[PATCH v4 01/16] module: Take const arg in validate_section_offset

[PATCH v4 01/16] module: Take const arg in validate_section_offset

[Matthew Maurer]

`validate_section_offset` doesn't modify the info passed in. Make this
clear by adjusting the type signature.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 49b9bca9de12..1a2dd52147ba 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1645,7 +1645,7 @@ bool __weak module_exit_section(const char *name)
 	return strstarts(name, ".exit");
 }
 
-static int validate_section_offset(struct load_info *info, Elf_Shdr *shdr)
+static int validate_section_offset(const struct load_info *info, Elf_Shdr *shdr)
 {
 #if defined(CONFIG_64BIT)
 	unsigned long long secend;
-- 
2.46.1.824.gd892dcdcdd-goog

Re: [PATCH v4 01/16] module: Take const arg in validate_section_offset

[Daniel Gomez]

On 9/24/2024 11:19 PM, Matthew Maurer wrote:
> `validate_section_offset` doesn't modify the info passed in. Make this
> clear by adjusting the type signature.
> 
> Signed-off-by: Matthew Maurer <mmaurer@google.com>
> ---
>   kernel/module/main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 49b9bca9de12..1a2dd52147ba 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1645,7 +1645,7 @@ bool __weak module_exit_section(const char *name)
>   	return strstarts(name, ".exit");
>   }
>   
> -static int validate_section_offset(struct load_info *info, Elf_Shdr *shdr)
> +static int validate_section_offset(const struct load_info *info, Elf_Shdr *shdr)
>   {
>   #if defined(CONFIG_64BIT)
>   	unsigned long long secend;


The cover letter is missing a From/Cc to the linux-modules list. So I 
was missing the context here. Looking at lore I found it here:

https://lore.kernel.org/asahi/20240924212024.540574-1-mmaurer@google.com/

Can you add linux-modules list in case there's a next revision?

Also, the cover letter is missing a full changelog other than a 
reference to the previous discussions and to the last changes.

Daniel

[PATCH v4 02/16] module: Factor out elf_validity_ehdr

[Matthew Maurer]

Factor out verification of the ELF header and document what is checked.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 70 +++++++++++++++++++++++++++++---------------
 1 file changed, 47 insertions(+), 23 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 1a2dd52147ba..59c977acfb44 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1664,6 +1664,50 @@ static int validate_section_offset(const struct load_info *info, Elf_Shdr *shdr)
 	return 0;
 }
 
+/**
+ * elf_validity_ehdr() - Checks an ELF header for module validity
+ * @info: Load info containing the ELF header to check
+ *
+ * Checks whether an ELF header could belong to a valid module. Checks:
+ *
+ * * ELF header is within the data the user provided
+ * * ELF magic is present
+ * * It is relocatable (not final linked, not core file, etc.)
+ * * The header's machine type matches what the architecture expects.
+ * * Optional arch-specific hook for other properties
+ *   - module_elf_check_arch() is currently only used by PPC to check
+ *   ELF ABI version, but may be used by others in the future.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_ehdr(const struct load_info *info)
+{
+	if (info->len < sizeof(*(info->hdr))) {
+		pr_err("Invalid ELF header len %lu\n", info->len);
+		return -ENOEXEC;
+	}
+	if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
+		pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
+		return -ENOEXEC;
+	}
+	if (info->hdr->e_type != ET_REL) {
+		pr_err("Invalid ELF header type: %u != %u\n",
+		       info->hdr->e_type, ET_REL);
+		return -ENOEXEC;
+	}
+	if (!elf_check_arch(info->hdr)) {
+		pr_err("Invalid architecture in ELF header: %u\n",
+		       info->hdr->e_machine);
+		return -ENOEXEC;
+	}
+	if (!module_elf_check_arch(info->hdr)) {
+		pr_err("Invalid module architecture in ELF header: %u\n",
+		       info->hdr->e_machine);
+		return -ENOEXEC;
+	}
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1693,30 +1737,10 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	unsigned int num_info_secs = 0, info_idx;
 	unsigned int num_sym_secs = 0, sym_idx;
 
-	if (info->len < sizeof(*(info->hdr))) {
-		pr_err("Invalid ELF header len %lu\n", info->len);
-		goto no_exec;
-	}
+	err = elf_validity_ehdr(info);
+	if (err < 0)
+		return err;
 
-	if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
-		pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
-		goto no_exec;
-	}
-	if (info->hdr->e_type != ET_REL) {
-		pr_err("Invalid ELF header type: %u != %u\n",
-		       info->hdr->e_type, ET_REL);
-		goto no_exec;
-	}
-	if (!elf_check_arch(info->hdr)) {
-		pr_err("Invalid architecture in ELF header: %u\n",
-		       info->hdr->e_machine);
-		goto no_exec;
-	}
-	if (!module_elf_check_arch(info->hdr)) {
-		pr_err("Invalid module architecture in ELF header: %u\n",
-		       info->hdr->e_machine);
-		goto no_exec;
-	}
 	if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
 		pr_err("Invalid ELF section header size\n");
 		goto no_exec;
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 03/16] module: Factor out elf_validity_cache_sechdrs

[Matthew Maurer]

Factor out and document the validation of section headers.

