linux-kernel - [PATCH v2 10/10] module loader: enforce symbol import protection

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Message-ID: <20251013153918.2206045-11-sidnayyar@google.com>
Date: Mon, 13 Oct 2025 15:39:18 +0000
From: Siddharth Nayyar <sidnayyar@...gle.com>
To: petr.pavlu@...e.com
Cc: arnd@...db.de, linux-arch@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	mcgrof@...nel.org, nathan@...nel.org, nicolas.schier@...ux.dev, 
	samitolvanen@...gle.com, sidnayyar@...gle.com, maennich@...gle.com, 
	gprocida@...gle.com
Subject: [PATCH v2 10/10] module loader: enforce symbol import protection

The module loader will reject unsigned modules from loading if such a
module attempts to import a symbol which has the import protection bit
set in the kflagstab entry for the symbol.

Signed-off-by: Siddharth Nayyar <sidnayyar@...gle.com>
Reviewed-by: Petr Pavlu <petr.pavlu@...e.com>
---
 kernel/module/internal.h |  1 +
 kernel/module/main.c     | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 061161cc79d9..98faaf8900aa 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -108,6 +108,7 @@ struct find_symbol_arg {
 	const u32 *crc;
 	const struct kernel_symbol *sym;
 	enum mod_license license;
+	bool is_protected;
 };
 
 /* modules using other modules */
diff --git a/kernel/module/main.c b/kernel/module/main.c
index f5f9872dc070..c27df62a68f5 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -380,6 +380,7 @@ static bool find_exported_symbol_in_section(const struct symsearch *syms,
 	fsa->crc = symversion(syms->crcs, sym - syms->start);
 	fsa->sym = sym;
 	fsa->license = (sym_flags & KSYM_FLAG_GPL_ONLY) ? GPL_ONLY : NOT_GPL_ONLY;
+	fsa->is_protected = sym_flags & KSYM_FLAG_PROTECTED;
 
 	return true;
 }
@@ -1267,6 +1268,13 @@ static const struct kernel_symbol *resolve_symbol(struct module *mod,
 		goto getname;
 	}
 
+	if (fsa.is_protected && !mod->sig_ok) {
+		pr_warn("%s: Cannot use protected symbol %s\n",
+			mod->name, name);
+		fsa.sym = ERR_PTR(-EACCES);
+		goto getname;
+	}
+
 	err = ref_module(mod, fsa.owner);
 	if (err) {
 		fsa.sym = ERR_PTR(err);
@@ -1550,7 +1558,7 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
 				break;
 
 			ret = PTR_ERR(ksym) ?: -ENOENT;
-			pr_warn("%s: Unknown symbol %s (err %d)\n",
+			pr_warn("%s: Unresolved symbol %s (err %d)\n",
 				mod->name, name, ret);
 			break;
 
-- 
2.51.0.740.g6adb054d12-goog