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kbuild: modversions: add infrastructure for emitting relative CRCs 

This add the kbuild infrastructure that will allow architectures to emit
vmlinux symbol CRCs as 32-bit offsets to another location in the kernel
where the actual value is stored. This works around problems with CRCs
being mistaken for relocatable symbols on kernels that self relocate at
runtime (i.e., powerpc with CONFIG_RELOCATABLE=y)

For the kbuild side of things, this comes down to the following:

 - introducing a Kconfig symbol MODULE_REL_CRCS

 - adding a -R switch to genksyms to instruct it to emit the CRC symbols
   as references into the .rodata section

 - making modpost distinguish such references from absolute CRC symbols
   by the section index (SHN_ABS)

 - making kallsyms disregard non-absolute symbols with a __crc_ prefix

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ard Biesheuvel 2017-02-03 09:54:05 +00:00 committed by Linus Torvalds
parent 34e00accf6
commit 56067812d5
5 changed files with 42 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
init/Kconfig
View File

@ -1987,6 +1987,10 @@ config MODVERSIONS
make them incompatible with the kernel you are running. If
unsure, say N.
config MODULE_REL_CRCS
bool
depends on MODVERSIONS
config MODULE_SRCVERSION_ALL
bool "Source checksum for all modules"
help

2
scripts/Makefile.build
View File

@ -164,6 +164,7 @@ cmd_gensymtypes_c = \
$(CPP) -D__GENKSYMS__ $(c_flags) $< | \
$(GENKSYMS) $(if $(1), -T $(2)) \
$(patsubst y,-s _,$(CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX)) \
$(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS)) \
$(if $(KBUILD_PRESERVE),-p) \
-r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))
@ -337,6 +338,7 @@ cmd_gensymtypes_S = \
$(CPP) -D__GENKSYMS__ $(c_flags) -xc - | \
$(GENKSYMS) $(if $(1), -T $(2)) \
$(patsubst y,-s _,$(CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX)) \
$(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS)) \
$(if $(KBUILD_PRESERVE),-p) \
-r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))

19
scripts/genksyms/genksyms.c
View File

@ -44,7 +44,7 @@ char *cur_filename, *source_file;
int in_source_file;
static int flag_debug, flag_dump_defs, flag_reference, flag_dump_types,
flag_preserve, flag_warnings;
flag_preserve, flag_warnings, flag_rel_crcs;
static const char *mod_prefix = "";
static int errors;
@ -693,7 +693,10 @@ void export_symbol(const char *name)
fputs(">\n", debugfile);
/* Used as a linker script. */
printf("%s__crc_%s = 0x%08lx ;\n", mod_prefix, name, crc);
printf(!flag_rel_crcs ? "%s__crc_%s = 0x%08lx;\n" :
"SECTIONS { .rodata : ALIGN(4) { "
"%s__crc_%s = .; LONG(0x%08lx); } }\n",
mod_prefix, name, crc);
}
}
@ -730,7 +733,7 @@ void error_with_pos(const char *fmt, ...)
static void genksyms_usage(void)
{
fputs("Usage:\n" "genksyms [-adDTwqhV] > /path/to/.tmp_obj.ver\n" "\n"
fputs("Usage:\n" "genksyms [-adDTwqhVR] > /path/to/.tmp_obj.ver\n" "\n"
#ifdef __GNU_LIBRARY__
" -s, --symbol-prefix Select symbol prefix\n"
" -d, --debug Increment the debug level (repeatable)\n"
@ -742,6 +745,7 @@ static void genksyms_usage(void)
" -q, --quiet Disable warnings (default)\n"
" -h, --help Print this message\n"
" -V, --version Print the release version\n"
" -R, --relative-crc Emit section relative symbol CRCs\n"
#else /* __GNU_LIBRARY__ */
" -s Select symbol prefix\n"
" -d Increment the debug level (repeatable)\n"
@ -753,6 +757,7 @@ static void genksyms_usage(void)
" -q Disable warnings (default)\n"
" -h Print this message\n"
" -V Print the release version\n"
" -R Emit section relative symbol CRCs\n"
#endif /* __GNU_LIBRARY__ */
, stderr);
}
@ -774,13 +779,14 @@ int main(int argc, char **argv)
{"preserve", 0, 0, 'p'},
{"version", 0, 0, 'V'},
{"help", 0, 0, 'h'},
{"relative-crc", 0, 0, 'R'},
{0, 0, 0, 0}
};
while ((o = getopt_long(argc, argv, "s:dwqVDr:T:ph",
while ((o = getopt_long(argc, argv, "s:dwqVDr:T:phR",
&long_opts[0], NULL)) != EOF)
#else /* __GNU_LIBRARY__ */
while ((o = getopt(argc, argv, "s:dwqVDr:T:ph")) != EOF)
while ((o = getopt(argc, argv, "s:dwqVDr:T:phR")) != EOF)
#endif /* __GNU_LIBRARY__ */
switch (o) {
case 's':
@ -823,6 +829,9 @@ int main(int argc, char **argv)
case 'h':
genksyms_usage();
return 0;
case 'R':
flag_rel_crcs = 1;
break;
default:
genksyms_usage();
return 1;

12
scripts/kallsyms.c
View File

@ -219,6 +219,10 @@ static int symbol_valid(struct sym_entry *s)
"_SDA2_BASE_", /* ppc */
NULL };
static char *special_prefixes[] = {
"__crc_", /* modversions */
NULL };
static char *special_suffixes[] = {
"_veneer", /* arm */
"_from_arm", /* arm */
@ -259,6 +263,14 @@ static int symbol_valid(struct sym_entry *s)
if (strcmp(sym_name, special_symbols[i]) == 0)
return 0;
for (i = 0; special_prefixes[i]; i++) {
int l = strlen(special_prefixes[i]);
if (l <= strlen(sym_name) &&
strncmp(sym_name, special_prefixes[i], l) == 0)
return 0;
}
for (i = 0; special_suffixes[i]; i++) {
int l = strlen(sym_name) - strlen(special_suffixes[i]);

10
scripts/mod/modpost.c
View File

@ -621,6 +621,16 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
if (strncmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
is_crc = true;
crc = (unsigned int) sym->st_value;
if (sym->st_shndx != SHN_UNDEF && sym->st_shndx != SHN_ABS) {
unsigned int *crcp;
/* symbol points to the CRC in the ELF object */
crcp = (void *)info->hdr + sym->st_value +
info->sechdrs[sym->st_shndx].sh_offset -
(info->hdr->e_type != ET_REL ?
info->sechdrs[sym->st_shndx].sh_addr : 0);
crc = *crcp;
}
sym_update_crc(symname + strlen(CRC_PFX), mod, crc,
export);
}