[PATCH v11 0/5] Extended MODVERSIONS Support

[PATCH v11 0/5] Extended MODVERSIONS Support

[Matthew Maurer]

This patch series is intended for use alongside the Implement DWARF
modversions series [1] to enable RUST and MODVERSIONS at the same
time.

Elsewhere, we've seen a desire for long symbol name support for LTO
symbol names [2], and the previous series came up [3] as a possible
solution rather than hashing, which some have objected [4] to.

This series adds a MODVERSIONS format which uses a section per column.
This avoids userspace tools breaking if we need to make a similar change
to the format in the future - we would do so by adding a new section,
rather than editing the struct definition. In the new format, the name
section is formatted as a concatenated sequence of NUL-terminated
strings, which allows for arbitrary length names.

Emitting the extended format is guarded by CONFIG_EXTENDED_MODVERSIONS,
but the kernel always knows how to validate both the original and
extended formats.

Emitting the existing format is now guarded by CONFIG_BASIC_MODVERSIONS,
but it is enabled by default when MODVERSIONS is enabled and must be
explicitly disabled by the user.

Disabling CONFIG_BASIC_MODVERSIONS may cause some userspace tools to be
unable to retrieve CRCs until they are patched to understand the new
location. Even with CONFIG_BASIC_MODVERSIONS enabled, those tools will
be unable to read the CRCs for long symbols until they are updated to
read the new format. This is not expected to interfere with normal
operation, as the primary use for CRCs embedded in the module is
load-time verification by the kernel. Recording and monitoring of CRCs
is typically done through Module.symvers.

Selecting RUST and MODVERSIONS is now possible if GENDWARFKSYMS is
selected, and will implicitly select EXTENDED_MODVERSIONS.

This series depends upon DWARF-based versions [1].

[1] https://lore.kernel.org/lkml/20241219210736.2990838-20-samitolvanen@google.com/	
[2] https://lore.kernel.org/lkml/20240605032120.3179157-1-song@kernel.org/
[3] https://lore.kernel.org/lkml/ZoxbEEsK40ASi1cY@bombadil.infradead.org/
[4] https://lore.kernel.org/lkml/0b2697fd-7ab4-469f-83a6-ec9ebc701ba0@suse.com/

Changes in v11:
- Fixed documentation about where strings are stored per Petr's
  suggestion.
- Rebased on to the latest version of Sami's series on linux-next

v10: https://lore.kernel.org/r/20241123-extended-modversions-v10-0-0fa754ffdee3@google.com
- Fixed accidental selects / default confusion in previous patch
- Re-ran tests (check for section presence in Y/Y, Y/N, N/Y, N/N, check
  all module kinds load)

v9: https://lore.kernel.org/r/20241123-extended-modversions-v9-0-bc0403f054bf@google.com
- Rebased onto the latest version of Sami's series, on top of linux-next
- Added BASIC_MODVERSIONS to allow using *only* EXTENDED_MODVERSIONS
- Documented where symbol data is stored and format limitations

v8: https://lore.kernel.org/r/20241030-extended-modversions-v8-0-93acdef62ce8@google.com
- Rebased onto latest version of Sami's series, on top of v6.12-rc5
- Pass --stable when KBUILD_GENDWARFKSYMS_STABLE is set.
- Flipped MODVERSIONS/GENDWARFKSYMS order in deps for CONFIG_RUST
- Picked up trailers

v7: https://lore.kernel.org/r/20241023-extended-modversions-v7-0-339787b43373@google.com
- Fix modpost to detect EXTENDED_MODVERSIONS based on a flag
- Drop patches to fix export_report.pl
- Switch from conditional compilation in .mod.c to conditional emission
  in modpost
- Factored extended modversion emission into its own function
- Allow RUST + MODVERSIONS if GENDWARFKSYMS is enabled by selecting
  EXTENDED_MODVERSIONS

v6: https://lore.kernel.org/lkml/20241015231925.3854230-1-mmaurer@google.com/
- Splits verification refactor Luis requested out to a separate change
- Clarifies commits around export_report.pl repairs
- Add CONFIG_EXTENDED_MODVERSIONS to control whether extended
  information is included in the module, per Luis's request.

v5: https://lore.kernel.org/all/20240925233854.90072-1-mmaurer@google.com/
- Addresses Sami's comments from v3 that I missed in v4 (missing early
  return, extra parens)

v4: https://lore.kernel.org/asahi/20240924212024.540574-1-mmaurer@google.com/
- Fix incorrect dot munging in PPC

v3: https://lore.kernel.org/lkml/87le0w2hop.fsf@mail.lhotse/T/
- Split up the module verification refactor into smaller patches, per
  Greg K-H's suggestion.

v2: https://lore.kernel.org/all/20231118025748.2778044-1-mmaurer@google.com/
- Add loading/verification refactor before modifying, per Luis's request

v1: https://lore.kernel.org/rust-for-linux/20231115185858.2110875-1-mmaurer@google.com/

--
2.47.0.rc1.288.g06298d1525-goog

---
Matthew Maurer (4):
      modules: Support extended MODVERSIONS info
      modpost: Produce extended MODVERSIONS information
      modules: Allow extended modversions without basic MODVERSIONS
      Documentation/kbuild: Document storage of symbol information

Sami Tolvanen (1):
      rust: Use gendwarfksyms + extended modversions for CONFIG_MODVERSIONS