Because we now validate all section offsets and lengths before accessing
them, we can remove the ad-hoc checks.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 125 ++++++++++++++++++++++++++++---------------
 1 file changed, 82 insertions(+), 43 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 59c977acfb44..1f3a07ee59c6 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1708,6 +1708,87 @@ static int elf_validity_ehdr(const struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_sechdrs() - Cache section headers if valid
+ * @info: Load info to compute section headers from
+ *
+ * Checks:
+ *
+ * * ELF header is valid (see elf_validity_ehdr())
+ * * Section headers are the size we expect
+ * * Section array fits in the user provided data
+ * * Section index 0 is NULL
+ * * Section contents are inbounds
+ *
+ * Then updates @info with a &load_info->sechdrs pointer if valid.
+ *
+ * Return: %0 if valid, negative error code if validation failed.
+ */
+static int elf_validity_cache_sechdrs(struct load_info *info)
+{
+	Elf_Shdr *sechdrs;
+	Elf_Shdr *shdr;
+	int i;
+	int err;
+
+	err = elf_validity_ehdr(info);
+	if (err < 0)
+		return err;
+
+	if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
+		pr_err("Invalid ELF section header size\n");
+		return -ENOEXEC;
+	}
+
+	/*
+	 * e_shnum is 16 bits, and sizeof(Elf_Shdr) is
+	 * known and small. So e_shnum * sizeof(Elf_Shdr)
+	 * will not overflow unsigned long on any platform.
+	 */
+	if (info->hdr->e_shoff >= info->len
+	    || (info->hdr->e_shnum * sizeof(Elf_Shdr) >
+		info->len - info->hdr->e_shoff)) {
+		pr_err("Invalid ELF section header overflow\n");
+		return -ENOEXEC;
+	}
+
+	sechdrs = (void *)info->hdr + info->hdr->e_shoff;
+
+	/*
+	 * The code assumes that section 0 has a length of zero and
+	 * an addr of zero, so check for it.
+	 */
+	if (sechdrs[0].sh_type != SHT_NULL
+	    || sechdrs[0].sh_size != 0
+	    || sechdrs[0].sh_addr != 0) {
+		pr_err("ELF Spec violation: section 0 type(%d)!=SH_NULL or non-zero len or addr\n",
+		       sechdrs[0].sh_type);
+		return -ENOEXEC;
+	}
+
+	/* Validate contents are inbounds */
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		shdr = &sechdrs[i];
+		switch (shdr->sh_type) {
+		case SHT_NULL:
+		case SHT_NOBITS:
+			/* No contents, offset/size don't mean anything */
+			continue;
+		default:
+			err = validate_section_offset(info, shdr);
+			if (err < 0) {
+				pr_err("Invalid ELF section in module (section %u type %u)\n",
+				       i, shdr->sh_type);
+				return err;
+			}
+		}
+	}
+
+	info->sechdrs = sechdrs;
+
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1737,29 +1818,10 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	unsigned int num_info_secs = 0, info_idx;
 	unsigned int num_sym_secs = 0, sym_idx;
 
-	err = elf_validity_ehdr(info);
+	err = elf_validity_cache_sechdrs(info);
 	if (err < 0)
 		return err;
 
-	if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
-		pr_err("Invalid ELF section header size\n");
-		goto no_exec;
-	}
-
-	/*
-	 * e_shnum is 16 bits, and sizeof(Elf_Shdr) is
-	 * known and small. So e_shnum * sizeof(Elf_Shdr)
-	 * will not overflow unsigned long on any platform.
-	 */
-	if (info->hdr->e_shoff >= info->len
-	    || (info->hdr->e_shnum * sizeof(Elf_Shdr) >
-		info->len - info->hdr->e_shoff)) {
-		pr_err("Invalid ELF section header overflow\n");
-		goto no_exec;
-	}
-
-	info->sechdrs = (void *)info->hdr + info->hdr->e_shoff;
-
 	/*
 	 * Verify if the section name table index is valid.
 	 */
@@ -1772,11 +1834,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	}
 
 	strhdr = &info->sechdrs[info->hdr->e_shstrndx];
-	err = validate_section_offset(info, strhdr);
-	if (err < 0) {
-		pr_err("Invalid ELF section hdr(type %u)\n", strhdr->sh_type);
-		return err;
-	}
 
 	/*
 	 * The section name table must be NUL-terminated, as required
@@ -1793,18 +1850,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 		goto no_exec;
 	}
 
-	/*
-	 * The code assumes that section 0 has a length of zero and
-	 * an addr of zero, so check for it.
-	 */
-	if (info->sechdrs[0].sh_type != SHT_NULL
-	    || info->sechdrs[0].sh_size != 0
-	    || info->sechdrs[0].sh_addr != 0) {
-		pr_err("ELF Spec violation: section 0 type(%d)!=SH_NULL or non-zero len or addr\n",
-		       info->sechdrs[0].sh_type);
-		goto no_exec;
-	}
-
 	for (i = 1; i < info->hdr->e_shnum; i++) {
 		shdr = &info->sechdrs[i];
 		switch (shdr->sh_type) {
@@ -1823,12 +1868,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 			sym_idx = i;
 			fallthrough;
 		default:
-			err = validate_section_offset(info, shdr);
-			if (err < 0) {
-				pr_err("Invalid ELF section in module (section %u type %u)\n",
-					i, shdr->sh_type);
-				return err;
-			}
 			if (strcmp(info->secstrings + shdr->sh_name,
 				   ".gnu.linkonce.this_module") == 0) {
 				num_mod_secs++;
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 04/16] module: Factor out elf_validity_cache_secstrings

[Matthew Maurer]

Factor out the validation of section names.

