linux-kernel - [PATCH 05/12] module: Factor out elf_validity_cache_index

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Message-ID: <20241015231651.3851138-6-mmaurer@google.com>
Date: Tue, 15 Oct 2024 23:16:39 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: mcgrof@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	samitolvanen@...gle.com, Matthew Maurer <mmaurer@...gle.com>, 
	Petr Pavlu <petr.pavlu@...e.com>, Daniel Gomez <da.gomez@...sung.com>
Subject: [PATCH 05/12] module: Factor out elf_validity_cache_index_info

Centralize .modinfo detection and property validation.

Signed-off-by: Matthew Maurer <mmaurer@...gle.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 473f1fb25de2..6747cbc774b0 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)
 {
@@ -1887,6 +1919,39 @@ 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.
@@ -1913,13 +1978,15 @@ 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;
 
@@ -1945,24 +2012,11 @@ 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)");
-- 
2.47.0.rc1.288.g06298d1525-goog