ANDROID: GKI: Add module load time symbol protection

Add CONFIG_MODULE_SIG_PROTECT to enable lookup for the unprotected symbols from the build time generated list of symbols. Module loading behavior will change as follows: - Allows Android GKI Modules signed using MODULE_SIG_ALL during build. - Allows other modules to load if they don't violate the access to Android GKI protected symbols. Loading will fail and return -EACCES (Permission denied) if these modules access the symbol which is not allowlisted via symbol list or exported by a GKI module. Bug: 232430739 Test: TH Signed-off-by: Ramji Jiyani <ramjiyani@google.com> Change-Id: I751b1951241b45712c20ac0e3878abd2152dd002
2022-09-21 14:26:52 -07:00 · 2022-09-21 14:26:52 -07:00 · e9669eeb2f
commit e9669eeb2f
parent bf7b376659
8 changed files with 200 additions and 8 deletions
--- a/arch/arm64/configs/gki_defconfig
+++ b/arch/arm64/configs/gki_defconfig
@ -81,6 +81,8 @@ CONFIG_SHADOW_CALL_STACK=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 CONFIG_MODVERSIONS=y
+CONFIG_MODULE_SIG=y
+CONFIG_MODULE_SIG_PROTECT=y
 CONFIG_BLK_DEV_ZONED=y
 CONFIG_BLK_INLINE_ENCRYPTION=y
 CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK=y
--- a/arch/x86/configs/gki_defconfig
+++ b/arch/x86/configs/gki_defconfig
@ -71,6 +71,8 @@ CONFIG_JUMP_LABEL=y
 CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 CONFIG_MODVERSIONS=y
+CONFIG_MODULE_SIG=y
+CONFIG_MODULE_SIG_PROTECT=y
 CONFIG_BLK_DEV_ZONED=y
 CONFIG_BLK_INLINE_ENCRYPTION=y
 CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK=y
--- a/kernel/module/Makefile
+++ b/kernel/module/Makefile
@ -10,6 +10,7 @@ KCOV_INSTRUMENT_module.o := n
 obj-y += main.o strict_rwx.o
 obj-$(CONFIG_MODULE_DECOMPRESS) += decompress.o
 obj-$(CONFIG_MODULE_SIG) += signing.o
+obj-$(CONFIG_MODULE_SIG_PROTECT) += gki_module.o
 obj-$(CONFIG_LIVEPATCH) += livepatch.o
 obj-$(CONFIG_MODULES_TREE_LOOKUP) += tree_lookup.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += debug_kmemleak.o
@ -19,3 +20,14 @@ obj-$(CONFIG_SYSFS) += sysfs.o
 obj-$(CONFIG_KGDB_KDB) += kdb.o
 obj-$(CONFIG_MODVERSIONS) += version.o
 obj-$(CONFIG_MODULE_UNLOAD_TAINT_TRACKING) += tracking.o
+
+#
+# ANDROID: GKI: Generate headerfile required for gki_module.o
+#
+# Dependencies on generated files need to be listed explicitly
+$(obj)/gki_module.o: $(obj)/gki_module_unprotected.h
+
+$(obj)/gki_module_unprotected.h: $(srctree)/scripts/gen_gki_modules_headers.sh \
+                                $(if $(wildcard ${OUT_DIR}/abi_symbollist.raw), ${OUT_DIR}/abi_symbollist.raw)
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/gen_gki_modules_headers.sh $@ \
+	"$(srctree)"
--- a/kernel/module/gki_module.c
+++ b/kernel/module/gki_module.c
@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2022 Google LLC
+ * Author: ramjiyani@google.com (Ramji Jiyani)
+ */
+
+#include <linux/bsearch.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/string.h>
+
+/*
+ * Build time generated header files
+ *
+ * gki_module_unprotected.h -- Symbols allowed to _access_ by unsigned modules
+ */
+#include "gki_module_unprotected.h"
+
+/* bsearch() comparision callback */
+static int cmp_name(const void *sym, const void *protected_sym)
+{
+	return strncmp(sym, protected_sym, MAX_UNPROTECTED_NAME_LEN);
+}
+
+/**
+ * gki_is_module_unprotected_symbol - Is a symbol unprotected for unsigned module?
+ *
+ * @name:	Symbol being checked in list of unprotected symbols
+ */
+bool gki_is_module_unprotected_symbol(const char *name)
+{
+	return bsearch(name, gki_unprotected_symbols, NO_OF_UNPROTECTED_SYMBOLS,
+		       MAX_UNPROTECTED_NAME_LEN, cmp_name) != NULL;
+}
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@ -303,3 +303,12 @@ static inline int same_magic(const char *amagic, const char *bmagic, bool has_cr
 	return strcmp(amagic, bmagic) == 0;
 }
 #endif /* CONFIG_MODVERSIONS */
+
+#ifdef CONFIG_MODULE_SIG_PROTECT
+extern bool gki_is_module_unprotected_symbol(const char *name);
+#else
+static inline bool gki_is_module_unprotected_symbol(const char *name)
+{
+	return true;
+}
+#endif /* CONFIG_MODULE_SIG_PROTECT */
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@ -1095,6 +1095,21 @@ static const struct kernel_symbol *resolve_symbol(struct module *mod,
 		goto getname;
 	}

