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

[Anup Patel]

On Sun, May 24, 2020 at 2:26 PM Alexandre Ghiti <alex@xxxxxxxx> 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@xxxxxxxx>
> ---
>  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@xxxxxxxxxxxxxx>

Regards,
Anup