There are two behavioral changes:

1. Previously, we did not validate non-SHF_ALLOC sections.
   This may have once been safe, as find_sec skips non-SHF_ALLOC
   sections, but find_any_sec, which will be used to load BTF if that is
   enabled, ignores the SHF_ALLOC flag. Since there's no need to support
   invalid section names, validate all of them, not just SHF_ALLOC
   sections.
2. Section names were validated *after* accessing them for the purposes
   of detecting ".modinfo" and ".gnu.linkonce.this_module". They are now
   checked prior to the access, which could avoid bad accesses with
   malformed modules.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 106 ++++++++++++++++++++++++++++---------------
 1 file changed, 69 insertions(+), 37 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 1f3a07ee59c6..6a9159afca02 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1789,6 +1789,71 @@ static int elf_validity_cache_sechdrs(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_secstrings() - Caches section names if valid
+ * @info: Load info to cache section names from. Must have valid sechdrs.
+ *
+ * Specifically checks:
+ *
+ * * Section name table index is inbounds of section headers
+ * * Section name table is not empty
+ * * Section name table is NUL terminated
+ * * All section name offsets are inbounds of the section
+ *
+ * Then updates @info with a &load_info->secstrings pointer if valid.
+ *
+ * Return: %0 if valid, negative error code if validation failed.
+ */
+static int elf_validity_cache_secstrings(struct load_info *info)
+{
+	Elf_Shdr *strhdr, *shdr;
+	char *secstrings;
+	int i;
+
+	/*
+	 * Verify if the section name table index is valid.
+	 */
+	if (info->hdr->e_shstrndx == SHN_UNDEF
+	    || info->hdr->e_shstrndx >= info->hdr->e_shnum) {
+		pr_err("Invalid ELF section name index: %d || e_shstrndx (%d) >= e_shnum (%d)\n",
+		       info->hdr->e_shstrndx, info->hdr->e_shstrndx,
+		       info->hdr->e_shnum);
+		return -ENOEXEC;
+	}
+
+	strhdr = &info->sechdrs[info->hdr->e_shstrndx];
+
+	/*
+	 * The section name table must be NUL-terminated, as required
+	 * by the spec. This makes strcmp and pr_* calls that access
+	 * strings in the section safe.
+	 */
+	secstrings = (void *)info->hdr + strhdr->sh_offset;
+	if (strhdr->sh_size == 0) {
+		pr_err("empty section name table\n");
+		return -ENOEXEC;
+	}
+	if (secstrings[strhdr->sh_size - 1] != '\0') {
+		pr_err("ELF Spec violation: section name table isn't null terminated\n");
+		return -ENOEXEC;
+	}
+
+	for (i = 0; i < info->hdr->e_shnum; i++) {
+		shdr = &info->sechdrs[i];
+		/* SHT_NULL means sh_name has an undefined value */
+		if (shdr->sh_type == SHT_NULL)
+			continue;
+		if (shdr->sh_name >= strhdr->sh_size) {
+			pr_err("Invalid ELF section name in module (section %u type %u)\n",
+			       i, shdr->sh_type);
+			return -ENOEXEC;
+		}
+	}
+
+	info->secstrings = secstrings;
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1812,7 +1877,7 @@ static int elf_validity_cache_sechdrs(struct load_info *info)
 static int elf_validity_cache_copy(struct load_info *info, int flags)
 {
 	unsigned int i;
-	Elf_Shdr *shdr, *strhdr;
+	Elf_Shdr *shdr;
 	int err;
 	unsigned int num_mod_secs = 0, mod_idx;
 	unsigned int num_info_secs = 0, info_idx;
@@ -1821,34 +1886,9 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	err = elf_validity_cache_sechdrs(info);
 	if (err < 0)
 		return err;
-
-	/*
-	 * Verify if the section name table index is valid.
-	 */
-	if (info->hdr->e_shstrndx == SHN_UNDEF
-	    || info->hdr->e_shstrndx >= info->hdr->e_shnum) {
-		pr_err("Invalid ELF section name index: %d || e_shstrndx (%d) >= e_shnum (%d)\n",
-		       info->hdr->e_shstrndx, info->hdr->e_shstrndx,
-		       info->hdr->e_shnum);
-		goto no_exec;
-	}
-
-	strhdr = &info->sechdrs[info->hdr->e_shstrndx];
-
-	/*
-	 * The section name table must be NUL-terminated, as required
-	 * by the spec. This makes strcmp and pr_* calls that access
-	 * strings in the section safe.
-	 */
-	info->secstrings = (void *)info->hdr + strhdr->sh_offset;
-	if (strhdr->sh_size == 0) {
-		pr_err("empty section name table\n");
-		goto no_exec;
-	}
-	if (info->secstrings[strhdr->sh_size - 1] != '\0') {
-		pr_err("ELF Spec violation: section name table isn't null terminated\n");
-		goto no_exec;
-	}
+	err = elf_validity_cache_secstrings(info);
+	if (err < 0)
+		return err;
 
