linux-kernel - [PATCH v3] kunit: kasan_test: disable fortify string checker on kasan

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Message-Id: <20250801120236.2962642-1-yeoreum.yun@arm.com>
Date: Fri,  1 Aug 2025 13:02:36 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: thomas.weissschuh@...utronix.de,
	ryabinin.a.a@...il.com,
	glider@...gle.com,
	andreyknvl@...il.com,
	dvyukov@...gle.com,
	vincenzo.frascino@....com,
	akpm@...ux-foundation.org
Cc: kasan-dev@...glegroups.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH v3] kunit: kasan_test: disable fortify string checker on kasan_strings() test

Similar to commit 09c6304e38e4 ("kasan: test: fix compatibility with
FORTIFY_SOURCE") the kernel is panicing in kasan_string().

This is due to the `src` and `ptr` not being hidden from the optimizer
which would disable the runtime fortify string checker.

Call trace:
  __fortify_panic+0x10/0x20 (P)
  kasan_strings+0x980/0x9b0
  kunit_try_run_case+0x68/0x190
  kunit_generic_run_threadfn_adapter+0x34/0x68
  kthread+0x1c4/0x228
  ret_from_fork+0x10/0x20
 Code: d503233f a9bf7bfd 910003fd 9424b243 (d4210000)
 ---[ end trace 0000000000000000 ]---
 note: kunit_try_catch[128] exited with irqs disabled
 note: kunit_try_catch[128] exited with preempt_count 1
     # kasan_strings: try faulted: last
** replaying previous printk message **
     # kasan_strings: try faulted: last line seen mm/kasan/kasan_test_c.c:1600
     # kasan_strings: internal error occurred preventing test case from running: -4

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
Patch History
=============
from v2 to v3:
  - rewrite commit message.
  - Using OPTIMIZER_HIDE_VAR() instead of __NO_FORTIFY
  - https://lore.kernel.org/all/20250801092805.2602490-1-yeoreum.yun@arm.com/

from v1 to v2:
  - Using __NO_FORTIFY instead of skipping kasan_strings() when
    CONFIG_FORTIFY_SOURCE is enabled.
  - https://lore.kernel.org/all/aIs4rwZ1o53iTuP%2F@e129823.arm.com/
---
 mm/kasan/kasan_test_c.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index 5f922dd38ffa..a1a0e60645da 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1578,9 +1578,11 @@ static void kasan_strings(struct kunit *test)

 	ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);

 	src = kmalloc(KASAN_GRANULE_SIZE, GFP_KERNEL | __GFP_ZERO);
 	strscpy(src, "f0cacc1a0000000", KASAN_GRANULE_SIZE);
+	OPTIMIZER_HIDE_VAR(src);

 	/*
 	 * Make sure that strscpy() does not trigger KASAN if it overreads into
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}