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Message-ID: <aLVzNmN+G/usuJoE@e129823.arm.com>
Date: Mon, 1 Sep 2025 11:19:34 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: ryabinin.a.a@...il.com, glider@...gle.com, dvyukov@...gle.com,
vincenzo.frascino@....com, corbet@....net, catalin.marinas@....com,
will@...nel.org, akpm@...ux-foundation.org,
scott@...amperecomputing.com, jhubbard@...dia.com,
pankaj.gupta@....com, leitao@...ian.org, kaleshsingh@...gle.com,
maz@...nel.org, broonie@...nel.org, oliver.upton@...ux.dev,
james.morse@....com, ardb@...nel.org,
hardevsinh.palaniya@...iconsignals.io, david@...hat.com,
yang@...amperecomputing.com, kasan-dev@...glegroups.com,
workflows@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mm@...ck.org
Subject: Re: [PATCH v5 2/2] kasan: apply write-only mode in kasan kunit
testcases
Hi Andrey,
> On Wed, Aug 20, 2025 at 9:12 AM Yeoreum Yun <yeoreum.yun@....com> wrote:
> >
> > When KASAN is configured in write-only mode,
> > fetch/load operations do not trigger tag check faults.
> >
> > As a result, the outcome of some test cases may differ
> > compared to when KASAN is configured without write-only mode.
> >
> > Therefore, by modifying pre-exist testcases
> > check the write only makes tag check fault (TCF) where
> > writing is perform in "allocated memory" but tag is invalid
> > (i.e) redzone write in atomic_set() testcases.
> > Otherwise check the invalid fetch/read doesn't generate TCF.
> >
> > Also, skip some testcases affected by initial value
> > (i.e) atomic_cmpxchg() testcase maybe successd if
> > it passes valid atomic_t address and invalid oldaval address.
> > In this case, if invalid atomic_t doesn't have the same oldval,
> > it won't trigger write operation so the test will pass.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > ---
> > mm/kasan/kasan_test_c.c | 237 +++++++++++++++++++++++++++-------------
> > 1 file changed, 162 insertions(+), 75 deletions(-)
> >
> > diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> > index e0968acc03aa..cc0730aa18d1 100644
> > --- a/mm/kasan/kasan_test_c.c
> > +++ b/mm/kasan/kasan_test_c.c
> > @@ -94,11 +94,13 @@ static void kasan_test_exit(struct kunit *test)
> > }
> >
> > /**
> > - * KUNIT_EXPECT_KASAN_FAIL - check that the executed expression produces a
> > - * KASAN report; causes a KUnit test failure otherwise.
> > + * _KUNIT_EXPECT_KASAN_TEMPLATE - check that the executed expression produces
>
> Let's name this macro "KUNIT_EXPECT_KASAN_RESULT" and the last argument "fail".
>
> > + * a KASAN report or not; a KUnit test failure when it's different from @produce.
>
> ..; causes a KUnit test failure when the result is different from @fail.
Thanks for your suggestion.
I'll apply with these!
> > *
> > * @test: Currently executing KUnit test.
> > - * @expression: Expression that must produce a KASAN report.
> > + * @expr: Expression produce a KASAN report or not.
>
> Expression to be tested.
>
> > + * @expr_str: Expression string
>
Okay.
> Expression to be tested encoded as a string.
>
> > + * @produce: expression should produce a KASAN report.
>
> @fail: Whether expression should produce a KASAN report.
I'll change with this :)
>
> > *
> > * For hardware tag-based KASAN, when a synchronous tag fault happens, tag
> > * checking is auto-disabled. When this happens, this test handler reenables
> > @@ -110,25 +112,29 @@ static void kasan_test_exit(struct kunit *test)
> > * Use READ/WRITE_ONCE() for the accesses and compiler barriers around the
> > * expression to prevent that.
> > *
> > - * In between KUNIT_EXPECT_KASAN_FAIL checks, test_status.report_found is kept
> > + * In between _KUNIT_EXPECT_KASAN_TEMPLATE checks, test_status.report_found is kept
> > * as false. This allows detecting KASAN reports that happen outside of the
> > * checks by asserting !test_status.report_found at the start of
> > - * KUNIT_EXPECT_KASAN_FAIL and in kasan_test_exit.
> > + * _KUNIT_EXPECT_KASAN_TEMPLATE and in kasan_test_exit.
