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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
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;
}