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[POWERPC] Discourage people from fiddling with kernel data from prom_init

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As BenH said the other day, it is an "accident" that prom_init.o is
linked with the rest of the kernel.  The truth is a little more
subtle, prom_init isn't truly bootloader, it does access kernel data
in a few places.

What we can do is discourage people from adding new code that accesses
data outside of prom_init.  And hence this patch; from the script:

 # This script checks prom_init.o to see what external symbols it
 # is using, if it finds symbols not in the whitelist it returns
 # an error. The point of this is to discourage people from
 # intentionally or accidentally adding new code to prom_init.c
 # which has side effects on other parts of the kernel.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Michael Ellerman 2008-04-24 12:08:22 +10:00 committed by Paul Mackerras
parent d9e9d82c24
commit 5c02cd2fb8
2 changed files with 67 additions and 0 deletions
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9
arch/powerpc/kernel/Makefile
View file

@ -106,4 +106,13 @@ PHONY += systbl_chk
systbl_chk: $(src)/systbl_chk.sh $(obj)/systbl_chk.i
$(call cmd,systbl_chk)
$(obj)/built-in.o: prom_init_check
quiet_cmd_prom_init_check = CALL $<
cmd_prom_init_check = $(CONFIG_SHELL) $< "$(NM)" "$(obj)/prom_init.o"
PHONY += prom_init_check
prom_init_check: $(src)/prom_init_check.sh $(obj)/prom_init.o
$(call cmd,prom_init_check)
clean-files := vmlinux.lds

58
arch/powerpc/kernel/prom_init_check.sh Normal file
View file

@ -0,0 +1,58 @@
#!/bin/sh
#
# Copyright © 2008 IBM Corporation
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version
# 2 of the License, or (at your option) any later version.
# This script checks prom_init.o to see what external symbols it
# is using, if it finds symbols not in the whitelist it returns
# an error. The point of this is to discourage people from
# intentionally or accidentally adding new code to prom_init.c
# which has side effects on other parts of the kernel.
# If you really need to reference something from prom_init.o add
# it to the list below:
WHITELIST="add_reloc_offset __bss_start __bss_stop copy_and_flush
_end enter_prom memcpy memset reloc_offset __secondary_hold
__secondary_hold_acknowledge __secondary_hold_spinloop __start
strcmp strcpy strlcpy strlen strncmp strstr logo_linux_clut224
reloc_got2"
NM="$1"
OBJ="$2"
ERROR=0
for UNDEF in $($NM -u $OBJ | awk '{print $2}')
do
# On 64-bit nm gives us the function descriptors, which have
# a leading . on the name, so strip it off here.
UNDEF="${UNDEF#.}"
if [ $KBUILD_VERBOSE ]; then
if [ $KBUILD_VERBOSE -ne 0 ]; then
echo "Checking prom_init.o symbol '$UNDEF'"
fi
fi
OK=0
for WHITE in $WHITELIST
do
if [ "$UNDEF" = "$WHITE" ]; then
OK=1
break
fi
done
if [ $OK -eq 0 ]; then
ERROR=1
echo "Error: External symbol '$UNDEF' referenced" \
"from prom_init.c" >&2
fi
done
exit $ERROR