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Tue, 12 Jan 2021 05:39:08 -0800 (PST) Date: Tue, 12 Jan 2021 14:39:03 +0100 From: Marco Elver To: Andrey Konovalov Subject: Re: [PATCH 08/11] kasan: adopt kmalloc_uaf2 test to HW_TAGS mode Message-ID: References: <9a4f47fe8717b4b249591b307cdd1f26c46dcb82.1609871239.git.andreyknvl@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <9a4f47fe8717b4b249591b307cdd1f26c46dcb82.1609871239.git.andreyknvl@google.com> User-Agent: Mutt/2.0.2 (2020-11-20) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210112_083912_008198_742A17EE X-CRM114-Status: GOOD ( 22.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, Branislav Rankov , Catalin Marinas , Kevin Brodsky , Will Deacon , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, Alexander Potapenko , Evgenii Stepanov , Andrey Ryabinin , Andrew Morton , Vincenzo Frascino , Dmitry Vyukov Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov wrote: > In the kmalloc_uaf2() test, the pointers to the two allocated memory > blocks might be the same, and the test will fail. With the software > tag-based mode, the probability of the that happening is 1/254, so it's > hard to observe the failure. For the hardware tag-based mode though, > the probablity is 1/14, which is quite noticable. > > Allow up to 4 attempts at generating different tags for the tag-based > modes. > > Signed-off-by: Andrey Konovalov > Link: https://linux-review.googlesource.com/id/Ibfa458ef2804ff465d8eb07434a300bf36388d55 > --- > lib/test_kasan.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > index b5077a47b95a..b67da7f6e17f 100644 > --- a/lib/test_kasan.c > +++ b/lib/test_kasan.c > @@ -375,7 +375,9 @@ static void kmalloc_uaf2(struct kunit *test) > { > char *ptr1, *ptr2; > size_t size = 43; > + int counter = 0; > > +again: > ptr1 = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1); > > @@ -384,6 +386,13 @@ static void kmalloc_uaf2(struct kunit *test) > ptr2 = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2); > > + /* > + * For tag-based KASAN ptr1 and ptr2 tags might happen to be the same. > + * Allow up to 4 attempts at generating different tags. > + */ > + if (!IS_ENABLED(CONFIG_KASAN_GENERIC) && ptr1 == ptr2 && counter++ < 4) > + goto again; > + Why do we even need a limit? Why not retry until ptr1 != ptr2? > KUNIT_EXPECT_KASAN_FAIL(test, ptr1[40] = 'x'); > KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2); > > -- > 2.29.2.729.g45daf8777d-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel