linux-kernel - [PATCH v2 2/3] extable: verify address is read-only

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Message-Id: <20170218055844.1457-3-ewk@edkovsky.org>
Date:   Fri, 17 Feb 2017 22:58:43 -0700
From:   Eddie Kovsky <ewk@...ovsky.org>
To:     jeyu@...hat.com, rusty@...tcorp.com.au, keescook@...omium.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: [PATCH v2 2/3] 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.

Signed-off-by: Eddie Kovsky <ewk@...ovsky.org>
---
 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 6b0d09051efb..e9608f129730 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -149,3 +149,32 @@ 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_ro_address(addr))
+		return 1;
+
+	return 0;
+}
--
2.11.1