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UBUNTU: SAUCE: modpost: support arbitrary symbol length in modversion

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BugLink: https://bugs.launchpad.net/bugs/2007654

Currently modversion uses a fixed size array of size (64 - sizeof(long))
to store symbol names, thus placing a hard limit on length of symbols.
Rust symbols (which encodes crate and module names) can be quite a bit
longer. The length limit in kallsyms is increased to 512 for this reason.

It's a waste of space to simply expand the fixed array size to 512 in
modversion info entries. I therefore make it variably sized, with offset
to the next entry indicated by the initial "next" field.

In addition to supporting longer-than-56/60 byte symbols, this patch also
reduce the size for short symbols by getting rid of excessive 0 paddings.
There are still some zero paddings to ensure "next" and "crc" fields are
properly aligned.

This patch does have a tiny drawback that it makes ".mod.c" files generated
a bit less easy to read, as code like

	"\x08\x00\x00\x00\x78\x56\x34\x12"
	"symbol\0\0"

is generated as opposed to

	{ 0x12345678, "symbol" },

because the structure is now variable-length. But hopefully nobody reads
the generated file :)

Link: b8a94bfb33 ("kallsyms: increase maximum kernel symbol length to 512")
Link: https://github.com/Rust-for-Linux/linux/pull/379

Signed-off-by: Gary Guo <gary@garyguo.net>
(backported from https://lore.kernel.org/lkml/20230111161155.1349375-1-gary@garyguo.net/)
[ fix build error on s390x: always use a variable with TO_NATIVE() ]
[ add dummy NULL entry at the end of the modversion array ]
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
This commit is contained in:
Gary Guo
2023-01-11 16:11:51 +00:00
committed by Paolo Pisati
parent ad500f1b65
commit 0a4e704ad1
5 changed files with 48 additions and 31 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/powerpc/kernel/module_64.c
+3 -2
View File
@@ -347,12 +347,13 @@ static unsigned long get_got_size(const Elf64_Ehdr *hdr,
static void dedotify_versions(struct modversion_info *vers,
unsigned long size)
{
struct modversion_info *end;
struct modversion_info *end = (void *)vers + size;
for (end = (void *)vers + size; vers < end; vers++)
for (; vers < end && vers->next; vers = (void *)vers + vers->next) {
if (vers->name[0] == '.') {
memmove(vers->name, vers->name+1, strlen(vers->name));
}
}
}
/*
include/linux/module.h
+5 -3
View File
@@ -35,9 +35,11 @@
#define MODULE_NAME_LEN MAX_PARAM_PREFIX_LEN
struct modversion_info {
unsigned long crc;
char name[MODULE_NAME_LEN];
};
/* Offset of the next modversion entry in relation to this one. */
u32 next;
u32 crc;
char name[0];
} __packed;
struct module;
struct exception_table_entry;
kernel/module/version.c
+10 -12
View File
@@ -17,32 +17,30 @@ int check_version(const struct load_info *info,
{
Elf_Shdr *sechdrs = info->sechdrs;
unsigned int versindex = info->index.vers;
unsigned int i, num_versions;
struct modversion_info *versions;
struct modversion_info *versions, *end;
u32 crcval;
/* Exporting module didn't supply crcs? OK, we're already tainted. */
if (!crc)
return 1;
crcval = *crc;
/* No versions at all? modprobe --force does this. */
if (versindex == 0)
return try_to_force_load(mod, symname) == 0;
versions = (void *)sechdrs[versindex].sh_addr;
num_versions = sechdrs[versindex].sh_size
/ sizeof(struct modversion_info);
end = (void *)versions + sechdrs[versindex].sh_size;
for (i = 0; i < num_versions; i++) {
u32 crcval;
if (strcmp(versions[i].name, symname) != 0)
for (; versions < end && versions->next;
versions = (void *)versions + versions->next) {
if (strcmp(versions->name, symname) != 0)
continue;
crcval = *crc;
if (versions[i].crc == crcval)
if (versions->crc == crcval)
return 1;
pr_debug("Found checksum %X vs module %lX\n",
crcval, versions[i].crc);
pr_debug("Found checksum %X vs module %X\n",
crcval, versions->crc);
goto bad_version;
}
scripts/export_report.pl
+5 -4
View File
@@ -116,18 +116,19 @@ foreach my $thismod (@allcfiles) {
while ( <$module> ) {
chomp;
if ($state == 0) {
$state = 1 if ($_ =~ /static const struct modversion_info/);
$state = 1 if ($_ =~ /static const char ____versions/);
next;
}
if ($state == 1) {
$state = 2 if ($_ =~ /__attribute__\(\(section\("__versions"\)\)\)/);
$state = 2 if ($_ =~ /__used __section\("__versions"\)/);
next;
}
if ($state == 2) {
if ( $_ !~ /0x[0-9a-f]+,/ ) {
if ( $_ !~ /\\0"/ ) {
last if ($_ =~ /;/);
next;
}
my $sym = (split /([,"])/,)[4];
my $sym = (split /(["\\])/,)[2];
my ($module, $value, $symbol, $gpl) = @{$SYMBOL{$sym}};
$SYMBOL{ $sym } = [ $module, $value+1, $symbol, $gpl];
push(@{$MODULE{$thismod}} , $sym);
scripts/mod/modpost.c
+25 -10
View File
@@ -1900,13 +1900,17 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
static void add_versions(struct buffer *b, struct module *mod)
{
struct symbol *s;
unsigned int name_len;
unsigned int name_len_padded;
unsigned int tmp;
unsigned char *tmp_view = (unsigned char *)&tmp;
if (!modversions)
return;
buf_printf(b, "\n");
buf_printf(b, "static const struct modversion_info ____versions[]\n");
buf_printf(b, "__used __section(\"__versions\") = {\n");
buf_printf(b, "static const char ____versions[]\n");
buf_printf(b, "__used __section(\"__versions\") =\n");
list_for_each_entry(s, &mod->unresolved_symbols, list) {
if (!s->module)
@@ -1916,16 +1920,27 @@ static void add_versions(struct buffer *b, struct module *mod)
s->name, mod->name);
continue;
}
if (strlen(s->name) >= MODULE_NAME_LEN) {
error("too long symbol \"%s\" [%s.ko]\n",
s->name, mod->name);
break;
}
buf_printf(b, "\t{ %#8x, \"%s\" },\n",
s->crc, s->name);
name_len = strlen(s->name);
name_len_padded = (name_len + 1 + 3) & ~3;
/* Offset to next entry */
tmp = 8 + name_len_padded;
tmp = TO_NATIVE(tmp);
buf_printf(b, "\t\"\\x%02x\\x%02x\\x%02x\\x%02x",
tmp_view[0], tmp_view[1], tmp_view[2], tmp_view[3]);
tmp = TO_NATIVE(s->crc);
buf_printf(b, "\\x%02x\\x%02x\\x%02x\\x%02x\"\n",
tmp_view[0], tmp_view[1], tmp_view[2], tmp_view[3]);
buf_printf(b, "\t\"%s", s->name);
for (; name_len < name_len_padded; name_len++)
buf_printf(b, "\\0");
buf_printf(b, "\"\n");
}
buf_printf(b, "};\n");
/* Always end with a NULL entry */
buf_printf(b, "\t\"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\";\n");
}
static void add_depends(struct buffer *b, struct module *mod)