linux-kernel - [PATCH v2] lkdtm/bugs: Don't expect thread termination without CONFIG_UBSAN

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Date:   Mon, 11 Apr 2022 21:13:39 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2] lkdtm/bugs: Don't expect thread termination without CONFIG_UBSAN_TRAP

When you don't select CONFIG_UBSAN_TRAP, you get:

  # echo ARRAY_BOUNDS > /sys/kernel/debug/provoke-crash/DIRECT
[  102.265827] ================================================================================
[  102.278433] UBSAN: array-index-out-of-bounds in drivers/misc/lkdtm/bugs.c:342:16
[  102.287207] index 8 is out of range for type 'char [8]'
[  102.298722] ================================================================================
[  102.313712] lkdtm: FAIL: survived array bounds overflow!
[  102.318770] lkdtm: Unexpected! This kernel (5.16.0-rc1-s3k-dev-01884-g720dcf79314a ppc) was built with CONFIG_UBSAN_BOUNDS=y

It is not correct because when CONFIG_UBSAN_TRAP is not selected
you can't expect array bounds overflow to kill the thread.

Modify the logic so that when the kernel is built with
CONFIG_UBSAN_BOUNDS but without CONFIG_UBSAN_TRAP, you get a warning
about CONFIG_UBSAN_TRAP not been selected instead.

This also require a fix of pr_expected_config(), otherwise the
following error is encountered.

  CC      drivers/misc/lkdtm/bugs.o
drivers/misc/lkdtm/bugs.c: In function 'lkdtm_ARRAY_BOUNDS':
drivers/misc/lkdtm/bugs.c:351:2: error: 'else' without a previous 'if'
  351 |  else
      |  ^~~~

Fixes: c75be56e35b2 ("lkdtm/bugs: Add ARRAY_BOUNDS to selftests")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v2: Fix pr_expected_config(), otherwise it can't be used in an if/else sequence.
---
 drivers/misc/lkdtm/bugs.c  | 5 ++++-
 drivers/misc/lkdtm/lkdtm.h | 5 ++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index f21854ac5cc2..0f4dd9621b75 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -346,7 +346,10 @@ void lkdtm_ARRAY_BOUNDS(void)
 	kfree(not_checked);
 	kfree(checked);
 	pr_err("FAIL: survived array bounds overflow!\n");
-	pr_expected_config(CONFIG_UBSAN_BOUNDS);
+	if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))
+		pr_expected_config(CONFIG_UBSAN_TRAP);
+	else
+		pr_expected_config(CONFIG_UBSAN_BOUNDS);
 }
 
 void lkdtm_CORRUPT_LIST_ADD(void)
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index f508096e8fd9..9c21a4ca0482 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -8,15 +8,14 @@
 
 extern char *lkdtm_kernel_info;
 
-#define pr_expected_config(kconfig)				\
-{								\
+#define pr_expected_config(kconfig)	do {			\
 	if (IS_ENABLED(kconfig)) 				\
 		pr_err("Unexpected! This %s was built with " #kconfig "=y\n", \
 			lkdtm_kernel_info);			\
 	else							\
 		pr_warn("This is probably expected, since this %s was built *without* " #kconfig "=y\n", \
 			lkdtm_kernel_info);			\
-}
+} while (0)
 
 #ifndef MODULE
 int lkdtm_check_bool_cmdline(const char *param);
-- 
2.35.1