linux-kernel - Re: [PATCH 0/9] Enable orphan section warning

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Message-ID: <CA+icZUVRnjOWKZynAGDniXD_H9KRccONmeKHs25DPPU1c8ZcGg@mail.gmail.com>
Date:   Fri, 28 Feb 2020 07:51:21 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Borislav Petkov <bp@...e.de>, "H.J. Lu" <hjl.tools@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kbuild@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] Enable orphan section warning

On Fri, Feb 28, 2020 at 1:22 AM Kees Cook <keescook@...omium.org> wrote:
>
> Hi!
>
> A recent bug 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. Similarly, the recent FGKASLR series brough up orphan
> section handling too[2]. In both 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 or discarded) with any orphans throwing a warning. The
> powerpc architecture actually already does this, so this series seeks
> to extend this coverage to x86, arm64, and arm.
>
> This series depends on tip/x86/boot (where recent .eh_frame fixes[3]
> landed), and has a minor conflict[4] with the ARM tree (related to
> the earlier mentioned bug). As it uses refactorings in the asm-generic
> linker script, and makes changes to kbuild, I think the cleanest place
> for this series to land would also be through -tip. Once again (like
> my READ_IMPLIES_EXEC series), I'm looking to get maintainer Acks so
> this can go all together with the least disruption. Splitting it up by
> architecture seems needlessly difficult.
>
> 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/158264960194.28353.10560165361470246192.tip-bot2@tip-bot2/
> [4] https://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8959/1
>

Hi Kees,

is this an updated version of what you have in your
kees/linux.git#linker/orphans/x86-arm Git branch?

Especially, I saw a difference in [2] and "[PATCH 4/9] x86/boot: Warn
on orphan section placement"

[ arch/x86/boot/compressed/Makefile ]

+KBUILD_LDFLAGS += --no-ld-generated-unwind-info

Can you comment on why this KBUILD_LDFLAGS was added/needed?

I like when people offer their work in a Git branch.
Do you plan to do that?

Thanks.

Regards,
- Sedat -

[1] https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=linker/orphans/x86-arm
[2] https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=linker/orphans/x86-arm&id=e43aa77956c40b9b6db0b37b3780423aa2e661ad



> H.J. Lu (1):
>   Add RUNTIME_DISCARD_EXIT to generic DISCARDS
>
> Kees Cook (8):
>   scripts/link-vmlinux.sh: Delay orphan handling warnings until final
>     link
>   vmlinux.lds.h: Add .gnu.version* to DISCARDS
>   x86/build: Warn on orphan section placement
>   x86/boot: Warn on orphan section placement
>   arm64/build: Use common DISCARDS in linker script
>   arm64/build: Warn on orphan section placement
>   arm/build: Warn on orphan section placement
>   arm/boot: Warn on orphan section placement
>
>  arch/arm/Makefile                             |  4 ++++
>  arch/arm/boot/compressed/Makefile             |  2 ++
>  arch/arm/boot/compressed/vmlinux.lds.S        | 17 ++++++--------
>  .../arm/{kernel => include/asm}/vmlinux.lds.h | 22 ++++++++++++++-----
>  arch/arm/kernel/vmlinux-xip.lds.S             |  5 ++---
>  arch/arm/kernel/vmlinux.lds.S                 |  5 ++---
>  arch/arm64/Makefile                           |  4 ++++
>  arch/arm64/kernel/vmlinux.lds.S               | 13 +++++------
>  arch/x86/Makefile                             |  4 ++++
>  arch/x86/boot/compressed/Makefile             |  3 ++-
>  arch/x86/boot/compressed/vmlinux.lds.S        | 13 +++++++++++
>  arch/x86/kernel/vmlinux.lds.S                 |  7 ++++++
>  include/asm-generic/vmlinux.lds.h             | 11 ++++++++--
>  scripts/link-vmlinux.sh                       |  6 +++++
>  14 files changed, 85 insertions(+), 31 deletions(-)
>  rename arch/arm/{kernel => include/asm}/vmlinux.lds.h (92%)
>
> --
> 2.20.1
>
> --
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