 	for (i = 1; i < info->hdr->e_shnum; i++) {
 		shdr = &info->sechdrs[i];
@@ -1877,14 +1917,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 				num_info_secs++;
 				info_idx = i;
 			}
-
-			if (shdr->sh_flags & SHF_ALLOC) {
-				if (shdr->sh_name >= strhdr->sh_size) {
-					pr_err("Invalid ELF section name in module (section %u type %u)\n",
-					       i, shdr->sh_type);
-					return -ENOEXEC;
-				}
-			}
 			break;
 		}
 	}
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 05/16] module: Factor out elf_validity_cache_index_info

[Matthew Maurer]

Centralize .modinfo detection and property validation.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 82 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 68 insertions(+), 14 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 6a9159afca02..511d645ac577 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -195,6 +195,38 @@ static unsigned int find_sec(const struct load_info *info, const char *name)
 	return 0;
 }
 
+/**
+ * find_any_unique_sec() - Find a unique section index by name
+ * @info: Load info for the module to scan
+ * @name: Name of the section we're looking for
+ *
+ * Locates a unique section by name. Ignores SHF_ALLOC.
+ *
+ * Return: Section index if found uniquely, zero if absent, negative count
+ *         of total instances if multiple were found.
+ */
+static int find_any_unique_sec(const struct load_info *info, const char *name)
+{
+	unsigned int idx;
+	unsigned int count = 0;
+	int i;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		if (strcmp(info->secstrings + info->sechdrs[i].sh_name,
+			   name) == 0) {
+			count++;
+			idx = i;
+		}
+	}
+	if (count == 1) {
+		return idx;
+	} else if (count == 0) {
+		return 0;
+	} else {
+		return -count;
+	}
+}
+
 /* Find a module section, or NULL. */
 static void *section_addr(const struct load_info *info, const char *name)
 {
@@ -1854,6 +1886,39 @@ static int elf_validity_cache_secstrings(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index_info() - Validate and cache modinfo section
+ * @info: Load info to populate the modinfo index on.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated
+ *
+ * Checks that if there is a .modinfo section, it is unique.
+ * Then, it caches its index in &load_info->index.info.
+ * Finally, it tries to populate the name to improve error messages.
+ *
+ * Return: %0 if valid, %-ENOEXEC if multiple modinfo sections were found.
+ */
+static int elf_validity_cache_index_info(struct load_info *info)
+{
+	int info_idx;
+
+	info_idx = find_any_unique_sec(info, ".modinfo");
+
+	if (info_idx == 0)
+		/* Early return, no .modinfo */
+		return 0;
+
+	if (info_idx < 0) {
+		pr_err("Only one .modinfo section must exist.\n");
+		return -ENOEXEC;
+	}
+
+	info->index.info = info_idx;
+	/* Try to find a name early so we can log errors with a module name */
+	info->name = get_modinfo(info, "name");
+
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1880,13 +1945,15 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	Elf_Shdr *shdr;
 	int err;
 	unsigned int num_mod_secs = 0, mod_idx;
-	unsigned int num_info_secs = 0, info_idx;
 	unsigned int num_sym_secs = 0, sym_idx;
 
 	err = elf_validity_cache_sechdrs(info);
 	if (err < 0)
 		return err;
 	err = elf_validity_cache_secstrings(info);
+	if (err < 0)
+		return err;
+	err = elf_validity_cache_index_info(info);
 	if (err < 0)
 		return err;
 
@@ -1912,24 +1979,11 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 				   ".gnu.linkonce.this_module") == 0) {
 				num_mod_secs++;
 				mod_idx = i;
-			} else if (strcmp(info->secstrings + shdr->sh_name,
-				   ".modinfo") == 0) {
-				num_info_secs++;
-				info_idx = i;
 			}
 			break;
 		}
 	}
 
-	if (num_info_secs > 1) {
-		pr_err("Only one .modinfo section must exist.\n");
-		goto no_exec;
-	} else if (num_info_secs == 1) {
-		/* Try to find a name early so we can log errors with a module name */
-		info->index.info = info_idx;
-		info->name = get_modinfo(info, "name");
-	}
-
 	if (num_sym_secs != 1) {
 		pr_warn("%s: module has no symbols (stripped?)\n",
 			info->name ?: "(missing .modinfo section or name field)");
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 06/16] module: Factor out elf_validity_cache_index_mod

[Matthew Maurer]