+	/*
+	 * ANDROID: GKI:
+	 * In case of an unsigned module symbol resolves only if:
+	 * 1. Symbol is in the list of unprotected symbol list OR
+	 * 2. If symbol owner is not NULL i.e. owner is another module;
+	 *    it has to be an unsigned module and not signed GKI module
+	 *    to protect symbols exported by signed GKI modules.
+	 */
+	if (!mod->sig_ok &&
+	    !gki_is_module_unprotected_symbol(name) &&
+	    fsa.owner && fsa.owner->sig_ok) {
+		fsa.sym = ERR_PTR(-EACCES);
+		goto getname;
+	}
+
 	err = ref_module(mod, fsa.owner);
 	if (err) {
 		fsa.sym = ERR_PTR(err);
@ -1327,9 +1342,15 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
 			     ignore_undef_symbol(info->hdr->e_machine, name)))
 				break;

-			ret = PTR_ERR(ksym) ?: -ENOENT;
-			pr_warn("%s: Unknown symbol %s (err %d)\n",
-				mod->name, name, ret);
+			if (PTR_ERR(ksym) == -EACCES) {
+				ret = -EACCES;
+				pr_warn("%s: Protected symbol: %s (err %d)\n",
+					mod->name, name, ret);
+			} else {
+				ret = PTR_ERR(ksym) ?: -ENOENT;
+				pr_warn("%s: Unknown symbol %s (err %d)\n",
+					mod->name, name, ret);
+			}
 			break;

 		default:
@ -2749,6 +2770,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
 			       "kernel\n", mod->name);
 		add_taint_module(mod, TAINT_UNSIGNED_MODULE, LOCKDEP_STILL_OK);
 	}
+#else
+	mod->sig_ok = 0;
 #endif

 	/* To avoid stressing percpu allocator, do this once we're unique. */
--- a/kernel/module/signing.c
+++ b/kernel/module/signing.c
@ -19,8 +19,20 @@
 #undef MODULE_PARAM_PREFIX
 #define MODULE_PARAM_PREFIX "module."