 Documentation/kbuild/modules.rst | 20 +++++++++
 arch/powerpc/kernel/module_64.c  | 24 ++++++++++-
 init/Kconfig                     |  3 +-
 kernel/module/Kconfig            | 25 +++++++++++
 kernel/module/internal.h         | 11 +++++
 kernel/module/main.c             | 92 ++++++++++++++++++++++++++++++++++++----
 kernel/module/version.c          | 45 ++++++++++++++++++++
 rust/Makefile                    | 34 ++++++++++++++-
 scripts/Makefile.modpost         |  2 +
 scripts/mod/modpost.c            | 70 +++++++++++++++++++++++++++---
 10 files changed, 308 insertions(+), 18 deletions(-)
---
base-commit: b2c5bc987160cbc8478b982991f34f53189af909
change-id: 20241022-extended-modversions-a7b44dfbfff1
prerequisite-message-id: <20241219210736.2990838-20-samitolvanen@google.com>
prerequisite-patch-id: 8a6a82b2f1858ee1483f41a1aa72c8cb030559ac
prerequisite-patch-id: 5b22bc2e7f592e464d5d1dd4341efa2fb2afb9d0
prerequisite-patch-id: 220585cf1a8d66ec722cf1d6ec474af6dc3b6a02
prerequisite-patch-id: 8ae7cb66d809f902968f81354706edeb99a3d3fa
prerequisite-patch-id: 4d6a826429c519b581d01215e1d9c7373fdfd8c6
prerequisite-patch-id: 0dcd84187b222adf52696dbcab303d683d087dd2
prerequisite-patch-id: 0abe8634eb844a85e8dc51c1cd3970cf96cc494a
prerequisite-patch-id: 5fabb630792f9304f200b5996314f3c2ae4c83ae
prerequisite-patch-id: 2772364d4b2132c9ede451f320162fc40c6f3d09
prerequisite-patch-id: a5cf20d27871bf63be64ac79cc81e5eb9d117b89
prerequisite-patch-id: 930230702709fe769b171a8ae94955e5d1de13ea
prerequisite-patch-id: b43c0bc886a312e3b14be04a8fdad25badf4d834
prerequisite-patch-id: 839b0c4859bdc8447d67bfe4b09f762140e747e7
prerequisite-patch-id: 3c55d1e58a1d7aebfc3ea85ef5497a7262022040
prerequisite-patch-id: 5a190c60e140cdf33caf4f4da03186a2bd75a531
prerequisite-patch-id: 57d2fe708769154a6494fb1fece56911dea00687
prerequisite-patch-id: 7e046331b05c61a87e1adc923b763b68a580cd03
prerequisite-patch-id: 91c6131ab67a6f0fd8cf8bc95fa45144a868f095

Best regards,
-- 
Matthew Maurer <mmaurer@google.com>

[PATCH v11 1/5] modules: Support extended MODVERSIONS info

[Matthew Maurer]

Adds a new format for MODVERSIONS which stores each field in a separate
ELF section. This initially adds support for variable length names, but
could later be used to add additional fields to MODVERSIONS in a
backwards compatible way if needed. Any new fields will be ignored by
old user tooling, unlike the current format where user tooling cannot
tolerate adjustments to the format (for example making the name field
longer).

Since PPC munges its version records to strip leading dots, we reproduce
the munging for the new format. Other architectures do not appear to
have architecture-specific usage of this information.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 arch/powerpc/kernel/module_64.c | 24 ++++++++++-
 kernel/module/internal.h        | 11 +++++
 kernel/module/main.c            | 92 +++++++++++++++++++++++++++++++++++++----
 kernel/module/version.c         | 45 ++++++++++++++++++++
 4 files changed, 162 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 45dac7b46aa3cdcb2058a2320b88c0d67e5586b3..34a5aec4908fba3b91a02e914264cb525918942a 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -369,6 +369,24 @@ static void dedotify_versions(struct modversion_info *vers,
 		}
 }
 
+/* Same as normal versions, remove a leading dot if present. */
+static void dedotify_ext_version_names(char *str_seq, unsigned long size)
+{
+	unsigned long out = 0;
+	unsigned long in;
+	char last = '\0';
+
+	for (in = 0; in < size; in++) {
+		/* Skip one leading dot */
+		if (last == '\0' && str_seq[in] == '.')
+			in++;
+		last = str_seq[in];
+		str_seq[out++] = last;
+	}
+	/* Zero the trailing portion of the names table for robustness */
+	memset(&str_seq[out], 0, size - out);
+}
+
 /*
  * Undefined symbols which refer to .funcname, hack to funcname. Make .TOC.
  * seem to be defined (value set later).
@@ -438,10 +456,12 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
 			me->arch.toc_section = i;
 			if (sechdrs[i].sh_addralign < 8)
 				sechdrs[i].sh_addralign = 8;
-		}
-		else if (strcmp(secstrings+sechdrs[i].sh_name,"__versions")==0)
+		} else if (strcmp(secstrings + sechdrs[i].sh_name, "__versions") == 0)
 			dedotify_versions((void *)hdr + sechdrs[i].sh_offset,
 					  sechdrs[i].sh_size);
+		else if (strcmp(secstrings + sechdrs[i].sh_name, "__version_ext_names") == 0)
+			dedotify_ext_version_names((void *)hdr + sechdrs[i].sh_offset,
+						   sechdrs[i].sh_size);
 
 		if (sechdrs[i].sh_type == SHT_SYMTAB)
 			dedotify((void *)hdr + sechdrs[i].sh_offset,
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index daef2be8390222c22220e2f168baa8d35ad531b9..59959c21b205bf91c0073260885743098c4022cf 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -86,6 +86,8 @@ struct load_info {
 		unsigned int vers;
 		unsigned int info;
 		unsigned int pcpu;
+		unsigned int vers_ext_crc;
+		unsigned int vers_ext_name;
 	} index;
 };
 
@@ -389,6 +391,15 @@ void module_layout(struct module *mod, struct modversion_info *ver, struct kerne
 		   struct kernel_symbol *ks, struct tracepoint * const *tp);
 int check_modstruct_version(const struct load_info *info, struct module *mod);
 int same_magic(const char *amagic, const char *bmagic, bool has_crcs);
+struct modversion_info_ext {
+	size_t remaining;
+	const s32 *crc;
+	const char *name;
+};
+void modversion_ext_start(const struct load_info *info, struct modversion_info_ext *ver);
+void modversion_ext_advance(struct modversion_info_ext *ver);
+#define for_each_modversion_info_ext(ver, info) \
+	for (modversion_ext_start(info, &ver); ver.remaining > 0; modversion_ext_advance(&ver))
 #else /* !CONFIG_MODVERSIONS */
 static inline int check_version(const struct load_info *info,
 				const char *symname,
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 878191c65efc629f14659712cd2b7ee972a6f73d..b5c052cb05715609c1d7a59c1b9efd2dc9b1d668 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2073,6 +2073,82 @@ static int elf_validity_cache_index_str(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index_versions() - Validate and cache version indices
+ * @info:  Load info to cache version indices in.
+ *         Must have &load_info->sechdrs and &load_info->secstrings populated.
+ * @flags: Load flags, relevant to suppress version loading, see
+ *         uapi/linux/module.h
+ *
+ * If we're ignoring modversions based on @flags, zero all version indices
+ * and return validity. Othewrise check:
+ *
+ * * If "__version_ext_crcs" is present, "__version_ext_names" is present
+ * * There is a name present for every crc
+ *
+ * Then populate:
+ *
+ * * &load_info->index.vers
+ * * &load_info->index.vers_ext_crc
+ * * &load_info->index.vers_ext_names
+ *
+ * if present.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_cache_index_versions(struct load_info *info, int flags)
+{
+	unsigned int vers_ext_crc;
+	unsigned int vers_ext_name;
+	size_t crc_count;
+	size_t remaining_len;
+	size_t name_size;
+	char *name;
+
+	/* If modversions were suppressed, pretend we didn't find any */
+	if (flags & MODULE_INIT_IGNORE_MODVERSIONS) {
+		info->index.vers = 0;
+		info->index.vers_ext_crc = 0;
+		info->index.vers_ext_name = 0;
+		return 0;
+	}
+
+	vers_ext_crc = find_sec(info, "__version_ext_crcs");
+	vers_ext_name = find_sec(info, "__version_ext_names");
+
+	/* If we have one field, we must have the other */
+	if (!!vers_ext_crc != !!vers_ext_name) {
+		pr_err("extended version crc+name presence does not match");
+		return -ENOEXEC;
+	}
+
+	/*
+	 * If we have extended version information, we should have the same
+	 * number of entries in every section.
+	 */
+	if (vers_ext_crc) {
+		crc_count = info->sechdrs[vers_ext_crc].sh_size / sizeof(s32);
+		name = (void *)info->hdr +
+			info->sechdrs[vers_ext_name].sh_offset;
+		remaining_len = info->sechdrs[vers_ext_name].sh_size;
+
+		while (crc_count--) {
+			name_size = strnlen(name, remaining_len) + 1;
+			if (name_size > remaining_len) {
+				pr_err("more extended version crcs than names");
+				return -ENOEXEC;
+			}
+			remaining_len -= name_size;
+			name += name_size;
+		}
+	}
+
+	info->index.vers = find_sec(info, "__versions");
+	info->index.vers_ext_crc = vers_ext_crc;
+	info->index.vers_ext_name = vers_ext_name;
+	return 0;
+}
+
 /**
  * elf_validity_cache_index() - Resolve, validate, cache section indices
  * @info:  Load info to read from and update.
@@ -2087,9 +2163,7 @@ static int elf_validity_cache_index_str(struct load_info *info)
  * * elf_validity_cache_index_mod()
  * * elf_validity_cache_index_sym()
  * * elf_validity_cache_index_str()
- *
- * If versioning is not suppressed via flags, load the version index from
- * a section called "__versions" with no validation.
+ * * elf_validity_cache_index_versions()
  *
  * If CONFIG_SMP is enabled, load the percpu section by name with no
  * validation.
@@ -2112,11 +2186,9 @@ static int elf_validity_cache_index(struct load_info *info, int flags)
 	err = elf_validity_cache_index_str(info);
 	if (err < 0)
 		return err;
-
-	if (flags & MODULE_INIT_IGNORE_MODVERSIONS)
-		info->index.vers = 0; /* Pretend no __versions section! */
-	else
-		info->index.vers = find_sec(info, "__versions");
+	err = elf_validity_cache_index_versions(info, flags);
+	if (err < 0)
+		return err;
 
 	info->index.pcpu = find_pcpusec(info);
 
@@ -2327,6 +2399,10 @@ static int rewrite_section_headers(struct load_info *info, int flags)
 
 	/* Track but don't keep modinfo and version sections. */
 	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
+	info->sechdrs[info->index.vers_ext_crc].sh_flags &=
+		~(unsigned long)SHF_ALLOC;
+	info->sechdrs[info->index.vers_ext_name].sh_flags &=
+		~(unsigned long)SHF_ALLOC;
 	info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
 
 	return 0;
diff --git a/kernel/module/version.c b/kernel/module/version.c
index 53f43ac5a73e9d537a9e95ff97728a51fad0e797..c246d40879706d4f413fa7ea9bbe2264ea1b2aa8 100644
--- a/kernel/module/version.c
+++ b/kernel/module/version.c
@@ -19,11 +19,28 @@ int check_version(const struct load_info *info,
 	unsigned int versindex = info->index.vers;
 	unsigned int i, num_versions;
 	struct modversion_info *versions;
+	struct modversion_info_ext version_ext;
 
 	/* Exporting module didn't supply crcs?  OK, we're already tainted. */
 	if (!crc)
 		return 1;
 
+	/* If we have extended version info, rely on it */
+	if (info->index.vers_ext_crc) {
+		for_each_modversion_info_ext(version_ext, info) {
+			if (strcmp(version_ext.name, symname) != 0)
+				continue;
+			if (*version_ext.crc == *crc)
+				return 1;
+			pr_debug("Found checksum %X vs module %X\n",
+				 *crc, *version_ext.crc);
+			goto bad_version;
+		}
+		pr_warn_once("%s: no extended symbol version for %s\n",
+			     info->name, symname);
+		return 1;
+	}
+
 	/* No versions at all?  modprobe --force does this. */
 	if (versindex == 0)
 		return try_to_force_load(mod, symname) == 0;
@@ -87,6 +104,34 @@ int same_magic(const char *amagic, const char *bmagic,
 	return strcmp(amagic, bmagic) == 0;
 }
 
+void modversion_ext_start(const struct load_info *info,
+			  struct modversion_info_ext *start)
+{
+	unsigned int crc_idx = info->index.vers_ext_crc;
+	unsigned int name_idx = info->index.vers_ext_name;
+	Elf_Shdr *sechdrs = info->sechdrs;
+
+	/*
+	 * Both of these fields are needed for this to be useful
+	 * Any future fields should be initialized to NULL if absent.
+	 */
+	if (crc_idx == 0 || name_idx == 0) {
+		start->remaining = 0;
+		return;
+	}
+
+	start->crc = (const s32 *)sechdrs[crc_idx].sh_addr;
+	start->name = (const char *)sechdrs[name_idx].sh_addr;
+	start->remaining = sechdrs[crc_idx].sh_size / sizeof(*start->crc);
+}
+
+void modversion_ext_advance(struct modversion_info_ext *vers)
+{
+	vers->remaining--;
+	vers->crc++;
+	vers->name += strlen(vers->name) + 1;
+}
+
 /*
  * Generate the signature for all relevant module structures here.
  * If these change, we don't want to try to parse the module.

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v11 2/5] modpost: Produce extended MODVERSIONS information

[Matthew Maurer]

Generate both the existing modversions format and the new extended one
when running modpost. Presence of this metadata in the final .ko is
guarded by CONFIG_EXTENDED_MODVERSIONS.

We no longer generate an error on long symbols in modpost if
CONFIG_EXTENDED_MODVERSIONS is set, as they can now be appropriately
encoded in the extended section. These symbols will be skipped in the
previous encoding. An error will still be generated if
CONFIG_EXTENDED_MODVERSIONS is not set.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/Kconfig    | 10 ++++++++
 scripts/Makefile.modpost |  1 +
 scripts/mod/modpost.c    | 65 +++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 72 insertions(+), 4 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index d443fc504ffca0d1001f880ec496ab1f21fe979e..9568b629a03ce8289d3f3597eefc66fc96445720 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -207,6 +207,16 @@ config ASM_MODVERSIONS
 	  assembly. This can be enabled only when the target architecture
 	  supports it.
 
+config EXTENDED_MODVERSIONS
+	bool "Extended Module Versioning Support"
+	depends on MODVERSIONS
+	help
+	  This enables extended MODVERSIONs support, allowing long symbol
+	  names to be versioned.
+
+	  The most likely reason you would enable this is to enable Rust
+	  support. If unsure, say N.
+
 config MODULE_SRCVERSION_ALL
 	bool "Source checksum for all modules"
 	help
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index ab0e94ea62496e11dbaa3ffc289ce546862795ca..40426fc6350985780c0092beb49c6cc29b9eff62 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -43,6 +43,7 @@ MODPOST = $(objtree)/scripts/mod/modpost
 modpost-args =										\
 	$(if $(CONFIG_MODULES),-M)							\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
+	$(if $(CONFIG_EXTENDED_MODVERSIONS),-x)						\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
 	$(if $(KBUILD_MODPOST_WARN),-w)							\
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index fb787a5715f5e8b37713162979ca45355770dc73..c58f08681fc1e37929333ba3a3e0989c4db5a79d 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -33,6 +33,8 @@ static bool module_enabled;
 static bool modversions;
 /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
 static bool all_versions;
+/* Is CONFIG_EXTENDED_MODVERSIONS set? */
+static bool extended_modversions;
 /* If we are modposting external module set to 1 */
 static bool external_module;
 /* Only warn about unresolved symbols */
@@ -1804,6 +1806,52 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
 	}
 }
 
+/**
+ * Record CRCs for unresolved symbols, supporting long names
+ */
+static void add_extended_versions(struct buffer *b, struct module *mod)
+{
+	struct symbol *s;
+
+	if (!extended_modversions)
+		return;
+
+	buf_printf(b, "\n");
+	buf_printf(b, "static const s32 ____version_ext_crcs[]\n");
+	buf_printf(b, "__used __section(\"__version_ext_crcs\") = {\n");
+	list_for_each_entry(s, &mod->unresolved_symbols, list) {
+		if (!s->module)
+			continue;
+		if (!s->crc_valid) {
+			/*
+			 * We already warned on this when producing the legacy
+			 * modversions table.
+			 */
+			continue;
+		}
+		buf_printf(b, "\t%#8x,\n", s->crc);
+	}
+	buf_printf(b, "};\n");
+
+	buf_printf(b, "static const char ____version_ext_names[]\n");
+	buf_printf(b, "__used __section(\"__version_ext_names\") =\n");
+	list_for_each_entry(s, &mod->unresolved_symbols, list) {
+		if (!s->module)
+			continue;
+		if (!s->crc_valid) {
+			/*
+			 * We already warned on this when producing the legacy
+			 * modversions table.
+			 * We need to skip its name too, as the indexes in
+			 * both tables need to align.
+			 */
+			continue;
+		}
+		buf_printf(b, "\t\"%s\\0\"\n", s->name);
+	}
+	buf_printf(b, ";\n");
+}
+
 /**
  * Record CRCs for unresolved symbols
  **/
@@ -1827,9 +1875,14 @@ static void add_versions(struct buffer *b, struct module *mod)
 			continue;
 		}
 		if (strlen(s->name) >= MODULE_NAME_LEN) {
-			error("too long symbol \"%s\" [%s.ko]\n",
-			      s->name, mod->name);
-			break;
+			if (extended_modversions)
+				/* this symbol will only be in the extended info */
+				continue;
+			else {
+				error("too long symbol \"%s\" [%s.ko]\n",
+				      s->name, mod->name);
+				break;
+			}
 		}
 		buf_printf(b, "\t{ %#8x, \"%s\" },\n",
 			   s->crc, s->name);
@@ -1960,6 +2013,7 @@ static void write_mod_c_file(struct module *mod)
 	add_header(&buf, mod);
 	add_exported_symbols(&buf, mod);
 	add_versions(&buf, mod);
+	add_extended_versions(&buf, mod);
 	add_depends(&buf, mod);
 
 	buf_printf(&buf, "\n");
@@ -2125,7 +2179,7 @@ int main(int argc, char **argv)
 	LIST_HEAD(dump_lists);
 	struct dump_list *dl, *dl2;
 
-	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:")) != -1) {
+	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:x")) != -1) {
 		switch (opt) {
 		case 'e':
 			external_module = true;
@@ -2174,6 +2228,9 @@ int main(int argc, char **argv)
 		case 'd':
 			missing_namespace_deps = optarg;
 			break;
+		case 'x':
+			extended_modversions = true;
+			break;
 		default:
 			exit(1);
 		}

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v11 3/5] modules: Allow extended modversions without basic MODVERSIONS

[Matthew Maurer]

If you know that your kernel modules will only ever be loaded by a newer
kernel, you can disable BASIC_MODVERSIONS to save space. This also
allows easy creation of test modules to seee how tooling will respond to
modules that only have the new format.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/Kconfig    | 15 +++++++++++++++
 scripts/Makefile.modpost |  1 +
 scripts/mod/modpost.c    | 19 +++++++++++--------
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 9568b629a03ce8289d3f3597eefc66fc96445720..5f701391ab12c7d1b3ca496c9b3443c5a76a8745 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -217,6 +217,21 @@ config EXTENDED_MODVERSIONS
 	  The most likely reason you would enable this is to enable Rust
 	  support. If unsure, say N.
 
+config BASIC_MODVERSIONS
+	bool "Basic Module Versioning Support"
+	depends on MODVERSIONS
+	default MODVERSIONS
+	help
+	  This enables basic MODVERSIONS support, allowing older tools or
+	  kernels to potentially load modules.
+
+	  Disabling this may cause older `modprobe` or `kmod` to be unable
+	  to read MODVERSIONS information from built modules. With this
+	  disabled, older kernels may treat this module as unversioned.
+
+	  This is enabled by default when MODVERSIONS are enabled.
+	  If unsure, say Y.
+
 config MODULE_SRCVERSION_ALL
 	bool "Source checksum for all modules"
 	help
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 40426fc6350985780c0092beb49c6cc29b9eff62..d7d45067d08b94a82451d66a64eae29b6826e139 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -43,6 +43,7 @@ MODPOST = $(objtree)/scripts/mod/modpost
 modpost-args =										\
 	$(if $(CONFIG_MODULES),-M)							\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
+	$(if $(CONFIG_BASIC_MODVERSIONS),-b)						\
 	$(if $(CONFIG_EXTENDED_MODVERSIONS),-x)						\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index c58f08681fc1e37929333ba3a3e0989c4db5a79d..d13d10bf534a4c15fa76fffb2a1dc9832bd0e95a 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -33,6 +33,8 @@ static bool module_enabled;
 static bool modversions;
 /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
 static bool all_versions;
+/* Is CONFIG_BASIC_MODVERSIONS set? */
+static bool basic_modversions;
 /* Is CONFIG_EXTENDED_MODVERSIONS set? */
 static bool extended_modversions;
 /* If we are modposting external module set to 1 */
@@ -1823,10 +1825,8 @@ static void add_extended_versions(struct buffer *b, struct module *mod)
 		if (!s->module)
 			continue;
 		if (!s->crc_valid) {
-			/*
-			 * We already warned on this when producing the legacy
-			 * modversions table.
-			 */
+			warn("\"%s\" [%s.ko] has no CRC!\n",
+				s->name, mod->name);
 			continue;
 		}
 		buf_printf(b, "\t%#8x,\n", s->crc);
@@ -1840,8 +1840,8 @@ static void add_extended_versions(struct buffer *b, struct module *mod)
 			continue;
 		if (!s->crc_valid) {
 			/*
-			 * We already warned on this when producing the legacy
-			 * modversions table.
+			 * We already warned on this when producing the crc
+			 * table.
 			 * We need to skip its name too, as the indexes in
 			 * both tables need to align.
 			 */
@@ -1859,7 +1859,7 @@ static void add_versions(struct buffer *b, struct module *mod)
 {
 	struct symbol *s;
 
-	if (!modversions)
+	if (!basic_modversions)
 		return;
 
 	buf_printf(b, "\n");
@@ -2179,7 +2179,7 @@ int main(int argc, char **argv)
 	LIST_HEAD(dump_lists);
 	struct dump_list *dl, *dl2;
 
-	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:x")) != -1) {
+	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:xb")) != -1) {
 		switch (opt) {
 		case 'e':
 			external_module = true;
@@ -2228,6 +2228,9 @@ int main(int argc, char **argv)
 		case 'd':
 			missing_namespace_deps = optarg;
 			break;
+		case 'b':
+			basic_modversions = true;
+			break;
 		case 'x':
 			extended_modversions = true;
 			break;

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v11 4/5] Documentation/kbuild: Document storage of symbol information

[Matthew Maurer]

Document where exported and imported symbols are kept, format options,
and limitations.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 Documentation/kbuild/modules.rst | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
index 101de236cd0c9abe1f5684d80063ff3f9a7fc673..a42f00d8cb90ff6ee44677c1278287ef25a84c89 100644
--- a/Documentation/kbuild/modules.rst
+++ b/Documentation/kbuild/modules.rst
@@ -423,6 +423,26 @@ Symbols From the Kernel (vmlinux + modules)
 	1) It lists all exported symbols from vmlinux and all modules.
 	2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
 
+Version Information Formats
+---------------------------
+
+	Exported symbols have information stored in __ksymtab or __ksymtab_gpl
+	sections. Symbol names and namespaces are stored in __ksymtab_strings,
+	using a format similar to the string table used for ELF. If
+	CONFIG_MODVERSIONS is enabled, the CRCs corresponding to exported
+	symbols will be added to the __kcrctab or __kcrctab_gpl.
+
+	If CONFIG_BASIC_MODVERSIONS is enabled (default with
+	CONFIG_MODVERSIONS), imported symbols will have their symbol name and
+	CRC stored in the __versions section of the importing module. This
+	mode only supports symbols of length up to 64 bytes.
+
+	If CONFIG_EXTENDED_MODVERSIONS is enabled (required to enable both
+	CONFIG_MODVERSIONS and CONFIG_RUST at the same time), imported symbols
+	will have their symbol name recorded in the __version_ext_names
+	section as a series of concatenated, null-terminated strings. CRCs for
+	these symbols will be recorded in the __version_ext_crcs section.
+
 Symbols and External Modules
 ----------------------------
 

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v11 5/5] rust: Use gendwarfksyms + extended modversions for CONFIG_MODVERSIONS

[Matthew Maurer]

From: Sami Tolvanen <samitolvanen@google.com>

Previously, two things stopped Rust from using MODVERSIONS:
1. Rust symbols are occasionally too long to be represented in the
   original versions table
2. Rust types cannot be properly hashed by the existing genksyms
   approach because:
	* Looking up type definitions in Rust is more complex than C
	* Type layout is potentially dependent on the compiler in Rust,
	  not just the source type declaration.

CONFIG_EXTENDED_MODVERSIONS addresses the first point, and
CONFIG_GENDWARFKSYMS the second. If Rust wants to use MODVERSIONS, allow
it to do so by selecting both features.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Co-developed-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 init/Kconfig  |  3 ++-
 rust/Makefile | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index c1f9eb3d5f2e892e977ba1425599502dc830f552..b60acfd9431e0ac2bf401ecb6523b5104ad31150 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1959,7 +1959,8 @@ config RUST
 	bool "Rust support"
 	depends on HAVE_RUST
 	depends on RUST_IS_AVAILABLE
-	depends on !MODVERSIONS
+	select EXTENDED_MODVERSIONS if MODVERSIONS
+	depends on !MODVERSIONS || GENDWARFKSYMS
 	depends on !GCC_PLUGIN_RANDSTRUCT
 	depends on !RANDSTRUCT
 	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
diff --git a/rust/Makefile b/rust/Makefile
index a40a3936126d603836e0ec9b42a1285916b60e45..80f970ad81f7989afe5ff2b5f633f50feb7f6006 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -329,10 +329,11 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ;
 $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
 	$(call if_changed_dep,bindgen)
 
+rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ { printf $(2),$(3) }'
+
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
-	$(NM) -p --defined-only $< \
-		| awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
+	$(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3) > $@
 
 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 	$(call if_changed,exports)
@@ -401,11 +402,36 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 		__ashlti3 __lshrti3
 endif
 
+ifdef CONFIG_MODVERSIONS
+cmd_gendwarfksyms = $(if $(skip_gendwarfksyms),, \
+	$(call rust_exports,$@,"%s\n",$$3) | \
+	scripts/gendwarfksyms/gendwarfksyms \
+		$(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable) \
+		$(if $(KBUILD_SYMTYPES), --symtypes $(@:.o=.symtypes),) \
+		$@ >> $(dot-target).cmd)
+endif
+
 define rule_rustc_library
 	$(call cmd_and_fixdep,rustc_library)
 	$(call cmd,gen_objtooldep)
+	$(call cmd,gendwarfksyms)
 endef
 
+define rule_rust_cc_library
+	$(call if_changed_rule,cc_o_c)
+	$(call cmd,force_checksrc)
+	$(call cmd,gendwarfksyms)
+endef
+
+# helpers.o uses the same export mechanism as Rust libraries, so ensure symbol
+# versions are calculated for the helpers too.
+$(obj)/helpers/helpers.o: $(src)/helpers/helpers.c $(recordmcount_source) FORCE
+	+$(call if_changed_rule,rust_cc_library)
+
+# Disable symbol versioning for exports.o to avoid conflicts with the actual
+# symbol versions generated from Rust objects.
+$(obj)/exports.o: private skip_gendwarfksyms = 1
+
 $(obj)/core.o: private skip_clippy = 1
 $(obj)/core.o: private skip_flags = -Wunreachable_pub
 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
@@ -417,13 +443,16 @@ ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
 $(obj)/core.o: scripts/target.json
 endif
 
+$(obj)/compiler_builtins.o: private skip_gendwarfksyms = 1
 $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
 $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
+$(obj)/build_error.o: private skip_gendwarfksyms = 1
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
+$(obj)/ffi.o: private skip_gendwarfksyms = 1
 $(obj)/ffi.o: $(src)/ffi.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
@@ -435,6 +464,7 @@ $(obj)/bindings.o: $(src)/bindings/lib.rs \
 	+$(call if_changed_rule,rustc_library)
 
 $(obj)/uapi.o: private rustc_target_flags = --extern ffi
+$(obj)/uapi.o: private skip_gendwarfksyms = 1
 $(obj)/uapi.o: $(src)/uapi/lib.rs \
     $(obj)/ffi.o \
     $(obj)/uapi/uapi_generated.rs FORCE

-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH v11 3/5] modules: Allow extended modversions without basic MODVERSIONS

[Masahiro Yamada]

On Tue, Dec 24, 2024 at 5:13 AM Matthew Maurer <mmaurer@google.com> wrote:
>
> If you know that your kernel modules will only ever be loaded by a newer
> kernel, you can disable BASIC_MODVERSIONS to save space. This also
> allows easy creation of test modules to seee how tooling will respond to


seee -> see


> modules that only have the new format.
>
> Signed-off-by: Matthew Maurer <mmaurer@google.com>
> ---
>  kernel/module/Kconfig    | 15 +++++++++++++++
>  scripts/Makefile.modpost |  1 +
>  scripts/mod/modpost.c    | 19 +++++++++++--------
>  3 files changed, 27 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index 9568b629a03ce8289d3f3597eefc66fc96445720..5f701391ab12c7d1b3ca496c9b3443c5a76a8745 100644
> --- a/kernel/module/Kconfig
> +++ b/kernel/module/Kconfig
> @@ -217,6 +217,21 @@ config EXTENDED_MODVERSIONS
>           The most likely reason you would enable this is to enable Rust
>           support. If unsure, say N.
>
> +config BASIC_MODVERSIONS
> +       bool "Basic Module Versioning Support"
> +       depends on MODVERSIONS
> +       default MODVERSIONS

Nit:

            default y

is simpler.


--
Best Regards

Masahiro Yamada

Re: [PATCH v11 2/5] modpost: Produce extended MODVERSIONS information

[Masahiro Yamada]

On Tue, Dec 24, 2024 at 5:13 AM Matthew Maurer <mmaurer@google.com> wrote:
>
> Generate both the existing modversions format and the new extended one
> when running modpost. Presence of this metadata in the final .ko is
> guarded by CONFIG_EXTENDED_MODVERSIONS.
>
> We no longer generate an error on long symbols in modpost if
> CONFIG_EXTENDED_MODVERSIONS is set, as they can now be appropriately
> encoded in the extended section. These symbols will be skipped in the
> previous encoding. An error will still be generated if
> CONFIG_EXTENDED_MODVERSIONS is not set.
>
> Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Matthew Maurer <mmaurer@google.com>
> ---
>  kernel/module/Kconfig    | 10 ++++++++
>  scripts/Makefile.modpost |  1 +
>  scripts/mod/modpost.c    | 65 +++++++++++++++++++++++++++++++++++++++++++++---
>  3 files changed, 72 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index d443fc504ffca0d1001f880ec496ab1f21fe979e..9568b629a03ce8289d3f3597eefc66fc96445720 100644
> --- a/kernel/module/Kconfig
> +++ b/kernel/module/Kconfig
> @@ -207,6 +207,16 @@ config ASM_MODVERSIONS
>           assembly. This can be enabled only when the target architecture
>           supports it.
>
> +config EXTENDED_MODVERSIONS
> +       bool "Extended Module Versioning Support"
> +       depends on MODVERSIONS
> +       help
> +         This enables extended MODVERSIONs support, allowing long symbol
> +         names to be versioned.
> +
> +         The most likely reason you would enable this is to enable Rust
> +         support. If unsure, say N.
> +
>  config MODULE_SRCVERSION_ALL
>         bool "Source checksum for all modules"
>         help
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index ab0e94ea62496e11dbaa3ffc289ce546862795ca..40426fc6350985780c0092beb49c6cc29b9eff62 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -43,6 +43,7 @@ MODPOST = $(objtree)/scripts/mod/modpost
>  modpost-args =                                                                         \
>         $(if $(CONFIG_MODULES),-M)                                                      \
>         $(if $(CONFIG_MODVERSIONS),-m)                                                  \
> +       $(if $(CONFIG_EXTENDED_MODVERSIONS),-x)                                         \
>         $(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)                                        \
>         $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)                                  \
>         $(if $(KBUILD_MODPOST_WARN),-w)                                                 \
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index fb787a5715f5e8b37713162979ca45355770dc73..c58f08681fc1e37929333ba3a3e0989c4db5a79d 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -33,6 +33,8 @@ static bool module_enabled;
>  static bool modversions;
>  /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
>  static bool all_versions;
> +/* Is CONFIG_EXTENDED_MODVERSIONS set? */
> +static bool extended_modversions;
>  /* If we are modposting external module set to 1 */
>  static bool external_module;
>  /* Only warn about unresolved symbols */
> @@ -1804,6 +1806,52 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
>         }
>  }
>
> +/**
> + * Record CRCs for unresolved symbols, supporting long names
> + */
> +static void add_extended_versions(struct buffer *b, struct module *mod)
> +{
> +       struct symbol *s;
> +
> +       if (!extended_modversions)
> +               return;
> +
> +       buf_printf(b, "\n");
> +       buf_printf(b, "static const s32 ____version_ext_crcs[]\n");

In general, 's32' (i.e. signed) and the '%x' printf-format (i.e. unsigned)
are an odd combination. I know why you are mixing up these.

Previously, we had a reason to use 's32' because the 'crc' field may
contain a negative address offset.

After commit 7b4537199a4a, there is no more reason
for keeping this weirdness.

I will apply the following first.

https://lore.kernel.org/linux-kbuild/20241228154603.2234284-2-masahiroy@kernel.org/T/#u

Then, you can change 's32' to 'u32' in this series.




> +       buf_printf(b, "__used __section(\"__version_ext_crcs\") = {\n");
> +       list_for_each_entry(s, &mod->unresolved_symbols, list) {
> +               if (!s->module)
> +                       continue;
> +               if (!s->crc_valid) {
> +                       /*
> +                        * We already warned on this when producing the legacy
> +                        * modversions table.
> +                        */
> +                       continue;

Personally, I tend to avoid a noise change because you will change this comment
to warn() in the next commit.
It is up to you.



> +               }
> +               buf_printf(b, "\t%#8x,\n", s->crc);


This is also a copy-paste of the existing code.

I like to have zero-padding for better alignment.

Please follow this format:
https://lore.kernel.org/linux-kbuild/20241228154603.2234284-2-masahiroy@kernel.org/T/#mc46376f41c0313c660990e92ed37689432f325c7




> +       }
> +       buf_printf(b, "};\n");
> +
> +       buf_printf(b, "static const char ____version_ext_names[]\n");
> +       buf_printf(b, "__used __section(\"__version_ext_names\") =\n");
> +       list_for_each_entry(s, &mod->unresolved_symbols, list) {
> +               if (!s->module)
> +                       continue;
> +               if (!s->crc_valid) {
> +                       /*
> +                        * We already warned on this when producing the legacy
> +                        * modversions table.
> +                        * We need to skip its name too, as the indexes in
> +                        * both tables need to align.
> +                        */
> +                       continue;
> +               }

Unnecessary braces.

Reason:
https://github.com/torvalds/linux/blob/v6.12/Documentation/process/coding-style.rst?plain=1#L197


> +               buf_printf(b, "\t\"%s\\0\"\n", s->name);
> +       }
> +       buf_printf(b, ";\n");
> +}
> +
>  /**
>   * Record CRCs for unresolved symbols
>   **/
> @@ -1827,9 +1875,14 @@ static void add_versions(struct buffer *b, struct module *mod)
>                         continue;
>                 }
>                 if (strlen(s->name) >= MODULE_NAME_LEN) {
> -                       error("too long symbol \"%s\" [%s.ko]\n",
> -                             s->name, mod->name);
> -                       break;
> +                       if (extended_modversions)
> +                               /* this symbol will only be in the extended info */
> +                               continue;

You need braces here.

Reason:
https://github.com/torvalds/linux/blob/v6.12/Documentation/process/coding-style.rst?plain=1#L213




--
Best Regards
Masahiro Yamada