linux-kernel - [PATCH v2 2/2] lkdtm: tests for FORTIFY

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <20200120045424.16147-3-dja@axtens.net>
Date:   Mon, 20 Jan 2020 15:54:24 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     kernel-hardening@...ts.openwall.com, akpm@...ux-foundation.org,
        keescook@...omium.org
Cc:     linux-kernel@...r.kernel.org, Daniel Axtens <dja@...ens.net>
Subject: [PATCH v2 2/2] lkdtm: tests for FORTIFY_SOURCE

Add code to test both:

 - runtime detection of the overrun of a structure. This covers the
   __builtin_object_size(x, 0) case. This test is called FORTIFY_OBJECT.

 - runtime detection of the overrun of a char array within a structure.
   This covers the __builtin_object_size(x, 1) case which can be used
   for some string functions. This test is called FORTIFY_SUBOBJECT.

Suggested-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Daniel Axtens <dja@...ens.net>
---
 drivers/misc/lkdtm/bugs.c  | 51 ++++++++++++++++++++++++++++++++++++++
 drivers/misc/lkdtm/core.c  |  2 ++
 drivers/misc/lkdtm/lkdtm.h |  2 ++
 3 files changed, 55 insertions(+)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index a4fdad04809a..77bf01ce7e0c 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -11,6 +11,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/task_stack.h>
 #include <linux/uaccess.h>
+#include <linux/slab.h>
 
 #ifdef CONFIG_X86_32
 #include <asm/desc.h>
@@ -376,3 +377,53 @@ void lkdtm_DOUBLE_FAULT(void)
 	panic("tried to double fault but didn't die\n");
 }
 #endif
+
+void lkdtm_FORTIFY_OBJECT(void)
+{
+	struct target {
+		char a[10];
+	} target[2] = {};
+	int result;
+
+	/*
+	 * Using volatile prevents the compiler from determining the value of
+	 * 'size' at compile time. Without that, we would get a compile error
+	 * rather than a runtime error.
+	 */
+	volatile int size = 11;
+
+	pr_info("trying to read past the end of a struct\n");
+
+	result = memcmp(&target[0], &target[1], size);
+
+	/* Print result to prevent the code from being eliminated */
+	pr_err("FAIL: fortify did not catch an object overread!\n"
+	       "\"%d\" was the memcmp result.\n", result);
+}
+
+void lkdtm_FORTIFY_SUBOBJECT(void)
+{
+	struct target {
+		char a[10];
+		char b[10];
+	} target;
+	char *src;
+
+	src = kmalloc(20, GFP_KERNEL);
+	strscpy(src, "over ten bytes", 20);
+
+	pr_info("trying to strcpy past the end of a member of a struct\n");
+
+	/*
+	 * strncpy(target.a, src, 20); will hit a compile error because the
+	 * compiler knows at build time that target.a < 20 bytes. Use strcpy()
+	 * to force a runtime error.
+	 */
+	strcpy(target.a, src);
+
+	/* Use target.a to prevent the code from being eliminated */
+	pr_err("FAIL: fortify did not catch an sub-object overrun!\n"
+	       "\"%s\" was copied.\n", target.a);
+
+	kfree(src);
+}
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index ee0d6e721441..78d22a23b4f9 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -117,6 +117,8 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
 	CRASHTYPE(UNSET_SMEP),
 	CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
+	CRASHTYPE(FORTIFY_OBJECT),
+	CRASHTYPE(FORTIFY_SUBOBJECT),
 	CRASHTYPE(OVERWRITE_ALLOCATION),
 	CRASHTYPE(WRITE_AFTER_FREE),
 	CRASHTYPE(READ_AFTER_FREE),
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index c56d23e37643..13f13421dc19 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -31,6 +31,8 @@ void lkdtm_UNSET_SMEP(void);
 #ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void);
 #endif
+void lkdtm_FORTIFY_OBJECT(void);
+void lkdtm_FORTIFY_SUBOBJECT(void);
 
 /* lkdtm_heap.c */
 void __init lkdtm_heap_init(void);
-- 
2.20.1