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Message-Id: <1534457824-7211-4-git-send-email-alex.popov@linux.com>
Date: Fri, 17 Aug 2018 01:17:00 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
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alex.popov@...ux.com
Subject: [PATCH v15 3/7] lkdtm: Add a test for STACKLEAK
Introduce an lkdtm test for the STACKLEAK feature: check that the
current task stack is properly erased (filled with STACKLEAK_POISON).
Signed-off-by: Alexander Popov <alex.popov@...ux.com>
Signed-off-by: Tycho Andersen <tycho@...ho.ws>
---
drivers/misc/lkdtm/Makefile | 2 ++
drivers/misc/lkdtm/core.c | 1 +
drivers/misc/lkdtm/lkdtm.h | 3 ++
drivers/misc/lkdtm/stackleak.c | 73 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 79 insertions(+)
create mode 100644 drivers/misc/lkdtm/stackleak.c
diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile
index 3370a41..951c984 100644
--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -8,7 +8,9 @@ lkdtm-$(CONFIG_LKDTM) += perms.o
lkdtm-$(CONFIG_LKDTM) += refcount.o
lkdtm-$(CONFIG_LKDTM) += rodata_objcopy.o
lkdtm-$(CONFIG_LKDTM) += usercopy.o
+lkdtm-$(CONFIG_LKDTM) += stackleak.o
+KASAN_SANITIZE_stackleak.o := n
KCOV_INSTRUMENT_rodata.o := n
OBJCOPYFLAGS :=
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index 2154d1b..aca26d8 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -183,6 +183,7 @@ static const struct crashtype crashtypes[] = {
CRASHTYPE(USERCOPY_STACK_FRAME_FROM),
CRASHTYPE(USERCOPY_STACK_BEYOND),
CRASHTYPE(USERCOPY_KERNEL),
+ CRASHTYPE(STACKLEAK_ERASING),
};
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index 9e513dc..b611b15 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -83,4 +83,7 @@ void lkdtm_USERCOPY_STACK_FRAME_FROM(void);
void lkdtm_USERCOPY_STACK_BEYOND(void);
void lkdtm_USERCOPY_KERNEL(void);
+/* lkdtm_stackleak.c */
+void lkdtm_STACKLEAK_ERASING(void);
+
#endif
diff --git a/drivers/misc/lkdtm/stackleak.c b/drivers/misc/lkdtm/stackleak.c
new file mode 100644
index 0000000..d5a0844
--- /dev/null
+++ b/drivers/misc/lkdtm/stackleak.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This code tests that the current task stack is properly erased (filled
+ * with STACKLEAK_POISON).
+ *
+ * Authors:
+ * Alexander Popov <alex.popov@...ux.com>
+ * Tycho Andersen <tycho@...ho.ws>
+ */
+
+#include "lkdtm.h"
+#include <linux/stackleak.h>
+
+void lkdtm_STACKLEAK_ERASING(void)
+{
+ unsigned long *sp, left, found, i;
+ const unsigned long check_depth =
+ STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
+
+ /*
+ * For the details about the alignment of the poison values, see
+ * the comment in stackleak_track_stack().
+ */
+ sp = PTR_ALIGN(&i, sizeof(unsigned long));
+
+ left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
+ sp--;
+
+ /*
+ * One 'long int' at the bottom of the thread stack is reserved
+ * and not poisoned.
+ */
+ if (left > 1) {
+ left--;
+ } else {
+ pr_err("FAIL: not enough stack space for the test\n");
+ return;
+ }
+
+ pr_info("checking unused part of the thread stack (%lu bytes)...\n",
+ left * sizeof(unsigned long));
+
+ /*
+ * Search for 'check_depth' poison values in a row (just like
+ * stackleak_erase() does).
+ */
+ for (i = 0, found = 0; i < left && found <= check_depth; i++) {
+ if (*(sp - i) == STACKLEAK_POISON)
+ found++;
+ else
+ found = 0;
+ }
+
+ if (found <= check_depth) {
+ pr_err("FAIL: thread stack is not erased (checked %lu bytes)\n",
+ i * sizeof(unsigned long));
+ return;
+ }
+
+ 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;
+ }
+ }
+
+ pr_info("OK: the rest of the thread stack is properly erased\n");
+ return;
+}
--
2.7.4
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