[PATCH v6 11/11] lkdtm: Add test for XPFO

Tycho Andersen
2017-09-07T17:37:17Z

From: Juerg Haefliger <juerg.haefliger@canonical.com>

This test simply reads from userspace memory via the kernel's linear
map.

v6: * drop an #ifdef, just let the test fail if XPFO is not supported
* add XPFO_SMP test to try and test the case when one CPU does an xpfo
unmap of an address, that it can't be used accidentally by other
CPUs.

Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Tycho Andersen <tycho@docker.com>
Tested-by: Marco Benatto <marco.antonio.780@gmail.com>
---
drivers/misc/Makefile | 1 +
drivers/misc/lkdtm.h | 5 ++
drivers/misc/lkdtm_core.c | 3 +
drivers/misc/lkdtm_xpfo.c | 194 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 203 insertions(+)

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index b0b766416306..8447b42a447d 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -62,6 +62,7 @@ lkdtm-$(CONFIG_LKDTM) += lkdtm_heap.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_perms.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_usercopy.o
+lkdtm-$(CONFIG_LKDTM) += lkdtm_xpfo.o

KCOV_INSTRUMENT_lkdtm_rodata.o := n

diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index 3b4976396ec4..34a6ee37f216 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -64,4 +64,9 @@ void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
void lkdtm_USERCOPY_STACK_BEYOND(void);
void lkdtm_USERCOPY_KERNEL(void);

+/* lkdtm_xpfo.c */
+void lkdtm_XPFO_READ_USER(void);
+void lkdtm_XPFO_READ_USER_HUGE(void);
+void lkdtm_XPFO_SMP(void);
+
#endif
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 42d2b8e31e6b..9544e329de4b 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -235,6 +235,9 @@ struct crashtype crashtypes[] = {
CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
CRASHTYPE(USERCOPY_STACK_BEYOND),
CRASHTYPE(USERCOPY_KERNEL),
+ CRASHTYPE(XPFO_READ_USER),
+ CRASHTYPE(XPFO_READ_USER_HUGE),
+ CRASHTYPE(XPFO_SMP),
};

