linux-kernel - Re: [PATCH v4 14/17] arm/build: Warn on orphan section placement

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Date:   Mon, 29 Jun 2020 12:47:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 14/17] arm/build: Warn on orphan section placement

On Sun, Jun 28, 2020 at 11:18 PM Kees Cook <keescook@...omium.org> wrote:
>
> We don't want to depend on the linker's orphan section placement
> heuristics as these can vary between linkers, and may change between
> versions. All sections need to be explicitly named in the linker
> script.
>
> Specifically, this would have made a recently fixed bug very obvious:
>
> ld: warning: orphan section `.fixup' from `arch/arm/lib/copy_from_user.o' being placed in section `.fixup'
>
> Discard unneeded sections .iplt, .rel.iplt, .igot.plt, and .modinfo.
>
> Add missing text stub sections .vfp11_veneer and .v4_bx.
>
> Add debug sections explicitly.
>
> Finally enable orphan section warning.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Thanks for following up on the previous suggestion regarding .glu_7 /
.glu_7t ordering. LGTM
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  arch/arm/include/asm/vmlinux.lds.h | 6 +++++-
>  arch/arm/kernel/vmlinux-xip.lds.S  | 1 +
>  arch/arm/kernel/vmlinux.lds.S      | 1 +
>  3 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h
> index c66b16cd8837..d44fae722e7a 100644
> --- a/arch/arm/include/asm/vmlinux.lds.h
> +++ b/arch/arm/include/asm/vmlinux.lds.h
> @@ -39,6 +39,8 @@
>                 __idmap_text_end = .;                                   \
>
>  #define ARM_COMMON_DISCARD                                             \
> +               *(.iplt) *(.rel.iplt) *(.igot.plt)                      \
> +               *(.modinfo)                                             \
>                 *(.discard)                                             \
>                 *(.discard.*)
>
> @@ -63,7 +65,9 @@
>  #define ARM_STUBS_TEXT                                                 \
>                 *(.gnu.warning)                                         \
>                 *(.glue_7)                                              \
> -               *(.glue_7t)
> +               *(.glue_7t)                                             \
> +               *(.vfp11_veneer)                                        \
> +               *(.v4_bx)
>
>  #define ARM_TEXT                                                       \
>                 IDMAP_TEXT                                              \
> diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
> index 57fcbf55f913..11ffa79751da 100644
> --- a/arch/arm/kernel/vmlinux-xip.lds.S
> +++ b/arch/arm/kernel/vmlinux-xip.lds.S
> @@ -150,6 +150,7 @@ SECTIONS
>         _end = .;
>
>         STABS_DEBUG
> +       DWARF_DEBUG
>         ARM_DETAILS
>  }
>
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index 1d3d3b599635..dc672fe35de3 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -149,6 +149,7 @@ SECTIONS
>         _end = .;
>
>         STABS_DEBUG
> +       DWARF_DEBUG
>         ARM_DETAILS
>  }
>
> --
> 2.25.1
>
> --
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-- 
Thanks,
~Nick Desaulniers