linux-kernel - [PATCH 2/3] module: Add a separate function to mark sections as read-only after init

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Message-ID: <20241223093840.29417-3-petr.pavlu@suse.com>
Date: Mon, 23 Dec 2024 10:37:48 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jason Baron <jbaron@...mai.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ard Biesheuvel <ardb@...nel.org>
Cc: linux-modules@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] module: Add a separate function to mark sections as read-only after init

Move the logic to mark special sections as read-only after module
initialization into a separate function, along other related code in
strict_rwx.c. Use a table with names of such sections to make it easier to
add more.

Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
---
 kernel/module/internal.h   |  2 ++
 kernel/module/main.c       | 18 +++---------------
 kernel/module/strict_rwx.c | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 7e78f6a8e85e..c4c918d9b65e 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -333,6 +333,8 @@ int module_enable_text_rox(const struct module *mod);
 int module_enforce_rwx_sections(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 				const char *secstrings,
 				const struct module *mod);
+void module_mark_ro_after_init(const Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
+			       const char *secstrings);
 
 #ifdef CONFIG_MODULE_SIG
 int module_sig_check(struct load_info *info, int flags);
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 5399c182b3cb..12ca6c6d7efd 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2710,7 +2710,6 @@ core_param(module_blacklist, module_blacklist, charp, 0400);
 static struct module *layout_and_allocate(struct load_info *info, int flags)
 {
 	struct module *mod;
-	unsigned int ndx;
 	int err;
 
 	/* Allow arches to frob section contents and sizes.  */
@@ -2728,22 +2727,11 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 	info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;
 
 	/*
-	 * Mark ro_after_init section with SHF_RO_AFTER_INIT so that
-	 * layout_sections() can put it in the right place.
+	 * Mark relevant sections as SHF_RO_AFTER_INIT so layout_sections() can
+	 * put them in the right place.
 	 * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
 	 */
-	ndx = find_sec(info, ".data..ro_after_init");
-	if (ndx)
-		info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
-	/*
-	 * Mark the __jump_table section as ro_after_init as well: these data
-	 * structures are never modified, with the exception of entries that
-	 * refer to code in the __init section, which are annotated as such
-	 * at module load time.
-	 */
-	ndx = find_sec(info, "__jump_table");
-	if (ndx)
-		info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+	module_mark_ro_after_init(info->hdr, info->sechdrs, info->secstrings);
 
 	/*
 	 * Determine total sizes, and put offsets in sh_entsize.  For now
diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
index d1c43309bb25..598f89195336 100644
--- a/kernel/module/strict_rwx.c
+++ b/kernel/module/strict_rwx.c
@@ -101,3 +101,36 @@ int module_enforce_rwx_sections(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 
 	return 0;
 }
+
+static const char *const ro_after_init[] = {
+	/*
+	 * Section .data..ro_after_init holds data explicitly annotated by
+	 * __ro_after_init.
+	 */
+	".data..ro_after_init",
+
+	/*
+	 * Section __jump_table holds data structures that are never modified,
+	 * with the exception of entries that refer to code in the __init
+	 * section, which are marked as such at module load time.
+	 */
+	"__jump_table",
+};
+
+void module_mark_ro_after_init(const Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
+			       const char *secstrings)
+{
+	int i, j;
+
+	for (i = 1; i < hdr->e_shnum; i++) {
+		Elf_Shdr *shdr = &sechdrs[i];
+
+		for (j = 0; j < ARRAY_SIZE(ro_after_init); j++) {
+			if (strcmp(secstrings + shdr->sh_name,
+				   ro_after_init[j]) == 0) {
+				shdr->sh_flags |= SHF_RO_AFTER_INIT;
+				break;
+			}
+		}
+	}
+}
-- 
2.43.0