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Message-Id: <1507157703-14972-3-git-send-email-alex.popov@linux.com>
Date: Thu, 5 Oct 2017 01:55:02 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
keescook@...omium.org,
pageexec@...email.hu,
spender@...ecurity.net,
tycho@...ker.com,
Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Andy Lutomirski <luto@...capital.net>,
x86@...nel.org,
alex.popov@...ux.com
Subject: [PATCH RFC v4 2/3] lkdtm: Add a test for STACKLEAK
Introduce two lkdtm tests for the STACKLEAK feature: STACKLEAK_CHECK_ALLOCA
and STACKLEAK_TRACK_STACK. Both of them check that the current task stack
is properly erased (filled with STACKLEAK_POISON).
In addition, STACKLEAK_CHECK_ALLOCA tests that:
- check_alloca() allows alloca calls which don't exhaust the kernel stack;
- alloca calls which exhaust/overflow the kernel stack hit BUG() in
check_alloca().
And STACKLEAK_TRACK_STACK checks that exhausting the thread stack with a
recursion is detected:
- it hits the BUG() in track_stack() if CONFIG_VMAP_STACK is not enabled,
- or hits the guard page otherwise.
Signed-off-by: Tycho Andersen <tycho@...ker.com>
Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
drivers/misc/Makefile | 3 +
drivers/misc/lkdtm.h | 4 ++
drivers/misc/lkdtm_core.c | 2 +
drivers/misc/lkdtm_stackleak.c | 139 +++++++++++++++++++++++++++++++++++++++++
4 files changed, 148 insertions(+)
create mode 100644 drivers/misc/lkdtm_stackleak.c
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index d84819d..105e16e 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -63,6 +63,9 @@ lkdtm-$(CONFIG_LKDTM) += lkdtm_perms.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_refcount.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_usercopy.o
+lkdtm-$(CONFIG_LKDTM) += lkdtm_stackleak.o
+
+KASAN_SANITIZE_lkdtm_stackleak.o := n
KCOV_INSTRUMENT_lkdtm_rodata.o := n
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index bfb6c45..5952339 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -82,4 +82,8 @@ void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
void lkdtm_USERCOPY_STACK_BEYOND(void);
void lkdtm_USERCOPY_KERNEL(void);
+/* lkdtm_stackleak.c */
+void lkdtm_STACKLEAK_CHECK_ALLOCA(void);
+void lkdtm_STACKLEAK_TRACK_STACK(void);
+
#endif
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 981b3ef..264d948 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -251,6 +251,8 @@ struct crashtype crashtypes[] = {
CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
CRASHTYPE(USERCOPY_STACK_BEYOND),
CRASHTYPE(USERCOPY_KERNEL),
+ CRASHTYPE(STACKLEAK_CHECK_ALLOCA),
+ CRASHTYPE(STACKLEAK_TRACK_STACK),
};
diff --git a/drivers/misc/lkdtm_stackleak.c b/drivers/misc/lkdtm_stackleak.c
new file mode 100644
index 0000000..1f95ee3
--- /dev/null
+++ b/drivers/misc/lkdtm_stackleak.c
@@ -0,0 +1,139 @@
+/*
+ * This file tests a few aspects of the STACKLEAK feature:
+ * - the current task stack is properly erased (filled with STACKLEAK_POISON);
+ * - check_alloca() allows alloca calls which don't exhaust the kernel stack;
+ * - alloca calls which exhaust/overflow the kernel stack hit BUG() in
+ * check_alloca();
+ * - exhausting the thread stack with a recursion is detected: it hits the
+ * BUG() in track_stack() if CONFIG_VMAP_STACK is not enabled, or hits the
+ * guard page otherwise.
