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Ard Biesheuveltorvalds
Ard Biesheuvel
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torvalds
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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>
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‎init/Kconfig

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1987,6 +1987,10 @@ config MODVERSIONS
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make them incompatible with the kernel you are running. If
19881988
unsure, say N.
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config MODULE_REL_CRCS
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bool
1992+
depends on MODVERSIONS
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config MODULE_SRCVERSION_ALL
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bool "Source checksum for all modules"
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help

‎scripts/Makefile.build

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -164,6 +164,7 @@ cmd_gensymtypes_c = \
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$(CPP) -D__GENKSYMS__ $(c_flags) $< | \
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$(GENKSYMS) $(if $(1), -T $(2)) \
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$(patsubst y,-s _,$(CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX)) \
167+
$(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS)) \
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$(if $(KBUILD_PRESERVE),-p) \
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-r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))
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@@ -337,6 +338,7 @@ cmd_gensymtypes_S = \
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$(CPP) -D__GENKSYMS__ $(c_flags) -xc - | \
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$(GENKSYMS) $(if $(1), -T $(2)) \
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$(patsubst y,-s _,$(CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX)) \
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$(patsubst y,-R,$(CONFIG_MODULE_REL_CRCS)) \
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$(if $(KBUILD_PRESERVE),-p) \
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-r $(firstword $(wildcard $(2:.symtypes=.symref) /dev/null))
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‎scripts/genksyms/genksyms.c

Lines changed: 14 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -44,7 +44,7 @@ char *cur_filename, *source_file;
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int in_source_file;
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static int flag_debug, flag_dump_defs, flag_reference, flag_dump_types,
47-
flag_preserve, flag_warnings;
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flag_preserve, flag_warnings, flag_rel_crcs;
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static const char *mod_prefix = "";
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static int errors;
@@ -693,7 +693,10 @@ void export_symbol(const char *name)
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fputs(">\n", debugfile);
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/* Used as a linker script. */
696-
printf("%s__crc_%s = 0x%08lx ;\n", mod_prefix, name, crc);
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printf(!flag_rel_crcs ? "%s__crc_%s = 0x%08lx;\n" :
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"SECTIONS { .rodata : ALIGN(4) { "
698+
"%s__crc_%s = .; LONG(0x%08lx); } }\n",
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mod_prefix, name, crc);
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}
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}
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@@ -730,7 +733,7 @@ void error_with_pos(const char *fmt, ...)
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static void genksyms_usage(void)
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{
733-
fputs("Usage:\n" "genksyms [-adDTwqhV] > /path/to/.tmp_obj.ver\n" "\n"
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fputs("Usage:\n" "genksyms [-adDTwqhVR] > /path/to/.tmp_obj.ver\n" "\n"
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#ifdef __GNU_LIBRARY__
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" -s, --symbol-prefix Select symbol prefix\n"
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" -d, --debug Increment the debug level (repeatable)\n"
@@ -742,6 +745,7 @@ static void genksyms_usage(void)
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" -q, --quiet Disable warnings (default)\n"
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" -h, --help Print this message\n"
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" -V, --version Print the release version\n"
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" -R, --relative-crc Emit section relative symbol CRCs\n"
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#else /* __GNU_LIBRARY__ */
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" -s Select symbol prefix\n"
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" -d Increment the debug level (repeatable)\n"
@@ -753,6 +757,7 @@ static void genksyms_usage(void)
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" -q Disable warnings (default)\n"
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" -h Print this message\n"
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" -V Print the release version\n"
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" -R Emit section relative symbol CRCs\n"
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#endif /* __GNU_LIBRARY__ */
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, stderr);
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}
@@ -774,13 +779,14 @@ int main(int argc, char **argv)
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{"preserve", 0, 0, 'p'},
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{"version", 0, 0, 'V'},
776781
{"help", 0, 0, 'h'},
782+
{"relative-crc", 0, 0, 'R'},
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{0, 0, 0, 0}
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};
779785

780-
while ((o = getopt_long(argc, argv, "s:dwqVDr:T:ph",
786+
while ((o = getopt_long(argc, argv, "s:dwqVDr:T:phR",
781787
&long_opts[0], NULL)) != EOF)
782788
#else /* __GNU_LIBRARY__ */
783-
while ((o = getopt(argc, argv, "s:dwqVDr:T:ph")) != EOF)
789+
while ((o = getopt(argc, argv, "s:dwqVDr:T:phR")) != EOF)
784790
#endif /* __GNU_LIBRARY__ */
785791
switch (o) {
786792
case 's':
@@ -823,6 +829,9 @@ int main(int argc, char **argv)
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case 'h':
824830
genksyms_usage();
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return 0;
832+
case 'R':
833+
flag_rel_crcs = 1;
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break;
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default:
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genksyms_usage();
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return 1;

‎scripts/kallsyms.c

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -219,6 +219,10 @@ static int symbol_valid(struct sym_entry *s)
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"_SDA2_BASE_", /* ppc */
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NULL };
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222+
static char *special_prefixes[] = {
223+
"__crc_", /* modversions */
224+
NULL };
225+
222226
static char *special_suffixes[] = {
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"_veneer", /* arm */
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"_from_arm", /* arm */
@@ -259,6 +263,14 @@ static int symbol_valid(struct sym_entry *s)
259263
if (strcmp(sym_name, special_symbols[i]) == 0)
260264
return 0;
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266+
for (i = 0; special_prefixes[i]; i++) {
267+
int l = strlen(special_prefixes[i]);
268+
269+
if (l <= strlen(sym_name) &&
270+
strncmp(sym_name, special_prefixes[i], l) == 0)
271+
return 0;
272+
}
273+
262274
for (i = 0; special_suffixes[i]; i++) {
263275
int l = strlen(sym_name) - strlen(special_suffixes[i]);
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‎scripts/mod/modpost.c

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -621,6 +621,16 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
621621
if (strncmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
622622
is_crc = true;
623623
crc = (unsigned int) sym->st_value;
624+
if (sym->st_shndx != SHN_UNDEF && sym->st_shndx != SHN_ABS) {
625+
unsigned int *crcp;
626+
627+
/* symbol points to the CRC in the ELF object */
628+
crcp = (void *)info->hdr + sym->st_value +
629+
info->sechdrs[sym->st_shndx].sh_offset -
630+
(info->hdr->e_type != ET_REL ?
631+
info->sechdrs[sym->st_shndx].sh_addr : 0);
632+
crc = *crcp;
633+
}
624634
sym_update_crc(symname + strlen(CRC_PFX), mod, crc,
625635
export);
626636
}

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