diff --git a/drivers/misc/lkdtm_xpfo.c b/drivers/misc/lkdtm_xpfo.c
new file mode 100644
index 000000000000..d903063bdd0b
--- /dev/null
+++ b/drivers/misc/lkdtm_xpfo.c
@@ -0,0 +1,194 @@
+/*
+ * This is for all the tests related to XPFO (eXclusive Page Frame Ownership).
+ */
+
+#include "lkdtm.h"
+
+#include <linux/cpumask.h>
+#include <linux/mman.h>
+#include <linux/uaccess.h>
+#include <linux/xpfo.h>
+#include <linux/kthread.h>
+
+#include <linux/delay.h>
+#include <linux/sched/task.h>
+
+#define XPFO_DATA 0xdeadbeef
+
+static unsigned long do_map(unsigned long flags)
+{
+ unsigned long user_addr, user_data = XPFO_DATA;
+
+ user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+ PROT_READ | PROT_WRITE | PROT_EXEC,
+ flags, 0);
+ if (user_addr >= TASK_SIZE) {
+ pr_warn("Failed to allocate user memory\n");
+ return 0;
+ }
+
+ if (copy_to_user((void __user *)user_addr, &user_data,
+ sizeof(user_data))) {
+ pr_warn("copy_to_user failed\n");
+ goto free_user;
+ }
+
+ return user_addr;
+
+free_user:
+ vm_munmap(user_addr, PAGE_SIZE);
+ return 0;
+}
+
+static unsigned long *user_to_kernel(unsigned long user_addr)
+{
+ phys_addr_t phys_addr;
+ void *virt_addr;
+
+ phys_addr = user_virt_to_phys(user_addr);
+ if (!phys_addr) {
+ pr_warn("Failed to get physical address of user memory\n");
+ return NULL;
+ }
+
+ virt_addr = phys_to_virt(phys_addr);
+ if (phys_addr != virt_to_phys(virt_addr)) {
+ pr_warn("Physical address of user memory seems incorrect\n");
+ return NULL;
+ }
+
+ return virt_addr;
+}
+
+static void read_map(unsigned long *virt_addr)
+{
+ pr_info("Attempting bad read from kernel address %p\n", virt_addr);
+ if (*(unsigned long *)virt_addr == XPFO_DATA)
+ pr_err("FAIL: Bad read succeeded?!\n");
+ else
+ pr_err("FAIL: Bad read didn't fail but data is incorrect?!\n");
+}
+
+static void read_user_with_flags(unsigned long flags)
+{
+ unsigned long user_addr, *kernel;
+
+ user_addr = do_map(flags);
+ if (!user_addr) {
+ pr_err("FAIL: map failed\n");
+ return;
+ }
+
+ kernel = user_to_kernel(user_addr);
+ if (!kernel) {
+ pr_err("FAIL: user to kernel conversion failed\n");
+ goto free_user;
+ }
+
+ read_map(kernel);
+
+free_user:
+ vm_munmap(user_addr, PAGE_SIZE);
+}
+
+/* Read from userspace via the kernel's linear map. */
+void lkdtm_XPFO_READ_USER(void)
+{
+ read_user_with_flags(MAP_PRIVATE | MAP_ANONYMOUS);
+}
+
+void lkdtm_XPFO_READ_USER_HUGE(void)
+{
+ read_user_with_flags(MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB);
+}
+
+struct smp_arg {
+ unsigned long *virt_addr;
+ unsigned int cpu;
+};
+
+static int smp_reader(void *parg)
+{
+ struct smp_arg *arg = parg;
+ unsigned long *virt_addr;
+
+ if (arg->cpu != smp_processor_id()) {
+ pr_err("FAIL: scheduled on wrong CPU?\n");
+ return 0;
+ }
+
+ virt_addr = smp_cond_load_acquire(&arg->virt_addr, VAL != NULL);
+ read_map(virt_addr);
+
+ return 0;
+}
+
+#ifdef CONFIG_X86
+#define XPFO_SMP_KILLED SIGKILL
+#elif CONFIG_ARM64
+#define XPFO_SMP_KILLED SIGSEGV
+#else
+#error unsupported arch
+#endif
+
+/* The idea here is to read from the kernel's map on a different thread than
+ * did the mapping (and thus the TLB flushing), to make sure that the page
+ * faults on other cores too.
+ */
+void lkdtm_XPFO_SMP(void)
+{
+ unsigned long user_addr, *virt_addr;
+ struct task_struct *thread;
+ int ret;
+ struct smp_arg arg;
+
+ if (num_online_cpus() < 2) {
+ pr_err("not enough to do a multi cpu test\n");
+ return;
+ }
+
+ arg.virt_addr = NULL;
+ arg.cpu = (smp_processor_id() + 1) % num_online_cpus();
+ thread = kthread_create(smp_reader, &arg, "lkdtm_xpfo_test");
+ if (IS_ERR(thread)) {
+ pr_err("couldn't create kthread? %ld\n", PTR_ERR(thread));
+ return;
+ }
+
+ kthread_bind(thread, arg.cpu);
+ get_task_struct(thread);
+ wake_up_process(thread);
+
+ user_addr = do_map(MAP_PRIVATE | MAP_ANONYMOUS);
+ if (!user_addr)
+ goto kill_thread;
+
+ virt_addr = user_to_kernel(user_addr);
+ if (!virt_addr) {
+ /*
+ * let's store something that will fail, so we can unblock the
+ * thread
+ */
+ smp_store_release(&arg.virt_addr, &arg);
+ goto free_user;
+ }
+
+ smp_store_release(&arg.virt_addr, virt_addr);
+
+ /* there must be a better way to do this. */
+ while (1) {
+ if (thread->exit_state)
+ break;
+ msleep_interruptible(100);
+ }
+
+free_user:
+ if (user_addr)
+ vm_munmap(user_addr, PAGE_SIZE);
+
+kill_thread:
+ ret = kthread_stop(thread);
+ if (ret != XPFO_SMP_KILLED)
+ pr_err("FAIL: thread wasn't killed: %d\n", ret);
+ put_task_struct(thread);
+}
--
2.11.0