+ *
+ * Copyright (C) Docker, Inc. 2017
+ *
+ * Authors:
+ * Tycho Andersen <tycho@...ker.com>
+ * Alexander Popov <alex.popov@...ux.com>
+ */
+
+#include "lkdtm.h"
+#include <linux/sched.h>
+#include <linux/compiler.h>
+
+#ifndef CONFIG_GCC_PLUGIN_STACKLEAK
+# define STACKLEAK_POISON -0xBEEF
+# define CONFIG_STACKLEAK_TRACK_MIN_SIZE 100
+#endif
+
+static noinline bool stack_is_erased(void)
+{
+ unsigned long *sp, left, found, i;
+
+ /*
+ * For the details about the alignment of the poison values, see
+ * the comment in track_stack().
+ */
+ sp = PTR_ALIGN(&i, sizeof(unsigned long));
+
+ left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
+ sp--;
+
+ /*
+ * Two unsigned long ints at the bottom of the thread stack are
+ * reserved and not poisoned.
+ */
+ if (left <= 2)
+ return false;
+
+ left -= 2;
+ pr_info("checking unused part of the thread stack (%lu bytes)...\n",
+ left * sizeof(unsigned long));
+
+ /* Search for 17 poison values in a row (like erase_kstack() does) */
+ for (i = 0, found = 0; i < left && found < 17; i++) {
+ if (*(sp - i) == STACKLEAK_POISON)
+ found++;
+ else
+ found = 0;
+ }
+
+ if (found < 17) {
+ pr_err("FAIL: thread stack is not erased (checked %lu bytes)\n",
+ i * sizeof(unsigned long));
+ return false;
+ }
+
+ pr_info("first %lu bytes are unpoisoned\n",
+ (i - found) * sizeof(unsigned long));
+
+ /* The rest of thread stack should be erased */
+ for (; i < left; i++) {
+ if (*(sp - i) != STACKLEAK_POISON) {
+ pr_err("FAIL: thread stack is NOT properly erased\n");
+ return false;
+ }
+ }
+
+ pr_info("the rest of the thread stack is properly erased\n");
+ return true;
+}
+
+static noinline void do_alloca(unsigned long size)
+{
+ char buf[size];
+
+ /* So this doesn't get inlined or optimized out */
+ snprintf(buf, size, "hello world\n");
+}
+
+void lkdtm_STACKLEAK_CHECK_ALLOCA(void)
+{
+ unsigned long left = (unsigned long)&left & (THREAD_SIZE - 1);
+
+ if (!stack_is_erased())
+ return;
+
+ /* Try a small alloca to see if it works */
+ pr_info("try a small alloca of 16 bytes...\n");
+ do_alloca(16);
+ pr_info("small alloca is successful\n");
+
+ /* Try to hit the BUG() in check_alloca() */
+ pr_info("try a large alloca of %lu bytes (stack overflow)...\n", left);
+ do_alloca(left);
+ pr_err("FAIL: large alloca overstepped the thread stack boundary\n");
+}
+
+/*
+ * The stack frame size of recursion() is bigger than the
+ * CONFIG_STACKLEAK_TRACK_MIN_SIZE, hence that function is instrumented
+ * by the STACKLEAK gcc plugin and it calls track_stack() at the beginning.
+ */
+static noinline unsigned long recursion(unsigned long prev_sp)
+{
+ char buf[CONFIG_STACKLEAK_TRACK_MIN_SIZE + 42];
+ unsigned long sp = (unsigned long)&sp;
+
+ snprintf(buf, sizeof(buf), "hello world\n");
+
+ if (prev_sp < sp + THREAD_SIZE)
+ sp = recursion(prev_sp);
+
+ return sp;
+}
+
+void lkdtm_STACKLEAK_TRACK_STACK(void)
+{
+ unsigned long sp = (unsigned long)&sp;
+
+ if (!stack_is_erased())
+ return;
+
+ /*
+ * Exhaust the thread stack with a recursion. It should hit the
+ * BUG() in track_stack() if CONFIG_VMAP_STACK is not enabled, or
+ * access the guard page otherwise.
+ */
+ pr_info("try to exhaust the thread stack with the recursion...\n");
+ pr_err("FAIL: thread stack exhaustion (%lu bytes) is not detected\n",
+ sp - recursion(sp));
+}
--
2.7.4
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