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Message-Id: <20211022223826.330653-3-keescook@chromium.org>
Date: Fri, 22 Oct 2021 15:38:26 -0700
From: Kees Cook <keescook@...omium.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Kees Cook <keescook@...omium.org>,
Ard Biesheuvel <ardb@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Shuah Khan <shuah@...nel.org>,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: [PATCH 2/2] lkdtm/bugs: Check that a per-task stack canary exists
Introduce REPORT_STACK_CANARY to check for differing stack canaries
between two processes (i.e. that an architecture is correctly implementing
per-task stack canaries), using the task_struct canary as the hint to
locate in the stack. Requires that one of the processes being tested
not be pid 1.
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
drivers/misc/lkdtm/bugs.c | 77 +++++++++++++++++++++++++
drivers/misc/lkdtm/core.c | 1 +
drivers/misc/lkdtm/lkdtm.h | 1 +
tools/testing/selftests/lkdtm/config | 1 +
tools/testing/selftests/lkdtm/tests.txt | 1 +
5 files changed, 81 insertions(+)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 41fa558675c4..f21854ac5cc2 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -153,6 +153,83 @@ void lkdtm_REPORT_STACK(void)
pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic));
}
+static pid_t stack_canary_pid;
+static unsigned long stack_canary;
+static unsigned long stack_canary_offset;
+
+static noinline void __lkdtm_REPORT_STACK_CANARY(void *stack)
+{
+ int i = 0;
+ pid_t pid = task_pid_nr(current);
+ unsigned long *canary = (unsigned long *)stack;
+ unsigned long current_offset = 0, init_offset = 0;
+
+ /* Do our best to find the canary in a 16 word window ... */
+ for (i = 1; i < 16; i++) {
+ canary = (unsigned long *)stack + i;
+#ifdef CONFIG_STACKPROTECTOR
+ if (*canary == current->stack_canary)
+ current_offset = i;
+ if (*canary == init_task.stack_canary)
+ init_offset = i;
+#endif
+ }
+
+ if (current_offset == 0) {
+ /*
+ * If the canary doesn't match what's in the task_struct,
+ * we're either using a global canary or the stack frame
+ * layout changed.
+ */
+ if (init_offset != 0) {
+ pr_err("FAIL: global stack canary found at offset %ld (canary for pid %d matches init_task's)!\n",
+ init_offset, pid);
+ } else {
+ pr_warn("FAIL: did not correctly locate stack canary :(\n");
+ pr_expected_config(CONFIG_STACKPROTECTOR);
+ }
+
+ return;
+ } else if (init_offset != 0) {
+ pr_warn("WARNING: found both current and init_task canaries nearby?!\n");
+ }
+
+ canary = (unsigned long *)stack + current_offset;
+ if (stack_canary_pid == 0) {
+ stack_canary = *canary;
+ stack_canary_pid = pid;
+ stack_canary_offset = current_offset;
+ pr_info("Recorded stack canary for pid %d at offset %ld\n",
+ stack_canary_pid, stack_canary_offset);
+ } else if (pid == stack_canary_pid) {
+ pr_warn("ERROR: saw pid %d again -- please use a new pid\n", pid);
+ } else {
+ if (current_offset != stack_canary_offset) {
+ pr_warn("ERROR: canary offset changed from %ld to %ld!?\n",
+ stack_canary_offset, current_offset);
+ return;
+ }
+
+ if (*canary == stack_canary) {
+ pr_warn("FAIL: canary identical for pid %d and pid %d at offset %ld!\n",
+ stack_canary_pid, pid, current_offset);
+ } else {
+ pr_info("ok: stack canaries differ between pid %d and pid %d at offset %ld.\n",
+ stack_canary_pid, pid, current_offset);
+ /* Reset the test. */
+ stack_canary_pid = 0;
+ }
+ }
+}
+
+void lkdtm_REPORT_STACK_CANARY(void)
+{
+ /* Use default char array length that triggers stack protection. */
+ char data[8] __aligned(sizeof(void *)) = { };
+
+ __lkdtm_REPORT_STACK_CANARY((void *)&data);
+}
+
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
{
static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index e99db37e56d5..d4c6cdced37b 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -111,6 +111,7 @@ static const struct crashtype crashtypes[] = {
CRASHTYPE(CORRUPT_STACK),
CRASHTYPE(CORRUPT_STACK_STRONG),
CRASHTYPE(REPORT_STACK),
+ CRASHTYPE(REPORT_STACK_CANARY),
CRASHTYPE(CORRUPT_LIST_ADD),
CRASHTYPE(CORRUPT_LIST_DEL),
CRASHTYPE(STACK_GUARD_PAGE_LEADING),
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index c212a253edde..d6137c70ebbe 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -69,6 +69,7 @@ void lkdtm_EXHAUST_STACK(void);
void lkdtm_CORRUPT_STACK(void);
void lkdtm_CORRUPT_STACK_STRONG(void);
void lkdtm_REPORT_STACK(void);
+void lkdtm_REPORT_STACK_CANARY(void);
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void);
void lkdtm_SOFTLOCKUP(void);
void lkdtm_HARDLOCKUP(void);
diff --git a/tools/testing/selftests/lkdtm/config b/tools/testing/selftests/lkdtm/config
index 38edea25631b..a26a3fa9e925 100644
--- a/tools/testing/selftests/lkdtm/config
+++ b/tools/testing/selftests/lkdtm/config
@@ -8,3 +8,4 @@ CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y
CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y
CONFIG_UBSAN_BOUNDS=y
CONFIG_UBSAN_TRAP=y
+CONFIG_STACKPROTECTOR_STRONG=y
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index 09f7bfa383cc..6b36b7f5dcf9 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -12,6 +12,7 @@ CORRUPT_LIST_ADD list_add corruption
CORRUPT_LIST_DEL list_del corruption
STACK_GUARD_PAGE_LEADING
STACK_GUARD_PAGE_TRAILING
+REPORT_STACK_CANARY repeat:2 ok: stack canaries differ
UNSET_SMEP pinned CR4 bits changed:
DOUBLE_FAULT
CORRUPT_PAC
--
2.30.2
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