From: "Paul E. McKenney" <paulmck@kernel.org>
To: Marco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrey Konovalov <andreyknvl@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Christoph Lameter <cl@linux.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Eric Dumazet <edumazet@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Hillf Danton <hdanton@sina.com>, Ingo Molnar <mingo@redhat.com>,
Jann Horn <jannh@google.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Jonathan Corbet <corbet@lwn.net>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Kees Cook <keescook@chromium.org>,
Mark Rutland <mark.rutland@arm.com>,
Pekka Enberg <penberg@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
SeongJae Park <sjpark@amazon.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH v3 10/10] kfence: add test suite
Date: Mon, 21 Sep 2020 10:48:27 -0700 [thread overview]
Message-ID: <20200921174827.GG29330@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <CANpmjNPiAvyn+oARU39yOx7zxMxV8JHiSS_41H+65D_-MKmk7A@mail.gmail.com>
On Mon, Sep 21, 2020 at 07:37:13PM +0200, Marco Elver wrote:
> On Mon, 21 Sep 2020 at 19:13, Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Mon, Sep 21, 2020 at 03:26:11PM +0200, Marco Elver wrote:
> > > Add KFENCE test suite, testing various error detection scenarios. Makes
> > > use of KUnit for test organization. Since KFENCE's interface to obtain
> > > error reports is via the console, the test verifies that KFENCE outputs
> > > expected reports to the console.
> > >
> > > Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> > > Co-developed-by: Alexander Potapenko <glider@google.com>
> > > Signed-off-by: Alexander Potapenko <glider@google.com>
> > > Signed-off-by: Marco Elver <elver@google.com>
> >
> > [ . . . ]
> >
> > > +/* Test SLAB_TYPESAFE_BY_RCU works. */
> > > +static void test_memcache_typesafe_by_rcu(struct kunit *test)
> > > +{
> > > + const size_t size = 32;
> > > + struct expect_report expect = {
> > > + .type = KFENCE_ERROR_UAF,
> > > + .fn = test_memcache_typesafe_by_rcu,
> > > + };
> > > +
> > > + setup_test_cache(test, size, SLAB_TYPESAFE_BY_RCU, NULL);
> > > + KUNIT_EXPECT_TRUE(test, test_cache); /* Want memcache. */
> > > +
> > > + expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
> > > + *expect.addr = 42;
> > > +
> > > + rcu_read_lock();
> > > + test_free(expect.addr);
> > > + KUNIT_EXPECT_EQ(test, *expect.addr, (char)42);
> > > + rcu_read_unlock();
> >
> > It won't happen very often, but memory really could be freed at this point,
> > especially in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels ...
>
> Ah, thanks for pointing it out.
>
> > > + /* No reports yet, memory should not have been freed on access. */
> > > + KUNIT_EXPECT_FALSE(test, report_available());
> >
> > ... so the above statement needs to go before the rcu_read_unlock().
>
> You mean the comment (and not the KUNIT_EXPECT_FALSE that no reports
> were generated), correct?
>
> Admittedly, the whole comment is a bit imprecise, so I'll reword.
I freely confess that I did not research exactly what might generate
a report. But if this KUNIT_EXPECT_FALSE() was just verifying that the
previous KUNIT_EXPECT_TRUE() did not trigger, then yes, the code is just
fine as it is.
Thanx, Paul
> > > + rcu_barrier(); /* Wait for free to happen. */
> >
> > But you are quite right that the memory is not -guaranteed- to be freed
> > until we get here.
>
> Right, I'll update the comment.
>
> Thanks,
> -- Marco
next prev parent reply other threads:[~2020-09-21 17:48 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 13:26 [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Marco Elver
2020-09-21 13:26 ` [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure Marco Elver
2020-09-25 11:23 ` SeongJae Park
2020-09-25 11:31 ` Marco Elver
2020-09-29 12:42 ` Andrey Konovalov
2020-09-29 13:11 ` Marco Elver
2020-09-29 13:48 ` Andrey Konovalov
2020-09-29 13:49 ` Marco Elver
2020-09-29 14:01 ` Andrey Konovalov
2020-09-29 14:24 ` Mark Rutland
2020-09-29 14:51 ` Marco Elver
2020-09-29 15:05 ` Mark Rutland
2020-10-05 16:00 ` Alexander Potapenko
2020-10-05 16:49 ` Jann Horn
2020-09-29 15:51 ` Alexander Potapenko
2020-10-01 18:11 ` Mark Rutland
2020-09-21 13:26 ` [PATCH v3 02/10] x86, kfence: enable KFENCE for x86 Marco Elver
2020-09-21 13:26 ` [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Marco Elver
2020-09-21 14:31 ` Will Deacon
2020-09-21 14:58 ` Alexander Potapenko
2020-09-21 15:37 ` Alexander Potapenko
2020-09-21 17:43 ` Will Deacon
2020-09-22 9:56 ` Marco Elver
2020-09-29 13:53 ` Mark Rutland
2020-09-29 16:52 ` Alexander Potapenko
2020-09-25 15:25 ` Alexander Potapenko
2020-09-29 14:02 ` Mark Rutland
2020-10-01 11:24 ` Alexander Potapenko
2020-10-01 17:57 ` Mark Rutland
2020-10-08 9:40 ` Marco Elver
2020-10-08 10:45 ` Mark Rutland
2020-10-14 19:12 ` Marco Elver
2020-10-15 13:39 ` Mark Rutland
2020-10-15 14:15 ` Marco Elver
2020-09-28 11:53 ` Marco Elver
2020-09-29 14:27 ` Mark Rutland
2020-09-29 17:04 ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 04/10] mm, kfence: insert KFENCE hooks for SLAB Marco Elver
2020-09-21 13:26 ` [PATCH v3 05/10] mm, kfence: insert KFENCE hooks for SLUB Marco Elver
2020-09-21 13:26 ` [PATCH v3 06/10] kfence, kasan: make KFENCE compatible with KASAN Marco Elver
2020-09-29 12:20 ` Andrey Konovalov
2020-09-29 13:13 ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 07/10] kfence, kmemleak: make KFENCE compatible with KMEMLEAK Marco Elver
2020-09-21 13:26 ` [PATCH v3 08/10] kfence, lockdep: make KFENCE compatible with lockdep Marco Elver
2020-09-21 13:26 ` [PATCH v3 09/10] kfence, Documentation: add KFENCE documentation Marco Elver
2020-09-21 13:26 ` [PATCH v3 10/10] kfence: add test suite Marco Elver
2020-09-21 17:13 ` Paul E. McKenney
2020-09-21 17:37 ` Marco Elver
2020-09-21 17:48 ` Paul E. McKenney [this message]
2020-09-21 13:38 ` [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Dmitry Vyukov
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