Centralize .gnu.linkonce.this_module detection and property validation.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 129 ++++++++++++++++++++++---------------------
 1 file changed, 67 insertions(+), 62 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 511d645ac577..ec638187ffcf 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1919,6 +1919,68 @@ static int elf_validity_cache_index_info(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index_mod() - Validates and caches this_module section
+ * @info: Load info to cache this_module on.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated
+ *
+ * The ".gnu.linkonce.this_module" ELF section is special. It is what modpost
+ * uses to refer to __this_module and let's use rely on THIS_MODULE to point
+ * to &__this_module properly. The kernel's modpost declares it on each
+ * modules's *.mod.c file. If the struct module of the kernel changes a full
+ * kernel rebuild is required.
+ *
+ * We have a few expectations for this special section, this function
+ * validates all this for us:
+ *
+ * * The section has contents
+ * * The section is unique
+ * * We expect the kernel to always have to allocate it: SHF_ALLOC
+ * * The section size must match the kernel's run time's struct module
+ *   size
+ *
+ * If all checks pass, the index will be cached in &load_info->index.mod
+ *
+ * Return: %0 on validation success, %-ENOEXEC on failure
+ */
+static int elf_validity_cache_index_mod(struct load_info *info)
+{
+	Elf_Shdr *shdr;
+	int mod_idx;
+
+	mod_idx = find_any_unique_sec(info, ".gnu.linkonce.this_module");
+	if (mod_idx <= 0) {
+		pr_err("module %s: Exactly one .gnu.linkonce.this_module section must exist.\n",
+		       info->name ?: "(missing .modinfo section or name field)");
+		return -ENOEXEC;
+	}
+
+	shdr = &info->sechdrs[mod_idx];
+
+	if (shdr->sh_type == SHT_NOBITS) {
+		pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",
+		       info->name ?: "(missing .modinfo section or name field)");
+		return -ENOEXEC;
+	}
+
+	if (!(shdr->sh_flags & SHF_ALLOC)) {
+		pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",
+		       info->name ?: "(missing .modinfo section or name field)");
+		return -ENOEXEC;
+	}
+
+	if (shdr->sh_size != sizeof(struct module)) {
+		pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",
+		       info->name ?: "(missing .modinfo section or name field)");
+		return -ENOEXEC;
+	}
+
+	info->index.mod = mod_idx;
+
+	return 0;
+}
+
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1944,7 +2006,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	unsigned int i;
 	Elf_Shdr *shdr;
 	int err;
-	unsigned int num_mod_secs = 0, mod_idx;
 	unsigned int num_sym_secs = 0, sym_idx;
 
 	err = elf_validity_cache_sechdrs(info);
@@ -1954,16 +2015,15 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	if (err < 0)
 		return err;
 	err = elf_validity_cache_index_info(info);
+	if (err < 0)
+		return err;
+	err = elf_validity_cache_index_mod(info);
 	if (err < 0)
 		return err;
 
 	for (i = 1; i < info->hdr->e_shnum; i++) {
 		shdr = &info->sechdrs[i];
-		switch (shdr->sh_type) {
-		case SHT_NULL:
-		case SHT_NOBITS:
-			continue;
-		case SHT_SYMTAB:
+		if (shdr->sh_type == SHT_SYMTAB) {
 			if (shdr->sh_link == SHN_UNDEF
 			    || shdr->sh_link >= info->hdr->e_shnum) {
 				pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
@@ -1973,14 +2033,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 			}
 			num_sym_secs++;
 			sym_idx = i;
-			fallthrough;
-		default:
-			if (strcmp(info->secstrings + shdr->sh_name,
-				   ".gnu.linkonce.this_module") == 0) {
-				num_mod_secs++;
-				mod_idx = i;
-			}
-			break;
 		}
 	}
 
@@ -1996,55 +2048,8 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	info->index.str = shdr->sh_link;
 	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
 
-	/*
-	 * The ".gnu.linkonce.this_module" ELF section is special. It is
-	 * what modpost uses to refer to __this_module and let's use rely
-	 * on THIS_MODULE to point to &__this_module properly. The kernel's
-	 * modpost declares it on each modules's *.mod.c file. If the struct
-	 * module of the kernel changes a full kernel rebuild is required.
-	 *
-	 * We have a few expectaions for this special section, the following
-	 * code validates all this for us:
-	 *
-	 *   o Only one section must exist
-	 *   o We expect the kernel to always have to allocate it: SHF_ALLOC
-	 *   o The section size must match the kernel's run time's struct module
-	 *     size
-	 */
-	if (num_mod_secs != 1) {
-		pr_err("module %s: Only one .gnu.linkonce.this_module section must exist.\n",
-		       info->name ?: "(missing .modinfo section or name field)");
-		goto no_exec;
-	}
-
-	shdr = &info->sechdrs[mod_idx];
-
-	/*
-	 * This is already implied on the switch above, however let's be
-	 * pedantic about it.
-	 */
-	if (shdr->sh_type == SHT_NOBITS) {
-		pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",
-		       info->name ?: "(missing .modinfo section or name field)");
-		goto no_exec;
-	}
-
-	if (!(shdr->sh_flags & SHF_ALLOC)) {
-		pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",
-		       info->name ?: "(missing .modinfo section or name field)");
-		goto no_exec;
-	}
-
-	if (shdr->sh_size != sizeof(struct module)) {
-		pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",
-		       info->name ?: "(missing .modinfo section or name field)");
-		goto no_exec;
-	}
-
-	info->index.mod = mod_idx;
-
 	/* This is temporary: point mod into copy of data. */
-	info->mod = (void *)info->hdr + shdr->sh_offset;
+	info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset;
 
