[PATCH drivers/misc v2 0/4] lkdtm: Various clean ups

[PATCH drivers/misc v2 0/4] lkdtm: Various clean ups

[Kees Cook]

Hi Greg,

(Since this was aleady pending, I just spun a v2, resent here.)

Can you please apply these patches to your drivers/misc tree for LKDTM?
It's mostly a collection of fixes and improvements and tweaks to the
selftest integration.

Thanks!

-Kees

v2: - add fix for UML build failures (Randy, Richard)
v1: https://lore.kernel.org/lkml/20200529200347.2464284-1-keescook@chromium.org/

Kees Cook (4):
  lkdtm: Avoid more compiler optimizations for bad writes
  lkdtm/heap: Avoid edge and middle of slabs
  selftests/lkdtm: Reset WARN_ONCE to avoid false negatives
  lkdtm: Make arch-specific tests always available

 drivers/misc/lkdtm/bugs.c               | 49 +++++++++++++------------
 drivers/misc/lkdtm/heap.c               |  9 +++--
 drivers/misc/lkdtm/lkdtm.h              |  2 -
 drivers/misc/lkdtm/perms.c              | 22 +++++++----
 drivers/misc/lkdtm/usercopy.c           |  7 +++-
 tools/testing/selftests/lkdtm/run.sh    |  6 +++
 tools/testing/selftests/lkdtm/tests.txt |  1 +
 7 files changed, 58 insertions(+), 38 deletions(-)

-- 
2.25.1

[PATCH drivers/misc v2 1/4] lkdtm: Avoid more compiler optimizations for bad writes

[Kees Cook]

It seems at least Clang is able to throw away writes it knows are
destined for read-only memory, which makes things like the WRITE_RO test
fail, as the write gets elided. Instead, force the variable to be
volatile, and make similar changes through-out other tests in an effort
to avoid needing to repeat fixing these kinds of problems. Also includes
pr_err() calls in failure paths so that kernel logs are more clear in
the failure case.

Reported-by: Prasad Sodagudi <psodagud@codeaurora.org>
Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Fixes: 9ae113ce5faf ("lkdtm: add tests for additional page permissions")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/misc/lkdtm/bugs.c     | 11 +++++------
 drivers/misc/lkdtm/perms.c    | 22 +++++++++++++++-------
 drivers/misc/lkdtm/usercopy.c |  7 +++++--
 3 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 736675f0a246..08c70281c380 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -118,9 +118,8 @@ noinline void lkdtm_CORRUPT_STACK(void)
 	/* Use default char array length that triggers stack protection. */
 	char data[8] __aligned(sizeof(void *));
 
-	__lkdtm_CORRUPT_STACK(&data);
-
-	pr_info("Corrupted stack containing char array ...\n");
+	pr_info("Corrupting stack containing char array ...\n");
+	__lkdtm_CORRUPT_STACK((void *)&data);
 }
 
 /* Same as above but will only get a canary with -fstack-protector-strong */
@@ -131,9 +130,8 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void)
 		unsigned long *ptr;
 	} data __aligned(sizeof(void *));
 
-	__lkdtm_CORRUPT_STACK(&data);
-
-	pr_info("Corrupted stack containing union ...\n");
+	pr_info("Corrupting stack containing union ...\n");
+	__lkdtm_CORRUPT_STACK((void *)&data);
 }
 
 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
@@ -248,6 +246,7 @@ void lkdtm_ARRAY_BOUNDS(void)
 
 	kfree(not_checked);
 	kfree(checked);
+	pr_err("FAIL: survived array bounds overflow!\n");
 }
 
 void lkdtm_CORRUPT_LIST_ADD(void)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 62f76d506f04..2dede2ef658f 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -57,6 +57,7 @@ static noinline void execute_location(void *dst, bool write)
 	}
 	pr_info("attempting bad execution at %px\n", func);
 	func();
+	pr_err("FAIL: func returned\n");
 }
 
 static void execute_user_location(void *dst)
@@ -75,20 +76,22 @@ static void execute_user_location(void *dst)
 		return;
 	pr_info("attempting bad execution at %px\n", func);
 	func();
+	pr_err("FAIL: func returned\n");
 }
 
 void lkdtm_WRITE_RO(void)
 {
-	/* Explicitly cast away "const" for the test. */
-	unsigned long *ptr = (unsigned long *)&rodata;
+	/* Explicitly cast away "const" for the test and make volatile. */
+	volatile unsigned long *ptr = (unsigned long *)&rodata;
 
 	pr_info("attempting bad rodata write at %px\n", ptr);
 	*ptr ^= 0xabcd1234;
+	pr_err("FAIL: survived bad write\n");
 }
 
 void lkdtm_WRITE_RO_AFTER_INIT(void)
 {
-	unsigned long *ptr = &ro_after_init;
+	volatile unsigned long *ptr = &ro_after_init;
 