> > */
> > -#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
> > +#define _KUNIT_EXPECT_KASAN_TEMPLATE(test, expr, expr_str, produce) \
> > +do { \
> > if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) && \
> > kasan_sync_fault_possible()) \
> > migrate_disable(); \
> > KUNIT_EXPECT_FALSE(test, READ_ONCE(test_status.report_found)); \
> > barrier(); \
> > - expression; \
> > + expr; \
> > barrier(); \
> > if (kasan_async_fault_possible()) \
> > kasan_force_async_fault(); \
> > - if (!READ_ONCE(test_status.report_found)) { \
> > - KUNIT_FAIL(test, KUNIT_SUBTEST_INDENT "KASAN failure " \
> > - "expected in \"" #expression \
> > - "\", but none occurred"); \
> > + if (READ_ONCE(test_status.report_found) != produce) { \
> > + KUNIT_FAIL(test, KUNIT_SUBTEST_INDENT "KASAN %s " \
> > + "expected in \"" expr_str \
> > + "\", but %soccurred", \
> > + (produce ? "failure" : "success"), \
> > + (test_status.report_found ? \
> > + "" : "none ")); \
>
> Let's keep the message as is for the case when a KASAN report is expected; i.e.:
>
> KASAN failure expected in X, but none occurred
>
> And for the case when KASAN report is not expected, let's do:
>
> KASAN failure not expected in X, but occurred
Thanks. I'll change as your suggestion :)
>
> > } \
> > if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) && \
> > kasan_sync_fault_possible()) { \
> > @@ -141,6 +147,29 @@ static void kasan_test_exit(struct kunit *test)
> > WRITE_ONCE(test_status.async_fault, false); \
> > } while (0)
> >
> > +/*
> > + * KUNIT_EXPECT_KASAN_FAIL - check that the executed expression produces a
> > + * KASAN report; causes a KUnit test failure otherwise.
> > + *
> > + * @test: Currently executing KUnit test.
> > + * @expr: Expression produce a KASAN report.
>
> Expression that must produce a KASAN report.
Thanks.
>
> > + */
> > +#define KUNIT_EXPECT_KASAN_FAIL(test, expr) \
> > + _KUNIT_EXPECT_KASAN_TEMPLATE(test, expr, #expr, true)
> > +
> > +/*
> > + * KUNIT_EXPECT_KASAN_FAIL_READ - check that the executed expression produces
> > + * a KASAN report for read access.
> > + * It causes a KUnit test failure. if KASAN report isn't produced for read access.
> > + * For write access, it cause a KUnit test failure if a KASAN report is produced
>
> KUNIT_EXPECT_KASAN_FAIL_READ - check that the executed expression
> produces a KASAN report when the write-only mode is not enabled;
> causes a KUnit test failure otherwise.
>
> Note: At the moment, this macro does not check whether the produced
> KASAN report is a report about a bad read access. It is only intended
> for checking the write-only KASAN mode functionality without failing
> KASAN tests.
>
> > + *
> > + * @test: Currently executing KUnit test.
> > + * @expr: Expression doesn't produce a KASAN report.
>
> Expression that must only produce a KASAN report when the write-only
> mode is not enabled.
Thanks for your perfect suggsetion :)
>
> > + */
> > +#define KUNIT_EXPECT_KASAN_FAIL_READ(test, expr) \
> > + _KUNIT_EXPECT_KASAN_TEMPLATE(test, expr, #expr, \
> > + !kasan_write_only_enabled()) \
> > +
> > #define KASAN_TEST_NEEDS_CONFIG_ON(test, config) do { \
> > if (!IS_ENABLED(config)) \
> > kunit_skip((test), "Test requires " #config "=y"); \
> > @@ -183,8 +212,8 @@ static void kmalloc_oob_right(struct kunit *test)
> > KUNIT_EXPECT_KASAN_FAIL(test, ptr[size + 5] = 'y');
> >
> > /* Out-of-bounds access past the aligned kmalloc object. */
> > - KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] =
> > - ptr[size + KASAN_GRANULE_SIZE + 5]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ptr[0] =
> > + ptr[size + KASAN_GRANULE_SIZE + 5]);
> >
> > kfree(ptr);
> > }
> > @@ -198,7 +227,8 @@ static void kmalloc_oob_left(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > OPTIMIZER_HIDE_VAR(ptr);
> > - KUNIT_EXPECT_KASAN_FAIL(test, *ptr = *(ptr - 1));
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, *ptr = *(ptr - 1));
> > +
> > kfree(ptr);
> > }
> >
> > @@ -211,7 +241,8 @@ static void kmalloc_node_oob_right(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > OPTIMIZER_HIDE_VAR(ptr);
> > - KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = ptr[size]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ptr[0] = ptr[size]);
> > +
> > kfree(ptr);
> > }
> >
> > @@ -291,7 +322,7 @@ static void kmalloc_large_uaf(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> > kfree(ptr);
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)ptr)[0]);
> > }
> >
> > static void kmalloc_large_invalid_free(struct kunit *test)
> > @@ -323,7 +354,8 @@ static void page_alloc_oob_right(struct kunit *test)
> > ptr = page_address(pages);
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = ptr[size]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ptr[0] = ptr[size]);
> > +
> > free_pages((unsigned long)ptr, order);
> > }
> >
> > @@ -338,7 +370,7 @@ static void page_alloc_uaf(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> > free_pages((unsigned long)ptr, order);
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)ptr)[0]);
> > }
> >
> > static void krealloc_more_oob_helper(struct kunit *test,
> > @@ -455,10 +487,10 @@ static void krealloc_uaf(struct kunit *test)
> > ptr1 = kmalloc(size1, GFP_KERNEL);
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
> > kfree(ptr1);
> > -
>
> Keep this empty line.
