linux-kernel - [PATCH v1 1/1] lkdtm/stackleak: Make the stack erasing test more verbose

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Date:   Thu, 19 Dec 2019 17:54:16 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     notify@...nel.org
Subject: [PATCH v1 1/1] lkdtm/stackleak: Make the stack erasing test more verbose

Make the stack erasing test more verbose about the errors that it
can detect. BUG() in case of test failure is useful when the test
is running in a loop.

Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
 drivers/misc/lkdtm/stackleak.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/lkdtm/stackleak.c b/drivers/misc/lkdtm/stackleak.c
index d5a084475abc..d198de4d4c7e 100644
--- a/drivers/misc/lkdtm/stackleak.c
+++ b/drivers/misc/lkdtm/stackleak.c
@@ -16,6 +16,7 @@ void lkdtm_STACKLEAK_ERASING(void)
 	unsigned long *sp, left, found, i;
 	const unsigned long check_depth =
 			STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
+	bool test_failed = false;
 
 	/*
 	 * For the details about the alignment of the poison values, see
@@ -34,7 +35,8 @@ void lkdtm_STACKLEAK_ERASING(void)
 		left--;
 	} else {
 		pr_err("FAIL: not enough stack space for the test\n");
-		return;
+		test_failed = true;
+		goto end;
 	}
 
 	pr_info("checking unused part of the thread stack (%lu bytes)...\n",
@@ -52,22 +54,29 @@ void lkdtm_STACKLEAK_ERASING(void)
 	}
 
 	if (found <= check_depth) {
-		pr_err("FAIL: thread stack is not erased (checked %lu bytes)\n",
+		pr_err("FAIL: the erased part is not found (checked %lu bytes)\n",
 						i * sizeof(unsigned long));
-		return;
+		test_failed = true;
+		goto end;
 	}
 
-	pr_info("first %lu bytes are unpoisoned\n",
+	pr_info("the erased part begins after %lu not poisoned bytes\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_err("FAIL: bad value number %lu in the erased part: 0x%lx\n",
+								i, *(sp - i));
+			test_failed = true;
 		}
 	}
 
-	pr_info("OK: the rest of the thread stack is properly erased\n");
-	return;
+end:
+	if (test_failed) {
+		pr_err("FAIL: the thread stack is NOT properly erased\n");
+		BUG();
+	} else {
+		pr_info("OK: the rest of the thread stack is properly erased\n");
+	}
 }
-- 
2.23.0