linux-kernel - [PATCH 5/6] lkdtm: crash on overwriting protected pmalloc var

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Date:   Tue, 27 Mar 2018 04:55:23 +0300
From:   Igor Stoppa <igor.stoppa@...wei.com>
To:     <willy@...radead.org>, <keescook@...omium.org>, <mhocko@...nel.org>
CC:     <david@...morbit.com>, <rppt@...ux.vnet.ibm.com>,
        <labbott@...hat.com>, <linux-security-module@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <kernel-hardening@...ts.openwall.com>, <igor.stoppa@...il.com>,
        Igor Stoppa <igor.stoppa@...wei.com>
Subject: [PATCH 5/6] lkdtm: crash on overwriting protected pmalloc var

Verify that pmalloc read-only protection is in place: trying to
overwrite a protected variable will crash the kernel.

Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>
---
 drivers/misc/lkdtm.h       |  1 +
 drivers/misc/lkdtm_core.c  |  3 +++
 drivers/misc/lkdtm_perms.c | 28 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index 9e513dcfd809..dcda3ae76ceb 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -38,6 +38,7 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void);
 void __init lkdtm_perms_init(void);
 void lkdtm_WRITE_RO(void);
 void lkdtm_WRITE_RO_AFTER_INIT(void);
+void lkdtm_WRITE_RO_PMALLOC(void);
 void lkdtm_WRITE_KERN(void);
 void lkdtm_EXEC_DATA(void);
 void lkdtm_EXEC_STACK(void);
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 2154d1bfd18b..c9fd42bda6ee 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -155,6 +155,9 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(ACCESS_USERSPACE),
 	CRASHTYPE(WRITE_RO),
 	CRASHTYPE(WRITE_RO_AFTER_INIT),
+#ifdef CONFIG_PROTECTABLE_MEMORY
+	CRASHTYPE(WRITE_RO_PMALLOC),
+#endif
 	CRASHTYPE(WRITE_KERN),
 	CRASHTYPE(REFCOUNT_INC_OVERFLOW),
 	CRASHTYPE(REFCOUNT_ADD_OVERFLOW),
diff --git a/drivers/misc/lkdtm_perms.c b/drivers/misc/lkdtm_perms.c
index 53b85c9d16b8..0ac9023fd2b0 100644
--- a/drivers/misc/lkdtm_perms.c
+++ b/drivers/misc/lkdtm_perms.c
@@ -9,6 +9,7 @@
 #include <linux/vmalloc.h>
 #include <linux/mman.h>
 #include <linux/uaccess.h>
+#include <linux/pmalloc.h>
 #include <asm/cacheflush.h>
 
 /* Whether or not to fill the target memory area with do_nothing(). */
@@ -104,6 +105,33 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
 	*ptr ^= 0xabcd1234;
 }
 
+#ifdef CONFIG_PROTECTABLE_MEMORY
+void lkdtm_WRITE_RO_PMALLOC(void)
+{
+	struct gen_pool *pool;
+	int *i;
+
+	pool = pmalloc_create_pool("pool", 0);
+	if (unlikely(!pool)) {
+		pr_info("Failed preparing pool for pmalloc test.");
+		return;
+	}
+
+	i = (int *)pmalloc(pool, sizeof(int), GFP_KERNEL);
+	if (unlikely(!i)) {
+		pr_info("Failed allocating memory for pmalloc test.");
+		pmalloc_destroy_pool(pool);
+		return;
+	}
+
+	*i = INT_MAX;
+	pmalloc_protect_pool(pool);
+
+	pr_info("attempting bad pmalloc write at %p\n", i);
+	*i = 0;
+}
+#endif
+
 void lkdtm_WRITE_KERN(void)
 {
 	size_t size;
-- 
2.14.1