Re: [PATCH v6 00/29] Warn on orphan section placement

From: Kees Cook
Date: Mon Aug 31 2020 - 15:41:28 EST

On Fri, Aug 21, 2020 at 12:42:41PM -0700, Kees Cook wrote:
> Hi Ingo,
>
> Based on my testing, this is ready to go. I've reviewed the feedback on
> v5 and made a few small changes, noted below.

If no one objects, I'll pop this into my tree for -next. I'd prefer it
go via -tip though! :)

Thanks!

-Kees

>
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=linker/orphans/warn/v6
>
> v6:
> - rebase to -tip x86/boot
> - remove 0-sized NOLOAD
> - move .got.plt to end with INFO (NOLOAD warns)
> - add Reviewed-bys
> v5: https://lore.kernel.org/lkml/20200731230820.1742553-1-keescook@xxxxxxxxxxxx/
> v4: https://lore.kernel.org/lkml/20200629061840.4065483-1-keescook@xxxxxxxxxxxx/
> v3: https://lore.kernel.org/lkml/20200624014940.1204448-1-keescook@xxxxxxxxxxxx/
> v2: https://lore.kernel.org/lkml/20200622205815.2988115-1-keescook@xxxxxxxxxxxx/
> v1: https://lore.kernel.org/lkml/20200228002244.15240-1-keescook@xxxxxxxxxxxx/
>
> 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: -tip x86/boot
>
> All three architectures depend on the first several commits to
> vmlinux.lds.h. x86 depends on Arvind's GOT series (in -tip x86/boot now).
> arm64 depends on the efi/libstub patch. As such, I'd like to land this
> series as a whole. Ingo has suggested he'd take it into -tip.
>
> Thanks!
>
> -Kees
>
> [1] https://github.com/ClangBuiltLinux/linux/issues/282
> [2] https://lore.kernel.org/lkml/202002242122.AA4D1B8@keescook/
>
> 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: Assert for unwanted 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
>
> 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 | 30 ++++++++--
> 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/x86/Makefile | 4 ++
> arch/x86/boot/compressed/Makefile | 2 +
> arch/x86/boot/compressed/vmlinux.lds.S | 58 +++++++++++++------
> arch/x86/include/asm/asm.h | 6 +-
> arch/x86/kernel/vmlinux.lds.S | 39 ++++++++++++-
> drivers/firmware/efi/libstub/Makefile | 9 ++-
> include/asm-generic/vmlinux.lds.h | 49 +++++++++++++---
> 35 files changed, 241 insertions(+), 60 deletions(-)
> rename arch/arm/{kernel => include/asm}/vmlinux.lds.h (84%)
>
> --
> 2.25.1
>

--
Kees Cook