 	/*
 	 * Verify we were written to during init. Since an Oops
@@ -102,19 +105,21 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
 
 	pr_info("attempting bad ro_after_init write at %px\n", ptr);
 	*ptr ^= 0xabcd1234;
+	pr_err("FAIL: survived bad write\n");
 }
 
 void lkdtm_WRITE_KERN(void)
 {
 	size_t size;
-	unsigned char *ptr;
+	volatile unsigned char *ptr;
 
 	size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
 	ptr = (unsigned char *)do_overwritten;
 
 	pr_info("attempting bad %zu byte write at %px\n", size, ptr);
-	memcpy(ptr, (unsigned char *)do_nothing, size);
+	memcpy((void *)ptr, (unsigned char *)do_nothing, size);
 	flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
+	pr_err("FAIL: survived bad write\n");
 
 	do_overwritten();
 }
@@ -193,9 +198,11 @@ void lkdtm_ACCESS_USERSPACE(void)
 	pr_info("attempting bad read at %px\n", ptr);
 	tmp = *ptr;
 	tmp += 0xc0dec0de;
+	pr_err("FAIL: survived bad read\n");
 
 	pr_info("attempting bad write at %px\n", ptr);
 	*ptr = tmp;
+	pr_err("FAIL: survived bad write\n");
 
 	vm_munmap(user_addr, PAGE_SIZE);
 }
@@ -203,19 +210,20 @@ void lkdtm_ACCESS_USERSPACE(void)
 void lkdtm_ACCESS_NULL(void)
 {
 	unsigned long tmp;
-	unsigned long *ptr = (unsigned long *)NULL;
+	volatile unsigned long *ptr = (unsigned long *)NULL;
 
 	pr_info("attempting bad read at %px\n", ptr);
 	tmp = *ptr;
 	tmp += 0xc0dec0de;
+	pr_err("FAIL: survived bad read\n");
 
 	pr_info("attempting bad write at %px\n", ptr);
 	*ptr = tmp;
+	pr_err("FAIL: survived bad write\n");
 }
 
 void __init lkdtm_perms_init(void)
 {
 	/* Make sure we can write to __ro_after_init values during __init */
 	ro_after_init |= 0xAA;
-
 }
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index e172719dd86d..b833367a45d0 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -304,19 +304,22 @@ void lkdtm_USERCOPY_KERNEL(void)
 		return;
 	}
 
-	pr_info("attempting good copy_to_user from kernel rodata\n");
+	pr_info("attempting good copy_to_user from kernel rodata: %px\n",
+		test_text);
 	if (copy_to_user((void __user *)user_addr, test_text,
 			 unconst + sizeof(test_text))) {
 		pr_warn("copy_to_user failed unexpectedly?!\n");
 		goto free_user;
 	}
 
-	pr_info("attempting bad copy_to_user from kernel text\n");
+	pr_info("attempting bad copy_to_user from kernel text: %px\n",
+		vm_mmap);
 	if (copy_to_user((void __user *)user_addr, vm_mmap,
 			 unconst + PAGE_SIZE)) {
 		pr_warn("copy_to_user failed, but lacked Oops\n");
 		goto free_user;
 	}
+	pr_err("FAIL: survived bad copy_to_user()\n");
 
 free_user:
 	vm_munmap(user_addr, PAGE_SIZE);
-- 
2.25.1

[PATCH drivers/misc v2 2/4] lkdtm/heap: Avoid edge and middle of slabs

[Kees Cook]

Har har, after I moved the slab freelist pointer into the middle of the
slab, now it looks like the contents are getting poisoned. Adjust the
test to avoid the freelist pointer again.

Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/misc/lkdtm/heap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
index 3c5cec85edce..1323bc16f113 100644
--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -58,11 +58,12 @@ void lkdtm_READ_AFTER_FREE(void)
 	int *base, *val, saw;
 	size_t len = 1024;
 	/*
-	 * The slub allocator uses the first word to store the free
-	 * pointer in some configurations. Use the middle of the
-	 * allocation to avoid running into the freelist
+	 * The slub allocator will use the either the first word or
+	 * the middle of the allocation to store the free pointer,
+	 * depending on configurations. Store in the second word to
+	 * avoid running into the freelist.
 	 */
-	size_t offset = (len / sizeof(*base)) / 2;
+	size_t offset = sizeof(*base);
 
 	base = kmalloc(len, GFP_KERNEL);
 	if (!base) {
-- 
2.25.1

[PATCH drivers/misc v2 3/4] selftests/lkdtm: Reset WARN_ONCE to avoid false negatives

[Kees Cook]

Since we expect to see warnings every time for many tests, just reset
the WARN_ONCE flags each time the script runs.

