[1/2] module: get symbol crc back to unsigned

Commit Message

Masahiro Yamada Dec. 28, 2024, 3:45 p.m. UTC

Commit 71810db27c1c ("modversions: treat symbol CRCs as 32 bit
quantities") changed the CRC fields to s32 because the __kcrctab and
__kcrctab_gpl sections contained relative references to the actual
CRC values stored in the .rodata section when CONFIG_MODULE_REL_CRCS=y.

Commit 7b4537199a4a ("kbuild: link symbol CRCs at final link, removing
CONFIG_MODULE_REL_CRCS") removed this complexity. Now, the __kcrctab
and __kcrctab_gpl sections directly contain the CRC values in all cases.

The genksyms tool outputs unsigned 32-bit CRC values, so u32 is preferred
over s32.

No functional changes are intended.

Regardless of this change, the CRC value is assigned to the u32 variable,
'crcval' before the comparison, as seen in kernel/module/version.c:

    crcval = *crc;

Signed-off-by: Masahiro Yamada <[e-mail]>
---

 include/linux/module.h   |  4 ++--
 kernel/module/internal.h | 10 +++++-----
 kernel/module/main.c     |  2 +-
 kernel/module/version.c  |  2 +-
 4 files changed, 9 insertions(+), 9 deletions(-)

Comments

Masahiro Yamada Dec. 28, 2024, 4:12 p.m. UTC | #1

On Sun, Dec 29, 2024 at 12:46 AM Masahiro Yamada <[e-mail]> wrote:
>
> Commit 71810db27c1c ("modversions: treat symbol CRCs as 32 bit
> quantities") changed the CRC fields to s32 because the __kcrctab and
> __kcrctab_gpl sections contained relative references to the actual
> CRC values stored in the .rodata section when CONFIG_MODULE_REL_CRCS=y.
>
> Commit 7b4537199a4a ("kbuild: link symbol CRCs at final link, removing
> CONFIG_MODULE_REL_CRCS") removed this complexity. Now, the __kcrctab
> and __kcrctab_gpl sections directly contain the CRC values in all cases.
>
> The genksyms tool outputs unsigned 32-bit CRC values, so u32 is preferred
> over s32.
>
> No functional changes are intended.
>
> Regardless of this change, the CRC value is assigned to the u32 variable,
> 'crcval' before the comparison, as seen in kernel/module/version.c:
>
>     crcval = *crc;


[Just in case for confused reviewers]

It was previously mandatory (but now optional) in order to avoid sign
extension because the following line previously compared 'unsigned long'
and 's32':

    if (versions[i].crc == crcval)
            return 1;

versions[i].crc is still 'unsigned long' for backward compatibility.

Patch

diff --git a/include/linux/module.h b/include/linux/module.h
index 94acbacdcdf1..903ef8fe4c04 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -430,7 +430,7 @@  struct module {
 
 	/* Exported symbols */
 	const struct kernel_symbol *syms;
-	const s32 *crcs;
+	const u32 *crcs;
 	unsigned int num_syms;
 
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
@@ -448,7 +448,7 @@  struct module {
 	/* GPL-only exported symbols. */
 	unsigned int num_gpl_syms;
 	const struct kernel_symbol *gpl_syms;
-	const s32 *gpl_crcs;
+	const u32 *gpl_crcs;
 	bool using_gplonly_symbols;
 
 #ifdef CONFIG_MODULE_SIG
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index daef2be83902..f10dc3ea7ff8 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -55,8 +55,8 @@  extern const struct kernel_symbol __start___ksymtab[];
 extern const struct kernel_symbol __stop___ksymtab[];
 extern const struct kernel_symbol __start___ksymtab_gpl[];
 extern const struct kernel_symbol __stop___ksymtab_gpl[];
-extern const s32 __start___kcrctab[];
-extern const s32 __start___kcrctab_gpl[];
+extern const u32 __start___kcrctab[];
+extern const u32 __start___kcrctab_gpl[];
 
 struct load_info {
 	const char *name;
@@ -102,7 +102,7 @@  struct find_symbol_arg {
 
 	/* Output */
 	struct module *owner;
-	const s32 *crc;
+	const u32 *crc;
 	const struct kernel_symbol *sym;
 	enum mod_license license;
 };
@@ -384,7 +384,7 @@  static inline void init_param_lock(struct module *mod) { }
 
 #ifdef CONFIG_MODVERSIONS
 int check_version(const struct load_info *info,
-		  const char *symname, struct module *mod, const s32 *crc);
+		  const char *symname, struct module *mod, const u32 *crc);
 void module_layout(struct module *mod, struct modversion_info *ver, struct kernel_param *kp,
 		   struct kernel_symbol *ks, struct tracepoint * const *tp);
 int check_modstruct_version(const struct load_info *info, struct module *mod);
@@ -393,7 +393,7 @@  int same_magic(const char *amagic, const char *bmagic, bool has_crcs);
 static inline int check_version(const struct load_info *info,
 				const char *symname,
 				struct module *mod,
-				const s32 *crc)
+				const u32 *crc)
 {
 	return 1;
 }
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 5399c182b3cb..e58bff88b8d6 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -86,7 +86,7 @@  struct mod_tree_root mod_tree __cacheline_aligned = {
 
 struct symsearch {
 	const struct kernel_symbol *start, *stop;
-	const s32 *crcs;
+	const u32 *crcs;
 	enum mod_license license;
 };
 
diff --git a/kernel/module/version.c b/kernel/module/version.c
index 53f43ac5a73e..4e5731d403af 100644
--- a/kernel/module/version.c
+++ b/kernel/module/version.c
@@ -13,7 +13,7 @@ 
 int check_version(const struct load_info *info,
 		  const char *symname,
 			 struct module *mod,
-			 const s32 *crc)
+			 const u32 *crc)
 {
 	Elf_Shdr *sechdrs = info->sechdrs;
 	unsigned int versindex = info->index.vers;