whim
of the linker's orphan handling logic. Instead, all desired sections
should be explicitly identified in the linker script (to be either kept,
discarded, or verified to be zero-sized) with any orphans throwing a
warning. The powerpc architecture has actually been doing this for some
time, so this series just extends that coverage to x86, arm, and arm64.

This has gotten sucecssful build testing under the following matrix:

compiler/linker: gcc+ld.bfd, clang+ld.lld
targets: defconfig, allmodconfig
architectures: x86, i386, arm64, arm
versions: v5.8-rc7, next-20200731 (with various build fixes[7][8])

Two known-failure exceptions (unchanged by this series) being:
- clang+arm/arm64 needs CONFIG_CPU_BIG_ENDIAN=n to pass allmodconfig[5]
- clang+i386 only builds in -next, which was recently fixed[6]

All three architectures depend on the first several commits to
vmlinux.lds.h. x86 depends on Arvind's GOT series[3], so I collected it
into this version of my series, as it hadn't been taken into -tip yet.
arm64 depends on the efi/libstub patch. As such, I'd like to land this
series as a whole. Given that two thirds of it is in the arm universe,
perhaps this can land via the arm64 tree? If x86 -tip is preferred, that
works too. If I don't hear otherwise, I will just carry this myself in
-next. In all cases, I would really appreciate reviews/acks/etc. :)

Thanks!

-Kees

[1] https://github.com/ClangBuiltLinux/linux/issues/282
[2] https://lore.kernel.org/lkml/202002242122.AA4D1B8@keescook/
[3] https://lore.kernel.org/lkml/20200715004133.1430068-1-nivedita@alum.mit.edu/
[4] https://lore.kernel.org/lkml/20200625184752.73095-1-ndesaulniers@google.com/
[5] https://github.com/ClangBuiltLinux/linux/issues/1071
[6] https://github.com/ClangBuiltLinux/linux/issues/194
[7] https://lore.kernel.org/lkml/1596166744-2954-2-git-send-email-neal.liu@mediatek.com/
[8] https://lore.kernel.org/lkml/82f750c4-d423-1ed8-a158-e75153745e07@huawei.com/

Ard Biesheuvel (3):
x86/boot/compressed: Move .got.plt entries out of the .got section
x86/boot/compressed: Force hidden visibility for all symbol references
x86/boot/compressed: Get rid of GOT fixup code

Arvind Sankar (4):
x86/boot: Add .text.* to setup.ld
x86/boot: Remove run-time relocations from .head.text code
x86/boot: Remove run-time relocations from head_{32,64}.S
x86/boot: Check that there are no run-time relocations

Kees Cook (28):
vmlinux.lds.h: Create COMMON_DISCARDS
vmlinux.lds.h: Add .gnu.version* to COMMON_DISCARDS
vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections
vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG
vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS
efi/libstub: Disable -mbranch-protection
arm64/mm: Remove needless section quotes
arm64/kernel: Remove needless Call Frame Information annotations
arm64/build: Remove .eh_frame* sections due to unwind tables
arm64/build: Use common DISCARDS in linker script
arm64/build: Add missing DWARF sections
arm64/build: Assert for unwanted sections
arm64/build: Warn on orphan section placement
arm/build: Refactor linker script headers
arm/build: Explicitly keep .ARM.attributes sections
arm/build: Add missing sections
arm/build: Warn on orphan section placement
arm/boot: Handle all sections explicitly
arm/boot: Warn on orphan section placement
x86/asm: Avoid generating unused kprobe sections
x86/build: Enforce an empty .got.plt section
x86/build: Assert for unwanted sections
x86/build: Warn on orphan section placement
x86/boot/compressed: Reorganize zero-size section asserts
x86/boot/compressed: Remove, discard, or assert for unwanted sections
x86/boot/compressed: Add missing debugging sections to output
x86/boot/compressed: Warn on orphan section placement
arm/build: Assert for unwanted sections

Nick Desaulniers (1):
vmlinux.lds.h: add PGO and AutoFDO input sections

arch/alpha/kernel/vmlinux.lds.S | 1 +
arch/arc/kernel/vmlinux.lds.S | 1 +
arch/arm/Makefile | 4 +
arch/arm/boot/compressed/Makefile | 2 +
arch/arm/boot/compressed/vmlinux.lds.S | 20 +--
.../arm/{kernel => include/asm}/vmlinux.lds.h | 29 ++-
arch/arm/kernel/vmlinux-xip.lds.S | 8 +-
arch/arm/kernel/vmlinux.lds.S | 8 +-
arch/arm64/Makefile | 9 +-
arch/arm64/kernel/smccc-call.S | 2 -
arch/arm64/kernel/vmlinux.lds.S | 28 ++-
arch/arm64/mm/mmu.c | 2 +-
arch/csky/kernel/vmlinux.lds.S | 1 +
arch/hexagon/kernel/vmlinux.lds.S | 1 +
arch/ia64/kernel/vmlinux.lds.S | 1 +
arch/mips/kernel/vmlinux.lds.S | 1 +
arch/nds32/kernel/vmlinux.lds.S | 1 +
arch/nios2/kernel/vmlinux.lds.S | 1 +
arch/openrisc/kernel/vmlinux.lds.S | 1 +
arch/parisc/boot/compressed/vmlinux.lds.S | 1 +
arch/parisc/kernel/vmlinux.lds.S | 1 +
arch/powerpc/kernel/vmlinux.lds.S | 2 +-
arch/riscv/kernel/vmlinux.lds.S | 1 +
arch/s390/kernel/vmlinux.lds.S | 1 +
arch/sh/kernel/vmlinux.lds.S | 1 +
arch/sparc/kernel/vmlinux.lds.S | 1 +
arch/um/kernel/dyn.lds.S | 2 +-
arch/um/kernel/uml.lds.S | 2 +-
arch/unicore32/kernel/vmlinux.lds.S | 1 +
arch/x86/Makefile | 4 +
arch/x86/boot/compressed/Makefile | 41 +----
arch/x86/boot/compressed/head_32.S | 99 ++++-------
arch/x86/boot/compressed/head_64.S | 165 +++++++-----------
arch/x86/boot/compressed/mkpiggy.c | 6 +
arch/x86/boot/compressed/vmlinux.lds.S | 48 ++++-
arch/x86/boot/setup.ld | 2 +-
arch/x86/include/asm/asm.h | 6 +-
arch/x86/kernel/vmlinux.lds.S | 39 ++++-
drivers/firmware/efi/libstub/Makefile | 11 +-
drivers/firmware/efi/libstub/hidden.h | 6 -
include/asm-generic/vmlinux.lds.h | 49 +++++-
include/linux/hidden.h | 19 ++
42 files changed, 377 insertions(+), 252 deletions(-)
rename arch/arm/{kernel => include/asm}/vmlinux.lds.h (84%)
delete mode 100644 drivers/firmware/efi/libstub/hidden.h
create mode 100644 include/linux/hidden.h

--
2.25.1