 	/*
 	 * If we didn't load the .modinfo 'name' field earlier, fall back to
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 07/16] module: Factor out elf_validity_cache_index_sym

[Matthew Maurer]

Centralize symbol table detection and property validation.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 73 ++++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 29 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index ec638187ffcf..6be58b0a6468 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1980,6 +1980,39 @@ static int elf_validity_cache_index_mod(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index_sym() - Validate and cache symtab index
+ * @info: Load info to cache symtab index in.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated.
+ *
+ * Checks that there is exactly one symbol table, then caches its index in
+ * &load_info->index.sym.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_cache_index_sym(struct load_info *info)
+{
+	unsigned int sym_idx;
+	unsigned int num_sym_secs = 0;
+	int i;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		if (info->sechdrs[i].sh_type == SHT_SYMTAB) {
+			num_sym_secs++;
+			sym_idx = i;
+		}
+	}
+
+	if (num_sym_secs != 1) {
+		pr_warn("%s: module has no symbols (stripped?)\n",
+			info->name ?: "(missing .modinfo section or name field)");
+		return -ENOEXEC;
+	}
+
+	info->index.sym = sym_idx;
+
+	return 0;
+}
 
 /*
  * Check userspace passed ELF module against our expectations, and cache
@@ -2003,10 +2036,8 @@ static int elf_validity_cache_index_mod(struct load_info *info)
  */
 static int elf_validity_cache_copy(struct load_info *info, int flags)
 {
-	unsigned int i;
-	Elf_Shdr *shdr;
 	int err;
-	unsigned int num_sym_secs = 0, sym_idx;
+	int str_idx;
 
 	err = elf_validity_cache_sechdrs(info);
 	if (err < 0)
@@ -2018,34 +2049,21 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	if (err < 0)
 		return err;
 	err = elf_validity_cache_index_mod(info);
+	if (err < 0)
+		return err;
+	err = elf_validity_cache_index_sym(info);
 	if (err < 0)
 		return err;
 
-	for (i = 1; i < info->hdr->e_shnum; i++) {
-		shdr = &info->sechdrs[i];
-		if (shdr->sh_type == SHT_SYMTAB) {
-			if (shdr->sh_link == SHN_UNDEF
-			    || shdr->sh_link >= info->hdr->e_shnum) {
-				pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
-				       shdr->sh_link, shdr->sh_link,
-				       info->hdr->e_shnum);
-				goto no_exec;
-			}
-			num_sym_secs++;
-			sym_idx = i;
-		}
-	}
-
-	if (num_sym_secs != 1) {
-		pr_warn("%s: module has no symbols (stripped?)\n",
-			info->name ?: "(missing .modinfo section or name field)");
-		goto no_exec;
+	str_idx = info->sechdrs[info->index.sym].sh_link;
+	if (str_idx == SHN_UNDEF || str_idx >= info->hdr->e_shnum) {
+		pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
+				str_idx, str_idx, info->hdr->e_shnum);
+		return -ENOEXEC;
 	}
 
-	/* Sets internal symbols and strings. */
-	info->index.sym = sym_idx;
-	shdr = &info->sechdrs[sym_idx];
-	info->index.str = shdr->sh_link;
+	/* Sets internal strings. */
+	info->index.str = str_idx;
 	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
 
 	/* This is temporary: point mod into copy of data. */
@@ -2066,9 +2084,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	info->index.pcpu = find_pcpusec(info);
 
 	return 0;
-
-no_exec:
-	return -ENOEXEC;
 }
 
 #define COPY_CHUNK_SIZE (16*PAGE_SIZE)
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 08/16] module: Factor out elf_validity_cache_index_str

[Matthew Maurer]

Pull out index validation for the symbol string section.

Note that this does not validate the *contents* of the string table,
only shape and presence of the section.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 6be58b0a6468..43140475aac0 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2014,6 +2014,31 @@ static int elf_validity_cache_index_sym(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index_str() - Validate and cache strtab index
+ * @info: Load info to cache strtab index in.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated.
+ *        Must have &load_info->index.sym populated.
+ *
+ * Looks at the symbol table's associated string table, makes sure it is
+ * in-bounds, and caches it.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_cache_index_str(struct load_info *info)
+{
+	unsigned int str_idx = info->sechdrs[info->index.sym].sh_link;
+
+	if (str_idx == SHN_UNDEF || str_idx >= info->hdr->e_shnum) {
+		pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
+		       str_idx, str_idx, info->hdr->e_shnum);
+		return -ENOEXEC;
+	}
+
+	info->index.str = str_idx;
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -2037,7 +2062,6 @@ static int elf_validity_cache_index_sym(struct load_info *info)
 static int elf_validity_cache_copy(struct load_info *info, int flags)
 {
 	int err;
-	int str_idx;
 
 	err = elf_validity_cache_sechdrs(info);
 	if (err < 0)
@@ -2054,16 +2078,11 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	err = elf_validity_cache_index_sym(info);
 	if (err < 0)
 		return err;
-
-	str_idx = info->sechdrs[info->index.sym].sh_link;
-	if (str_idx == SHN_UNDEF || str_idx >= info->hdr->e_shnum) {
-		pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
-				str_idx, str_idx, info->hdr->e_shnum);
-		return -ENOEXEC;
-	}
+	err = elf_validity_cache_index_str(info);
+	if (err < 0)
+		return err;
 
