* [PATCH 0/2] lkdtm/bugs: Check that a per-task stack canary exists
@ 2021-10-22 22:38 Kees Cook
2021-10-22 22:38 ` [PATCH 1/2] selftests/lkdtm: Add way to repeat a test Kees Cook
2021-10-22 22:38 ` [PATCH 2/2] lkdtm/bugs: Check that a per-task stack canary exists Kees Cook
0 siblings, 2 replies; 3+ messages in thread
From: Kees Cook @ 2021-10-22 22:38 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Kees Cook, Ard Biesheuvel, Arnd Bergmann, Shuah Khan,
linux-kernel, linux-kselftest, linux-hardening
Hi,
This adds a test for per-task stack canaries to help verify the latest
work in this area for arm[1]. Most architectures already support this
under GCC, though there are some that are still lagging[2].
-Kees
[1] https://lore.kernel.org/r/20211021142516.1843042-1-ardb@kernel.org
[2] https://github.com/KSPP/linux/issues/29
Kees Cook (2):
selftests/lkdtm: Add way to repeat a test
lkdtm/bugs: Check that a per-task stack canary exists
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/run.sh | 10 +++-
tools/testing/selftests/lkdtm/tests.txt | 1 +
6 files changed, 90 insertions(+), 1 deletion(-)
--
2.30.2
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH 1/2] selftests/lkdtm: Add way to repeat a test
2021-10-22 22:38 [PATCH 0/2] lkdtm/bugs: Check that a per-task stack canary exists Kees Cook
@ 2021-10-22 22:38 ` Kees Cook
2021-10-22 22:38 ` [PATCH 2/2] lkdtm/bugs: Check that a per-task stack canary exists Kees Cook
1 sibling, 0 replies; 3+ messages in thread
From: Kees Cook @ 2021-10-22 22:38 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Kees Cook, Ard Biesheuvel, Arnd Bergmann, Shuah Khan,
linux-kernel, linux-kselftest, linux-hardening
Some LKDTM tests need to be run more than once (usually to setup and
then later trigger). Until now, the only case was the SOFT_LOCKUP test,
which wasn't useful to run in the bulk selftests. The coming stack canary
checking needs to run twice, so support this with a new test output prefix
"repeat".
Signed-off-by: Kees Cook <keescook@chromium.org>
---
tools/testing/selftests/lkdtm/run.sh | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
index e95e79bd3126..95e904959207 100755
--- a/tools/testing/selftests/lkdtm/run.sh
+++ b/tools/testing/selftests/lkdtm/run.sh
@@ -56,8 +56,14 @@ if echo "$test" | grep -q '^#' ; then
fi
# If no expected output given, assume an Oops with back trace is success.
+repeat=1
if [ -z "$expect" ]; then
expect="call trace:"
+else
+ if echo "$expect" | grep -q '^repeat:' ; then
+ repeat=$(echo "$expect" | cut -d' ' -f1 | cut -d: -f2)
+ expect=$(echo "$expect" | cut -d' ' -f2-)
+ fi
fi
# Prepare log for report checking
@@ -83,7 +89,9 @@ dmesg > "$DMESG"
# the signal that killed the subprocess, we must ignore the failure and
# continue. However we don't silence stderr since there might be other
# useful details reported there in the case of other unexpected conditions.
-echo "$test" | cat >"$TRIGGER" || true
+for i in $(seq 1 $repeat); do
+ echo "$test" | cat >"$TRIGGER" || true
+done
# Record and dump the results
dmesg | comm --nocheck-order -13 "$DMESG" - > "$LOG" || true
--
2.30.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH 2/2] lkdtm/bugs: Check that a per-task stack canary exists
2021-10-22 22:38 [PATCH 0/2] lkdtm/bugs: Check that a per-task stack canary exists Kees Cook
2021-10-22 22:38 ` [PATCH 1/2] selftests/lkdtm: Add way to repeat a test Kees Cook
@ 2021-10-22 22:38 ` Kees Cook
1 sibling, 0 replies; 3+ messages in thread
From: Kees Cook @ 2021-10-22 22:38 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Kees Cook, Ard Biesheuvel, Arnd Bergmann, Shuah Khan,
linux-kernel, linux-kselftest, linux-hardening
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@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kees Cook <keescook@chromium.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
^ permalink raw reply related [flat|nested] 3+ messages in thread
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