Sorry for my bad habit :\
I'll restore all of uneccessary removal/adding line.
Thanks.
>
> > KUNIT_EXPECT_KASAN_FAIL(test, ptr2 = krealloc(ptr1, size2, GFP_KERNEL));
> > KUNIT_ASSERT_NULL(test, ptr2);
> > - KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)ptr1);
> > +
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, *(volatile char *)ptr1);
> > }
> >
> > static void kmalloc_oob_16(struct kunit *test)
> > @@ -501,7 +533,8 @@ static void kmalloc_uaf_16(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
> > kfree(ptr2);
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, *ptr1 = *ptr2);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, *ptr1 = *ptr2);
> > +
> > kfree(ptr1);
> > }
> >
> > @@ -640,8 +673,10 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
> > memset((char *)ptr, 0, 64);
> > OPTIMIZER_HIDE_VAR(ptr);
> > OPTIMIZER_HIDE_VAR(invalid_size);
> > - KUNIT_EXPECT_KASAN_FAIL(test,
> > - memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> > +
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test,
> > + memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> > +
> > kfree(ptr);
> > }
> >
> > @@ -654,7 +689,8 @@ static void kmalloc_uaf(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > kfree(ptr);
> > - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[8]);
> > +
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)ptr)[8]);
> > }
> >
> > static void kmalloc_uaf_memset(struct kunit *test)
> > @@ -701,7 +737,8 @@ static void kmalloc_uaf2(struct kunit *test)
> > goto again;
> > }
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr1)[40]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)ptr1)[40]);
> > +
> > KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2);
> >
> > kfree(ptr2);
> > @@ -727,19 +764,19 @@ static void kmalloc_uaf3(struct kunit *test)
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
> > kfree(ptr2);
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr1)[8]);
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, ((volatile char *)ptr1)[8]);
> > }
> >
> > static void kasan_atomics_helper(struct kunit *test, void *unsafe, void *safe)
> > {
> > int *i_unsafe = unsafe;
> >
> > - KUNIT_EXPECT_KASAN_FAIL(test, READ_ONCE(*i_unsafe));
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, READ_ONCE(*i_unsafe));
> > +
>
> No need for this empty line.
>
> > KUNIT_EXPECT_KASAN_FAIL(test, WRITE_ONCE(*i_unsafe, 42));
> > - KUNIT_EXPECT_KASAN_FAIL(test, smp_load_acquire(i_unsafe));
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, smp_load_acquire(i_unsafe));
> > KUNIT_EXPECT_KASAN_FAIL(test, smp_store_release(i_unsafe, 42));
> > -
>
> Keep this empty line.
>
> > - KUNIT_EXPECT_KASAN_FAIL(test, atomic_read(unsafe));
> > + KUNIT_EXPECT_KASAN_FAIL_READ(test, atomic_read(unsafe));
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_set(unsafe, 42));
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_add(42, unsafe));
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_sub(42, unsafe));
> > @@ -752,18 +789,35 @@ static void kasan_atomics_helper(struct kunit *test, void *unsafe, void *safe)
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_xchg(unsafe, 42));
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_cmpxchg(unsafe, 21, 42));
> > KUNIT_EXPECT_KASAN_FAIL(test, atomic_try_cmpxchg(unsafe, safe, 42));
> > - KUNIT_EXPECT_KASAN_FAIL(test, atomic_try_cmpxchg(safe, unsafe, 42));
> > +
> > + /*
> > + * The result of the test below may vary due to garbage values of unsafe in
> > + * store-only mode. Therefore, skip this test when KASAN is configured
> > + * in store-only mode.
>
> store-only => the write-only
>
> Here and below.
Thanks. I'll change them..
[...]
--
Sincerely,
Yeoreum Yun
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