 	/* Sets internal strings. */
-	info->index.str = str_idx;
 	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
 
 	/* This is temporary: point mod into copy of data. */
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 09/16] module: Group section index calculations together

[Matthew Maurer]

Group all the index detection together to make the parent function
easier to read.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 68 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 51 insertions(+), 17 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 43140475aac0..e04a228c694a 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2039,6 +2039,56 @@ static int elf_validity_cache_index_str(struct load_info *info)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_index() - Resolve, validate, cache section indices
+ * @info:  Load info to read from and update.
+ *         &load_info->sechdrs and &load_info->secstrings must be populated.
+ * @flags: Load flags, relevant to suppress version loading, see
+ *         uapi/linux/module.h
+ *
+ * Populates &load_info->index, validating as it goes.
+ * See child functions for per-field validation:
+ *
+ * * elf_validity_cache_index_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.
+ *
+ * If CONFIG_SMP is enabled, load the percpu section by name with no
+ * validation.
+ *
+ * Return: 0 on success, negative error code if an index failed validation.
+ */
+static int elf_validity_cache_index(struct load_info *info, int flags)
+{
+	int err;
+
+	err = elf_validity_cache_index_info(info);
+	if (err < 0)
+		return err;
+	err = elf_validity_cache_index_mod(info);
+	if (err < 0)
+		return err;
+	err = elf_validity_cache_index_sym(info);
+	if (err < 0)
+		return err;
+	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");
+
+	info->index.pcpu = find_pcpusec(info);
+
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -2069,16 +2119,7 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	err = elf_validity_cache_secstrings(info);
 	if (err < 0)
 		return err;
-	err = elf_validity_cache_index_info(info);
-	if (err < 0)
-		return err;
-	err = elf_validity_cache_index_mod(info);
-	if (err < 0)
-		return err;
-	err = elf_validity_cache_index_sym(info);
-	if (err < 0)
-		return err;
-	err = elf_validity_cache_index_str(info);
+	err = elf_validity_cache_index(info, flags);
 	if (err < 0)
 		return err;
 
@@ -2095,13 +2136,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	if (!info->name)
 		info->name = info->mod->name;
 
-	if (flags & MODULE_INIT_IGNORE_MODVERSIONS)
-		info->index.vers = 0; /* Pretend no __versions section! */
-	else
-		info->index.vers = find_sec(info, "__versions");
-
-	info->index.pcpu = find_pcpusec(info);
-
 	return 0;
 }
 
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 10/16] module: Factor out elf_validity_cache_strtab

[Matthew Maurer]

This patch only moves the existing strtab population to a function.
Validation comes in a following patch, this is split out to make the new
validation checks more clearly separated.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index e04a228c694a..c082d5d41a8d 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2089,6 +2089,23 @@ static int elf_validity_cache_index(struct load_info *info, int flags)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_strtab() - Cache symbol string table
+ * @info: Load info to read from and update.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated.
+ *        Must have &load_info->index populated.
+ *
+ * Return: 0 on success, negative error code if a check failed.
+ */
+static int elf_validity_cache_strtab(struct load_info *info)
+{
+	Elf_Shdr *str_shdr = &info->sechdrs[info->index.str];
+	char *strtab = (char *)info->hdr + str_shdr->sh_offset;
+
+	info->strtab = strtab;
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -2122,9 +2139,9 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	err = elf_validity_cache_index(info, flags);
 	if (err < 0)
 		return err;
-
-	/* Sets internal strings. */
-	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
+	err = elf_validity_cache_strtab(info);
+	if (err < 0)
+		return err;
 
 	/* This is temporary: point mod into copy of data. */
 	info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset;
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 11/16] module: Additional validation in elf_validity_cache_strtab

[Matthew Maurer]

Validate properties of the strtab that are depended on elsewhere, but
were previously unchecked:
* String table nonempty (offset 0 is valid)
* String table has a leading NUL (offset 0 corresponds to "")
* String table is NUL terminated (strfoo functions won't run out of the
  table while reading).
* All symbols names are inbounds of the string table.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/main.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index c082d5d41a8d..b40b632f00a6 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2090,17 +2090,53 @@ static int elf_validity_cache_index(struct load_info *info, int flags)
 }
 
