[v3,3/3] arch, scripts: Add script to check relocations at compile time

Relocating kernel at runtime is done very early in the boot process, so
it is not convenient to check for relocations there and react in case a
relocation was not expected.

Powerpc architecture has a script that allows to check at compile time
for such unexpected relocations: extract the common logic to scripts/
and add arch specific scripts triggered at postlink.

At the moment, powerpc and riscv architectures take advantage of this
compile-time check.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
 arch/powerpc/tools/relocs_check.sh | 18 ++-------------
 arch/riscv/Makefile.postlink       | 36 ++++++++++++++++++++++++++++++
 arch/riscv/tools/relocs_check.sh   | 26 +++++++++++++++++++++
 scripts/relocs_check.sh            | 20 +++++++++++++++++
 4 files changed, 84 insertions(+), 16 deletions(-)
 create mode 100644 arch/riscv/Makefile.postlink
 create mode 100755 arch/riscv/tools/relocs_check.sh
 create mode 100755 scripts/relocs_check.sh

On Sun, May 24, 2020 at 2:26 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Relocating kernel at runtime is done very early in the boot process, so
> it is not convenient to check for relocations there and react in case a
> relocation was not expected.
>
> Powerpc architecture has a script that allows to check at compile time
> for such unexpected relocations: extract the common logic to scripts/
> and add arch specific scripts triggered at postlink.
>
> At the moment, powerpc and riscv architectures take advantage of this
> compile-time check.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/powerpc/tools/relocs_check.sh | 18 ++-------------
>  arch/riscv/Makefile.postlink       | 36 ++++++++++++++++++++++++++++++
>  arch/riscv/tools/relocs_check.sh   | 26 +++++++++++++++++++++
>  scripts/relocs_check.sh            | 20 +++++++++++++++++
>  4 files changed, 84 insertions(+), 16 deletions(-)
>  create mode 100644 arch/riscv/Makefile.postlink
>  create mode 100755 arch/riscv/tools/relocs_check.sh
>  create mode 100755 scripts/relocs_check.sh

Maybe you should send the change arch/powerpc/tools/relocs_check.sh
as a separate patch so that it can be picked up by arch/powerpc maintainers.

>
> diff --git a/arch/powerpc/tools/relocs_check.sh b/arch/powerpc/tools/relocs_check.sh
> index 014e00e74d2b..e367895941ae 100755
> --- a/arch/powerpc/tools/relocs_check.sh
> +++ b/arch/powerpc/tools/relocs_check.sh
> @@ -15,21 +15,8 @@ if [ $# -lt 3 ]; then
>         exit 1
>  fi
>
> -# Have Kbuild supply the path to objdump and nm so we handle cross compilation.
> -objdump="$1"
> -nm="$2"
> -vmlinux="$3"
> -
> -# Remove from the bad relocations those that match an undefined weak symbol
> -# which will result in an absolute relocation to 0.
> -# Weak unresolved symbols are of that form in nm output:
> -# "                  w _binary__btf_vmlinux_bin_end"
> -undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
> -
>  bad_relocs=$(
> -$objdump -R "$vmlinux" |
> -       # Only look at relocation lines.
> -       grep -E '\<R_' |
> +${srctree}/scripts/relocs_check.sh "$@" |
>         # These relocations are okay
>         # On PPC64:
>         #       R_PPC64_RELATIVE, R_PPC64_NONE
> @@ -43,8 +30,7 @@ R_PPC_ADDR16_LO
>  R_PPC_ADDR16_HI
>  R_PPC_ADDR16_HA
>  R_PPC_RELATIVE
> -R_PPC_NONE' |
> -       ([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
> +R_PPC_NONE'
>  )
>
>  if [ -z "$bad_relocs" ]; then
> diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
> new file mode 100644
> index 000000000000..bf2b2bca1845
> --- /dev/null
> +++ b/arch/riscv/Makefile.postlink
> @@ -0,0 +1,36 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# ===========================================================================
> +# Post-link riscv pass
> +# ===========================================================================
> +#
> +# Check that vmlinux relocations look sane
> +
> +PHONY := __archpost
> +__archpost:
> +
> +-include include/config/auto.conf
> +include scripts/Kbuild.include
> +
> +quiet_cmd_relocs_check = CHKREL  $@
> +cmd_relocs_check =                                                     \
> +       $(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
> +
> +# `@true` prevents complaint when there is nothing to be done
> +
> +vmlinux: FORCE
> +       @true
> +ifdef CONFIG_RELOCATABLE
> +       $(call if_changed,relocs_check)
> +endif
> +
> +%.ko: FORCE
> +       @true
> +
> +clean:
> +       @true
> +
> +PHONY += FORCE clean
> +
> +FORCE:
> +
> +.PHONY: $(PHONY)
> diff --git a/arch/riscv/tools/relocs_check.sh b/arch/riscv/tools/relocs_check.sh
> new file mode 100755
> index 000000000000..baeb2e7b2290
> --- /dev/null
> +++ b/arch/riscv/tools/relocs_check.sh
> @@ -0,0 +1,26 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +# Based on powerpc relocs_check.sh
> +
> +# This script checks the relocations of a vmlinux for "suspicious"
> +# relocations.
> +
> +if [ $# -lt 3 ]; then
> +        echo "$0 [path to objdump] [path to nm] [path to vmlinux]" 1>&2
> +        exit 1
> +fi
> +
> +bad_relocs=$(
> +${srctree}/scripts/relocs_check.sh "$@" |
> +       # These relocations are okay
> +       #       R_RISCV_RELATIVE
> +       grep -F -w -v 'R_RISCV_RELATIVE'
> +)
> +
> +if [ -z "$bad_relocs" ]; then
> +       exit 0
> +fi
> +
> +num_bad=$(echo "$bad_relocs" | wc -l)
> +echo "WARNING: $num_bad bad relocations"
> +echo "$bad_relocs"
> diff --git a/scripts/relocs_check.sh b/scripts/relocs_check.sh
> new file mode 100755
> index 000000000000..137c660499f3
> --- /dev/null
> +++ b/scripts/relocs_check.sh
> @@ -0,0 +1,20 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +
> +# Get a list of all the relocations, remove from it the relocations
> +# that are known to be legitimate and return this list to arch specific
> +# script that will look for suspicious relocations.
> +
> +objdump="$1"
> +nm="$2"
> +vmlinux="$3"
> +
> +# Remove from the possible bad relocations those that match an undefined
> +# weak symbol which will result in an absolute relocation to 0.
> +# Weak unresolved symbols are of that form in nm output:
> +# "                  w _binary__btf_vmlinux_bin_end"
> +undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
> +
> +$objdump -R "$vmlinux" |
> +       grep -E '\<R_' |
> +       ([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
> --
> 2.20.1
>

Otherwise, looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup