[PATCH v10 0/5] Extended MODVERSIONS Support

[PATCH v10 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 the module verification refactor patches [5]
that were split off of v5 (now in modules-next)
and DWARF-based versions [1].

[1] https://lore.kernel.org/all/20241121204220.2378181-20-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/
[5] https://lore.kernel.org/linux-modules/20241015231651.3851138-1-mmaurer@google.com/T/#t

Changes in v10:
- 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: 96ba0247d78ef4078e1de58b7e73715b93ee2c0b
change-id: 20241022-extended-modversions-a7b44dfbfff1
prerequisite-message-id: <20241121204220.2378181-20-samitolvanen@google.com>
prerequisite-patch-id: 43f1286f3e4b991fda2aa093539631a01fadf5fb
prerequisite-patch-id: 32a05b89083cfed15e5b877664b0c8138c40d09b
prerequisite-patch-id: e192e2a692c40d96cba919e3baae68c441ab25e4
prerequisite-patch-id: 50e884d28c720e90f201aae7801590d19736541b
prerequisite-patch-id: 4d6a826429c519b581d01215e1d9c7373fdfd8c6
prerequisite-patch-id: 0dcd84187b222adf52696dbcab303d683d087dd2
prerequisite-patch-id: 0abe8634eb844a85e8dc51c1cd3970cf96cc494a
prerequisite-patch-id: 5fabb630792f9304f200b5996314f3c2ae4c83ae
prerequisite-patch-id: ff82b9794147dc28504e46a0170cd269623e73bf
prerequisite-patch-id: a5cf20d27871bf63be64ac79cc81e5eb9d117b89
prerequisite-patch-id: 2a317596a3288f9b8e06d73df53737bbfafb1d16
prerequisite-patch-id: cac33b6e6672cf3f9f7f798a928ce7b147db271d
prerequisite-patch-id: 62664c468be8afff72a3edaf2c1bcd2f4936a1b2
prerequisite-patch-id: 5157d0421200858de3cc449bf39b3513efba3b24
prerequisite-patch-id: 5a190c60e140cdf33caf4f4da03186a2bd75a531
prerequisite-patch-id: 57d2fe708769154a6494fb1fece56911dea00687
prerequisite-patch-id: 25255d6bc70d3ba38e45fb6a2c13038df293bd9e
prerequisite-patch-id: 91c6131ab67a6f0fd8cf8bc95fa45144a868f095

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

[PATCH v10 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 5399c182b3cbed2dbeea0291f717f30358d8e7fc..5b5ce391d68529ecd778a93f1214e74136e53501 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.

-- 
2.47.0.371.ga323438b13-goog

[PATCH v10 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 e6b2427e5c190aacf7b9c5c1bb57fca39d311564..a31c617cd67d3d66b24d2fba34cbd5cc9c53ab78 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -208,6 +208,16 @@ 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 107393a8c48a5993dbe456702fec0652a967ee86..bd38f33fd41fbd98bce34f8924b2fb0ac04297ee 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -32,6 +32,8 @@ 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 */
@@ -1817,6 +1819,52 @@ 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
  **/
@@ -1840,9 +1888,14 @@ 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);
@@ -1972,6 +2025,7 @@ 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);
 	add_moddevtable(&buf, mod);
 	add_srcversion(&buf, mod);
@@ -2130,7 +2184,7 @@ 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;
@@ -2179,6 +2233,9 @@ int main(int argc, char **argv)
 		case 'd':
 			missing_namespace_deps = optarg;
 			break;
+		case 'x':
+			extended_modversions = true;
+			break;
 		default:
 			exit(1);
 		}

-- 
2.47.0.371.ga323438b13-goog

[PATCH v10 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 a31c617cd67d3d66b24d2fba34cbd5cc9c53ab78..35545bc1d96016f95fe4e95e8876159a4a4d616d 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -218,6 +218,21 @@ 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 bd38f33fd41fbd98bce34f8924b2fb0ac04297ee..ed52f9aa45a490bba706ffb2caa3e238e4697814 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -32,6 +32,8 @@ 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 */
@@ -1836,10 +1838,8 @@ 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);
@@ -1853,8 +1853,8 @@ 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.
 			 */
@@ -1872,7 +1872,7 @@ static void add_versions(struct buffer *b, struct module *mod)
 {
 	struct symbol *s;
 
-	if (!modversions)
+	if (!basic_modversions)
 		return;
 
 	buf_printf(b, "\n");
@@ -2184,7 +2184,7 @@ 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;
@@ -2233,6 +2233,9 @@ 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;

-- 
2.47.0.371.ga323438b13-goog

[PATCH v10 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..c32e3ed67cd26070f6929f6ad98c4308a1ab71f8 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 __kstrtab and
+	__kstrtabns respectively, 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
 ----------------------------
 

-- 
2.47.0.371.ga323438b13-goog

[PATCH v10 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 a20e6efd3f0fbdd7f0df2448854cc30734a0ee4f..2cfbefe0933ed129fdc1cca4121183e6285840d3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1956,7 +1956,8 @@ 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 9da9042fd62796ddb852f4bf7cf46d70f0b8ca97..397ce424a0509c2a1b4ebccd5d430b86b4ecbac6 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -316,10 +316,11 @@ $(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
 	$(call if_changed,exports)
@@ -388,11 +389,36 @@ ifneq ($(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))
@@ -404,13 +430,16 @@ 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)
 
@@ -422,6 +451,7 @@ $(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

-- 
2.47.0.371.ga323438b13-goog

Re: [PATCH v10 1/5] modules: Support extended MODVERSIONS info

[Michael Ellerman]

Matthew Maurer <mmaurer@google.com> writes:
> 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(-)

I already acked version 8, which AFAICS is identical to this version
(for this patch at least).

Not sure if you dropped my ack on purpose, but here have another one :)

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers

Re: [PATCH v10 1/5] modules: Support extended MODVERSIONS info

[Matthew Maurer]

>
> I already acked version 8, which AFAICS is identical to this version
> (for this patch at least).
>
> Not sure if you dropped my ack on purpose, but here have another one :)
>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
>
> cheers

It was not removed intentionally, thanks for the re-ack :)

Re: [PATCH v10 0/5] Extended MODVERSIONS Support

[Luis Chamberlain]

On Sat, Nov 23, 2024 at 02:42:14AM +0000, Matthew Maurer wrote:
> 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 the module verification refactor patches [5]
> that were split off of v5 (now in modules-next)
> and DWARF-based versions [1].

Thanks for doing all this.

Acked-by: Luis Chamberlain <mcgrof@kernel.org>

 Luis

Re: [PATCH v10 4/5] Documentation/kbuild: Document storage of symbol information

[Petr Pavlu]

On 11/23/24 03:42, Matthew Maurer wrote:
> 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..c32e3ed67cd26070f6929f6ad98c4308a1ab71f8 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 __kstrtab and
> +	__kstrtabns respectively, 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.

The second sentence should be that symbol names and namespaces of
exported symbols are both stored in the __ksymtab_strings section.

> +
> +	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
>  ----------------------------
>  
> 

-- 
Thanks,
Petr