+/*
+ * ANDROID: GKI:
+ * Only enforce signature if SIG_PROTECT is not set
+ */
+#ifndef CONFIG_MODULE_SIG_PROTECT
 static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
 module_param(sig_enforce, bool_enable_only, 0644);
+void set_module_sig_enforced(void)
+{
+	sig_enforce = true;
+}
+#else
+#define sig_enforce false
+#endif

 /*
 * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
@ -32,11 +44,6 @@ bool is_module_sig_enforced(void)
 }
 EXPORT_SYMBOL(is_module_sig_enforced);

-void set_module_sig_enforced(void)
-{
-	sig_enforce = true;
-}
-
 /*
 * Verify the signature on a module.
 */
@ -121,5 +128,13 @@ int module_sig_check(struct load_info *info, int flags)
 		return -EKEYREJECTED;
 	}

+/*
+ * ANDROID: GKI: Do not prevent loading of unsigned modules;
+ * as all modules except GKI modules are not signed.
+ */
+#ifndef CONFIG_MODULE_SIG_PROTECT
 	return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
+#else
+	return 0;
+#endif
 }
--- a/scripts/gen_gki_modules_headers.sh
+++ b/scripts/gen_gki_modules_headers.sh
@ -0,0 +1,94 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright 2022 Google LLC
+# Author: ramjiyani@google.com (Ramji Jiyani)
+#
+
+#
+# Generates header file with list of unprotected symbols
+#
+# Called By: KERNEL_SRC/kernel/Makefile if CONFIG_MODULE_SIG_PROTECT=y
+#
+# gki_module_unprotected.h: Symbols allowed to _access_ by unsigned modules
+#
+# If valid symbol file doesn't exists then still generates valid C header files for
+# compilation to proceed with no symbols to protect
+#
+
+# Collect arguments from Makefile
+TARGET=$1
+SRCTREE=$2
+
+set -e
+
+#
+# Common Definitions
+#
+# Use "make V=1" to debug this script.
+case "$KBUILD_VERBOSE" in
+*1*)
+	set -x
+	;;
+esac
+
+#
+# generate_header():
+# Args: $1 = Name of the header file
+#       $2 = Input symbol list
+#       $3 = Symbol type ("unprotected")
+#
+generate_header() {
+	local header_file=$1
+	local symbol_file=$2
+	local symbol_type=$3
+
+	if [ -f "${header_file}" ]; then
+		rm -f -- "${header_file}"
+	fi
+
+	# Find Maximum symbol name length if valid symbol_file exist
+	if [  -s "${symbol_file}" ]; then
+		# Skip 1st line (symbol header), Trim white spaces & +1 for null termination
+		local max_name_len=$(awk '
+				{
+					$1=$1;
+					if ( length > L && NR > 1) {
+						L=length
+					}
+				} END { print ++L }' "${symbol_file}")
+	else
+		# Set to 1 to generate valid C header file
+		local max_name_len=1
+	fi
+
+	# Header generation
+	cat > "${header_file}" <<- EOT
+	/*
+	 * DO NOT EDIT
+	 *
+	 * Build generated header file with unprotected symbols/exports
+	 */
+
+	#define NO_OF_$(printf ${symbol_type} | tr [:lower:] [:upper:])_SYMBOLS \\
+	$(printf '\t')(sizeof(gki_${symbol_type}_symbols) / sizeof(gki_${symbol_type}_symbols[0]))
+	#define MAX_$(printf ${symbol_type} | tr [:lower:] [:upper:])_NAME_LEN (${max_name_len})
+
+	static const char gki_${symbol_type}_symbols[][MAX_$(printf ${symbol_type} |
+							tr [:lower:] [:upper:])_NAME_LEN] = {
+	EOT
+
+	# If a valid symbol_file present add symbols in an array except the 1st line
+	if [  -s "${symbol_file}" ]; then
+		sed -e 's/^[ \t]*/\t"/;s/[ \t]*$/",/' "${symbol_file}" >> "${header_file}"
+	fi
+
+	# Terminate the file
+	echo "};" >> "${header_file}"
+}
+
+# Sorted list of vendor symbols
+GKI_VENDOR_SYMBOLS="${OUT_DIR}/abi_symbollist.raw"
+
+generate_header "${TARGET}" "${GKI_VENDOR_SYMBOLS}" "unprotected"
+