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Message-Id: <20220901065914.1417829-3-keescook@chromium.org>
Date: Wed, 31 Aug 2022 23:59:14 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH 2/2] lkdtm: Update tests for memcpy() run-time warnings
Clarify the LKDTM FORTIFY tests, and add tests for the mem*() family of
functions, now that run-time checking is distinct.
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Shuah Khan <shuah@...nel.org>
Cc: linux-kselftest@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
drivers/misc/lkdtm/fortify.c | 96 +++++++++++++++++++++----
tools/testing/selftests/lkdtm/tests.txt | 8 ++-
2 files changed, 88 insertions(+), 16 deletions(-)
diff --git a/drivers/misc/lkdtm/fortify.c b/drivers/misc/lkdtm/fortify.c
index 080293fa3c52..015927665678 100644
--- a/drivers/misc/lkdtm/fortify.c
+++ b/drivers/misc/lkdtm/fortify.c
@@ -10,28 +10,31 @@
static volatile int fortify_scratch_space;
-static void lkdtm_FORTIFIED_OBJECT(void)
+static void lkdtm_FORTIFY_STR_OBJECT(void)
{
struct target {
char a[10];
- } target[2] = {};
+ int foo;
+ } target[3] = {};
/*
* 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;
+ volatile int size = 20;
+
+ pr_info("trying to strcmp() past the end of a struct\n");
- pr_info("trying to read past the end of a struct\n");
+ strncpy(target[0].a, target[1].a, size);
/* Store result to global to prevent the code from being eliminated */
- fortify_scratch_space = memcmp(&target[0], &target[1], size);
+ fortify_scratch_space = target[0].a[3];
- pr_err("FAIL: fortify did not block an object overread!\n");
+ pr_err("FAIL: fortify did not block a strncpy() object write overflow!\n");
pr_expected_config(CONFIG_FORTIFY_SOURCE);
}
-static void lkdtm_FORTIFIED_SUBOBJECT(void)
+static void lkdtm_FORTIFY_STR_MEMBER(void)
{
struct target {
char a[10];
@@ -44,7 +47,7 @@ static void lkdtm_FORTIFIED_SUBOBJECT(void)
strscpy(src, "over ten bytes", size);
size = strlen(src) + 1;
- pr_info("trying to strncpy past the end of a member of a struct\n");
+ pr_info("trying to strncpy() past the end of a struct member...\n");
/*
* strncpy(target.a, src, 20); will hit a compile error because the
@@ -56,7 +59,72 @@ static void lkdtm_FORTIFIED_SUBOBJECT(void)
/* Store result to global to prevent the code from being eliminated */
fortify_scratch_space = target.a[3];
- pr_err("FAIL: fortify did not block an sub-object overrun!\n");
+ pr_err("FAIL: fortify did not block a strncpy() struct member write overflow!\n");
+ pr_expected_config(CONFIG_FORTIFY_SOURCE);
+
+ kfree(src);
+}
+
+static void lkdtm_FORTIFY_MEM_OBJECT(void)
+{
+ int before[10];
+ struct target {
+ char a[10];
+ int foo;
+ } target = {};
+ int after[10];
+ /*
+ * 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 = 20;
+
+ memset(before, 0, sizeof(before));
+ memset(after, 0, sizeof(after));
+ fortify_scratch_space = before[5];
+ fortify_scratch_space = after[5];
+
+ pr_info("trying to memcpy() past the end of a struct\n");
+
+ pr_info("0: %zu\n", __builtin_object_size(&target, 0));
+ pr_info("1: %zu\n", __builtin_object_size(&target, 1));
+ pr_info("s: %d\n", size);
+ memcpy(&target, &before, size);
+
+ /* Store result to global to prevent the code from being eliminated */
+ fortify_scratch_space = target.a[3];
+
+ pr_err("FAIL: fortify did not block a memcpy() object write overflow!\n");
+ pr_expected_config(CONFIG_FORTIFY_SOURCE);
+}
+
+static void lkdtm_FORTIFY_MEM_MEMBER(void)
+{
+ struct target {
+ char a[10];
+ char b[10];
+ } target;
+ volatile int size = 20;
+ char *src;
+
+ src = kmalloc(size, GFP_KERNEL);
+ strscpy(src, "over ten bytes", size);
+ size = strlen(src) + 1;
+
+ pr_info("trying to memcpy() past the end of a struct member...\n");
+
+ /*
+ * strncpy(target.a, src, 20); will hit a compile error because the
+ * compiler knows at build time that target.a < 20 bytes. Use a
+ * volatile to force a runtime error.
+ */
+ memcpy(target.a, src, size);
+
+ /* Store result to global to prevent the code from being eliminated */
+ fortify_scratch_space = target.a[3];
+
+ pr_err("FAIL: fortify did not block a memcpy() struct member write overflow!\n");
pr_expected_config(CONFIG_FORTIFY_SOURCE);
kfree(src);
@@ -67,7 +135,7 @@ static void lkdtm_FORTIFIED_SUBOBJECT(void)
* strscpy and generate a panic because there is a write overflow (i.e. src
* length is greater than dst length).
*/
-static void lkdtm_FORTIFIED_STRSCPY(void)
+static void lkdtm_FORTIFY_STRSCPY(void)
{
char *src;
char dst[5];
@@ -136,9 +204,11 @@ static void lkdtm_FORTIFIED_STRSCPY(void)
}
static struct crashtype crashtypes[] = {
- CRASHTYPE(FORTIFIED_OBJECT),
- CRASHTYPE(FORTIFIED_SUBOBJECT),
- CRASHTYPE(FORTIFIED_STRSCPY),
+ CRASHTYPE(FORTIFY_STR_OBJECT),
+ CRASHTYPE(FORTIFY_STR_MEMBER),
+ CRASHTYPE(FORTIFY_MEM_OBJECT),
+ CRASHTYPE(FORTIFY_MEM_MEMBER),
+ CRASHTYPE(FORTIFY_STRSCPY),
};
struct crashtype_category fortify_crashtypes = {
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index 65e53eb0840b..607b8d7e3ea3 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -75,7 +75,9 @@ USERCOPY_KERNEL
STACKLEAK_ERASING OK: the rest of the thread stack is properly erased
CFI_FORWARD_PROTO
CFI_BACKWARD call trace:|ok: control flow unchanged
-FORTIFIED_STRSCPY
-FORTIFIED_OBJECT
-FORTIFIED_SUBOBJECT
+FORTIFY_STRSCPY detected buffer overflow
+FORTIFY_STR_OBJECT detected buffer overflow
+FORTIFY_STR_MEMBER detected buffer overflow
+FORTIFY_MEM_OBJECT detected buffer overflow
+FORTIFY_MEM_MEMBER detected field-spanning write
PPC_SLB_MULTIHIT Recovered
--
2.34.1
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