| 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
| ||
|
Message-Id: <20220413213917.711770-1-keescook@chromium.org>
Date: Wed, 13 Apr 2022 14:39:17 -0700
From: Kees Cook <keescook@...omium.org>
To: Dan Li <ashimida@...ux.alibaba.com>
Cc: Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] lkdtm: Add CFI_BACKWARD to test ROP mitigations
In order to test various backward-edge control flow integrity methods,
add a test that manipulates the return address on the stack. Currently
only arm64 Pointer Authentication and Shadow Call Stack is supported.
$ echo CFI_BACKWARD | cat >/sys/kernel/debug/provoke-crash/DIRECT
Under SCS, successful test of the mitigation is reported as:
lkdtm: Performing direct entry CFI_BACKWARD
lkdtm: Attempting unchecked stack return address redirection ...
lkdtm: ok: redirected stack return address.
lkdtm: Attempting checked stack return address redirection ...
lkdtm: ok: control flow unchanged.
Under PAC, successful test of the mitigation is reported by the PAC
exception handler.
If the CONFIGs are missing (or the mitigation isn't working), failure
is reported as:
lkdtm: Performing direct entry CFI_BACKWARD
lkdtm: Attempting unchecked stack return address redirection ...
lkdtm: ok: redirected stack return address.
lkdtm: Attempting checked stack return address redirection ...
lkdtm: FAIL: stack return address was redirected!
lkdtm: This is probably expected, since this kernel was built *without* CONFIG_ARM64_PTR_AUTH_KERNEL=y nor CONFIG_SHADOW_CALL_STACK=y
Co-developed-by: Dan Li <ashimida@...ux.alibaba.com>
Signed-off-by: Dan Li <ashimida@...ux.alibaba.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
drivers/misc/lkdtm/cfi.c | 130 ++++++++++++++++++++++++
tools/testing/selftests/lkdtm/tests.txt | 1 +
2 files changed, 131 insertions(+)
diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c
index e88f778be0d5..59ba983ff23e 100644
--- a/drivers/misc/lkdtm/cfi.c
+++ b/drivers/misc/lkdtm/cfi.c
@@ -42,8 +42,138 @@ static void lkdtm_CFI_FORWARD_PROTO(void)
pr_expected_config(CONFIG_CFI_CLANG);
}
+/*
+ * This can stay local to LKDTM, as there should not be a production reason
+ * to disable PAC && SCS.
+ */
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
+# ifdef CONFIG_ARM64_BTI_KERNEL
+# define __no_pac "branch-protection=bti"
+# else
+# define __no_pac "branch-protection=none"
+# endif
+# define __no_ret_protection __noscs __attribute__((__target__(__no_pac)))
+#else
+# define __no_ret_protection __noscs
+#endif
+
+/* The ultimate ROP gadget. */
+static noinline __no_ret_protection
+void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
+{
+ /* Use of volatile is to make sure final write isn't seen as a dead store. */
+ unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
+
+ /* Make sure we've found the right place on the stack before writing it. */
+ if(*ret_addr == expected)
+ *ret_addr = (addr);
+ else
+ /* Check architecture, stack layout, or compiler behavior... */
+ pr_warn("Eek: return address mismatch! %px != %px\n",
+ *ret_addr, addr);
+}
+
+static noinline
+void set_return_addr(unsigned long *expected, unsigned long *addr)
+{
+ /* Use of volatile is to make sure final write isn't seen as a dead store. */
+ unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
+
+ /* Make sure we've found the right place on the stack before writing it. */
+ if(*ret_addr == expected)
+ *ret_addr = (addr);
+ else
+ /* Check architecture, stack layout, or compiler behavior... */
+ pr_warn("Eek: return address mismatch! %px != %px\n",
+ *ret_addr, addr);
+}
+
+static volatile int force_check;
+
+static void lkdtm_CFI_BACKWARD(void)
+{
+ /* Use calculated gotos to keep labels addressable. */
+ void *labels[] = {0, &&normal, &&redirected, &&check_normal, &&check_redirected};
+
+ pr_info("Attempting unchecked stack return address redirection ...\n");
+
+ /* Always false */
+ if (force_check) {
+ /*
+ * Prepare to call with NULLs to avoid parameters being treated as
+ * constants in -02.
+ */
+ set_return_addr_unchecked(NULL, NULL);
+ set_return_addr(NULL, NULL);
+ if (force_check)
+ goto *labels[1];
+ if (force_check)
+ goto *labels[2];
+ if (force_check)
+ goto *labels[3];
+ if (force_check)
+ goto *labels[4];
+ return;
+ }
+
+ /*
+ * Use fallthrough switch case to keep basic block ordering between
+ * set_return_addr*() and the label after it.
+ */
+ switch (force_check) {
+ case 0:
+ set_return_addr_unchecked(&&normal, &&redirected);
+ fallthrough;
+ case 1:
+normal:
+ /* Always true */
+ if (!force_check) {
+ pr_err("FAIL: stack return address manipulation failed!\n");
+ /* If we can't redirect "normally", we can't test mitigations. */
+ return;
+ }
+ break;
+ default:
+redirected:
+ pr_info("ok: redirected stack return address.\n");
+ break;
+ }
+
+ pr_info("Attempting checked stack return address redirection ...\n");
+
+ switch (force_check) {
+ case 0:
+ set_return_addr(&&check_normal, &&check_redirected);
+ fallthrough;
+ case 1:
+check_normal:
+ /* Always true */
+ if (!force_check) {
+ pr_info("ok: control flow unchanged.\n");
+ return;
+ }
+
+check_redirected:
+ pr_err("FAIL: stack return address was redirected!\n");
+ break;
+ }
+
+ if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
+ pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL);
+ return;
+ }
+ if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
+ pr_expected_config(CONFIG_SHADOW_CALL_STACK);
+ return;
+ }
+ pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n",
+ lkdtm_kernel_info,
+ "CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK");
+}
+
static struct crashtype crashtypes[] = {
CRASHTYPE(CFI_FORWARD_PROTO),
+ CRASHTYPE(CFI_BACKWARD),
};
struct crashtype_category cfi_crashtypes = {
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index 243c781f0780..9dace01dbf15 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -74,6 +74,7 @@ USERCOPY_STACK_BEYOND
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
--
2.32.0
Powered by blists - more mailing lists