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From:   Alexander Popov <alex.popov@linux.com>
To:     Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     notify@kernel.org
Subject: [PATCH v1 1/1] lkdtm/stackleak: Make the stack erasing test more verbose
Date:   Thu, 19 Dec 2019 17:54:16 +0300
Message-Id: <20191219145416.435508-1-alex.popov@linux.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@linux.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