linux-kernel - [PATCH v3 2/2] extable: verify address is read-only

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Message-Id: <20170323025549.19588-3-ewk@edkovsky.org>
Date:   Wed, 22 Mar 2017 20:55:49 -0600
From:   Eddie Kovsky <ewk@...ovsky.org>
To:     jeyu@...hat.com, rusty@...tcorp.com.au, keescook@...omium.org
Cc:     linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: [PATCH v3 2/2] extable: verify address is read-only

Provide a mechanism to check if the address of a variable is
const or ro_after_init. It mimics the existing functions that test if an
address is inside the kernel's text section.

Other functions inside the kernel could then use this capability to
verify that their arguments are read-only.

Signed-off-by: Eddie Kovsky <ewk@...ovsky.org>
---
Changes in v3:
 - Fix missing declaration of is_module_rodata_address()

 include/linux/kernel.h |  2 ++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4c26dc3a8295..51beea39e6c4 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -444,6 +444,8 @@ extern int core_kernel_data(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
+extern int core_kernel_ro_data(unsigned long addr);
+extern int kernel_ro_address(unsigned long addr);

 unsigned long int_sqrt(unsigned long);

diff --git a/kernel/extable.c b/kernel/extable.c
index 2676d7f8baf6..3c3a9f4e6250 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -154,3 +154,32 @@ int func_ptr_is_kernel_text(void *ptr)
 		return 1;
 	return is_module_text_address(addr);
 }
+
+/**
+ * core_kernel_ro_data - Verify address points to read-only section
+ * @addr: address to test
+ *
+ */
+int core_kernel_ro_data(unsigned long addr)
+{
+	if (addr >= (unsigned long)__start_rodata &&
+	    addr < (unsigned long)__end_rodata)
+		return 1;
+
+	if (addr >= (unsigned long)__start_data_ro_after_init &&
+	    addr < (unsigned long)__end_data_ro_after_init)
+		return 1;
+
+	return 0;
+}
+
+/* Verify that address is const or ro_after_init. */
+int kernel_ro_address(unsigned long addr)
+{
+	if (core_kernel_ro_data(addr))
+		return 1;
+	if (is_module_rodata_address(addr))
+		return 1;
+
+	return 0;
+}
--
2.12.0