 /**
- * elf_validity_cache_strtab() - Cache symbol string table
+ * elf_validity_cache_strtab() - Validate and cache symbol string table
  * @info: Load info to read from and update.
  *        Must have &load_info->sechdrs and &load_info->secstrings populated.
  *        Must have &load_info->index populated.
  *
+ * Checks:
+ *
+ * * The string table is not empty.
+ * * The string table starts and ends with NUL (required by ELF spec).
+ * * Every &Elf_Sym->st_name offset in the symbol table is inbounds of the
+ *   string table.
+ *
+ * And caches the pointer as &load_info->strtab in @info.
+ *
  * Return: 0 on success, negative error code if a check failed.
  */
 static int elf_validity_cache_strtab(struct load_info *info)
 {
 	Elf_Shdr *str_shdr = &info->sechdrs[info->index.str];
+	Elf_Shdr *sym_shdr = &info->sechdrs[info->index.sym];
 	char *strtab = (char *)info->hdr + str_shdr->sh_offset;
+	Elf_Sym *syms = (void *)info->hdr + sym_shdr->sh_offset;
+	int i;
+
+	if (str_shdr->sh_size == 0) {
+		pr_err("empty symbol string table\n");
+		return -ENOEXEC;
+	}
+	if (strtab[0] != '\0') {
+		pr_err("symbol string table missing leading NUL\n");
+		return -ENOEXEC;
+	}
+	if (strtab[str_shdr->sh_size - 1] != '\0') {
+		pr_err("symbol string table isn't NUL terminated\n");
+		return -ENOEXEC;
+	}
+
+	/*
+	 * Now that we know strtab is correctly structured, check symbol
+	 * starts are inbounds before they're used later.
+	 */
+	for (i = 0; i < sym_shdr->sh_size / sizeof(*syms); i++) {
+		if (syms[i].st_name >= str_shdr->sh_size) {
+			pr_err("symbol name out of bounds in string table");
+			return -ENOEXEC;
+		}
+	}
 
 	info->strtab = strtab;
 	return 0;
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 12/16] module: Reformat struct for code style

[Matthew Maurer]

Using commas to declare struct members makes adding new members to this
struct not as nice with patch management.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/internal.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 2ebece8a789f..daef2be83902 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -80,7 +80,12 @@ struct load_info {
 	unsigned int used_pages;
 #endif
 	struct {
-		unsigned int sym, str, mod, vers, info, pcpu;
+		unsigned int sym;
+		unsigned int str;
+		unsigned int mod;
+		unsigned int vers;
+		unsigned int info;
+		unsigned int pcpu;
 	} index;
 };
 
-- 
2.46.1.824.gd892dcdcdd-goog

[PATCH v4 14/16] 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.

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         | 43 +++++++++++++++
 4 files changed, 160 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index e9bab599d0c2..92e5a0db06d3 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -355,6 +355,24 @@ static void dedotify_versions(struct modversion_info *vers,
 		}
 }
 
+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++) {
+		if (last == '\0')
+			/* Skip one leading dot */
+			if (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).
@@ -424,10 +442,12 @@ 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 daef2be83902..59959c21b205 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 b40b632f00a6..9a9feca344f8 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2039,6 +2039,82 @@ 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.
@@ -2053,9 +2129,7 @@ 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.
@@ -2078,11 +2152,9 @@ 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);
 
@@ -2293,6 +2365,10 @@ 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 53f43ac5a73e..02d8340bdb57 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 +104,32 @@ 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;
+
+	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.
-- 
2.46.1.824.gd892dcdcdd-goog

Re: [PATCH v4 14/16] modules: Support extended MODVERSIONS info

[Sami Tolvanen]

Hi Matt,

On Tue, Sep 24, 2024 at 09:19:56PM +0000, Matthew Maurer wrote:
> +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++) {
> +		if (last == '\0')
> +			/* Skip one leading dot */
> +			if (str_seq[in] == '.')
> +				in++;

Thanks for addressing Michael's comment, this looks correct to me.

Nit: might be cleaner in a single if statement though:

	/* Skip one leading dot */
	if (last == '\0' && str_seq[in] == '.')
		in++;

> +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;
> +
> +	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);
> +}

This looks unchanged from v3, so I think my comment from there
still applies:

https://lore.kernel.org/lkml/CABCJKufJK0WO92wnW09VTLqZk0ODxhuKQG=HbKE-va0urJU1Vg@mail.gmail.com/

Sami

Re: [PATCH v4 14/16] modules: Support extended MODVERSIONS info

[Matthew Maurer]

Thanks for the catch. I've sent up v5 to include that fix. I've also
added a changelog and made sure the patches make it to linux-modules@
as Daniel suggested.


On Wed, Sep 25, 2024 at 4:00 PM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Hi Matt,
>
> On Tue, Sep 24, 2024 at 09:19:56PM +0000, Matthew Maurer wrote:
> > +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++) {
> > +             if (last == '\0')
> > +                     /* Skip one leading dot */
> > +                     if (str_seq[in] == '.')
> > +                             in++;
>
> Thanks for addressing Michael's comment, this looks correct to me.
>
> Nit: might be cleaner in a single if statement though:
>
>         /* Skip one leading dot */
>         if (last == '\0' && str_seq[in] == '.')
>                 in++;
>
> > +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;
> > +
> > +     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);
> > +}
>
> This looks unchanged from v3, so I think my comment from there
> still applies:
>
> https://lore.kernel.org/lkml/CABCJKufJK0WO92wnW09VTLqZk0ODxhuKQG=HbKE-va0urJU1Vg@mail.gmail.com/
>
> Sami