Fixes: 46d1a0f03d66 ("selftests/lkdtm: Add tests for LKDTM targets")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 tools/testing/selftests/lkdtm/run.sh | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
index ee64ff8df8f4..8383eb89d88a 100755
--- a/tools/testing/selftests/lkdtm/run.sh
+++ b/tools/testing/selftests/lkdtm/run.sh
@@ -8,6 +8,7 @@
 #
 set -e
 TRIGGER=/sys/kernel/debug/provoke-crash/DIRECT
+CLEAR_ONCE=/sys/kernel/debug/clear_warn_once
 KSELFTEST_SKIP_TEST=4
 
 # Verify we have LKDTM available in the kernel.
@@ -67,6 +68,11 @@ cleanup() {
 }
 trap cleanup EXIT
 
+# Reset WARN_ONCE counters so we trip it each time this runs.
+if [ -w $CLEAR_ONCE ] ; then
+	echo 1 > $CLEAR_ONCE
+fi
+
 # Save existing dmesg so we can detect new content below
 dmesg > "$DMESG"
 
-- 
2.25.1

[PATCH drivers/misc v2 4/4] lkdtm: Make arch-specific tests always available

[Kees Cook]

I'd like arch-specific tests to XFAIL when on a mismatched architecture
so that we can more easily compare test coverage across all systems.
Lacking kernel configs or CPU features count as a FAIL, not an XFAIL.

Additionally fixes a build failure under 32-bit UML.

Fixes: b09511c253e5 ("lkdtm: Add a DOUBLE_FAULT crash type on x86")
Fixes: cea23efb4de2 ("lkdtm/bugs: Make double-fault test always available")
Fixes: 6cb6982f42cb ("lkdtm: arm64: test kernel pointer authentication")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/misc/lkdtm/bugs.c               | 38 ++++++++++++++-----------
 drivers/misc/lkdtm/lkdtm.h              |  2 --
 tools/testing/selftests/lkdtm/tests.txt |  1 +
 3 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 08c70281c380..10338800f6be 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -13,7 +13,7 @@
 #include <linux/uaccess.h>
 #include <linux/slab.h>
 
-#ifdef CONFIG_X86_32
+#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
 #include <asm/desc.h>
 #endif
 
@@ -418,7 +418,7 @@ void lkdtm_UNSET_SMEP(void)
 
 void lkdtm_DOUBLE_FAULT(void)
 {
-#ifdef CONFIG_X86_32
+#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
 	/*
 	 * Trigger #DF by setting the stack limit to zero.  This clobbers
 	 * a GDT TLS slot, which is okay because the current task will die
@@ -453,38 +453,42 @@ void lkdtm_DOUBLE_FAULT(void)
 #endif
 }
 
-#ifdef CONFIG_ARM64_PTR_AUTH
+#ifdef CONFIG_ARM64
 static noinline void change_pac_parameters(void)
 {
-	/* Reset the keys of current task */
-	ptrauth_thread_init_kernel(current);
-	ptrauth_thread_switch_kernel(current);
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) {
+		/* Reset the keys of current task */
+		ptrauth_thread_init_kernel(current);
+		ptrauth_thread_switch_kernel(current);
+	}
 }
+#endif
 
-#define CORRUPT_PAC_ITERATE	10
 noinline void lkdtm_CORRUPT_PAC(void)
 {
+#ifdef CONFIG_ARM64
+#define CORRUPT_PAC_ITERATE	10
 	int i;
 
+	if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH))
+		pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH\n");
+
 	if (!system_supports_address_auth()) {
-		pr_err("FAIL: arm64 pointer authentication feature not present\n");
+		pr_err("FAIL: CPU lacks pointer authentication feature\n");
 		return;
 	}
 
-	pr_info("Change the PAC parameters to force function return failure\n");
+	pr_info("changing PAC parameters to force function return failure...\n");
 	/*
-	 * Pac is a hash value computed from input keys, return address and
+	 * PAC is a hash value computed from input keys, return address and
 	 * stack pointer. As pac has fewer bits so there is a chance of
 	 * collision, so iterate few times to reduce the collision probability.
 	 */
 	for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
 		change_pac_parameters();
 
-	pr_err("FAIL: %s test failed. Kernel may be unstable from here\n", __func__);
-}
-#else /* !CONFIG_ARM64_PTR_AUTH */
-noinline void lkdtm_CORRUPT_PAC(void)
-{
-	pr_err("FAIL: arm64 pointer authentication config disabled\n");
-}
+	pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n");
+#else
+	pr_err("XFAIL: this test is arm64-only\n");
 #endif
+}
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index 601a2156a0d4..8878538b2c13 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -31,9 +31,7 @@ void lkdtm_CORRUPT_USER_DS(void);
 void lkdtm_STACK_GUARD_PAGE_LEADING(void);
 void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
 void lkdtm_UNSET_SMEP(void);
-#ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void);
-#endif
 void lkdtm_CORRUPT_PAC(void);
 
 /* lkdtm_heap.c */
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index 92ca32143ae5..9d266e79c6a2 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -14,6 +14,7 @@ STACK_GUARD_PAGE_LEADING
 STACK_GUARD_PAGE_TRAILING
 UNSET_SMEP CR4 bits went missing
 DOUBLE_FAULT
+CORRUPT_PAC
 UNALIGNED_LOAD_STORE_WRITE
 #OVERWRITE_ALLOCATION Corrupts memory on failure
 #WRITE_AFTER_FREE Corrupts memory on failure
-- 
2.25.1