linux-kernel - [PATCH 07/12] module: Factor out elf_validity_cache_index

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Message-ID: <20241015231651.3851138-8-mmaurer@google.com>
Date: Tue, 15 Oct 2024 23:16:41 +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 07/12] module: Factor out elf_validity_cache_index_sym

Centralize symbol table detection and property validation.

Signed-off-by: Matthew Maurer <mmaurer@...gle.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 b633347d5d98..955746649f37 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2013,6 +2013,39 @@ 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
@@ -2036,10 +2069,8 @@ 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)
@@ -2051,34 +2082,21 @@ 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. */
@@ -2099,9 +2117,6 @@ 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)
-- 
2.47.0.rc1.288.g06298d1525-goog