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AJvYcCVe2LrKWM8/eympNibyTwP2A5sLSNjCyF20FIG1FAHQK4c6yDjiMtt9YMFQ46WLfIHWF55ED+o8CQ==@kvack.org X-Gm-Message-State: AOJu0YxbiLh7sP5IkH0ZzpwCyqqXZlXPZDocvw6b+TaqXo58e6QhpkjU qnLI7+Q4eCUauQ0DgaUTofFV0h6ojx57liUKT0rzJe3muEfTQB50etzomLMmHmSjzzfAV9w7wLM l15fe9N/DkLXQwfHvNUJk+ePaP+k= X-Google-Smtp-Source: AGHT+IF3xzr0IrXObxzfcb4O6iTkSAiTXc9nhGEbRAIOPwqQ1mUji7C3cQ8eLfyj/AtYZrMAEqNFPbXuGeOYTAsI9BM= X-Received: by 2002:a05:6402:3486:b0:5c8:bb09:b413 with SMTP id 4fb4d7f45d1cf-5c8bb09b89cmr1699747a12.0.1727887210576; Wed, 02 Oct 2024 09:40:10 -0700 (PDT) MIME-Version: 1.0 References: <20240927151438.2143936-1-snovitoll@gmail.com> In-Reply-To: From: Sabyrzhan Tasbolatov Date: Wed, 2 Oct 2024 21:39:57 +0500 Message-ID: Subject: Re: [PATCH] mm: instrument copy_from/to_kernel_nofault To: Marco Elver Cc: ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, akpm@linux-foundation.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: A9E944000B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ngootcxo36oygrtt6n7uq8386qy87t98 X-HE-Tag: 1727887212-842607 X-HE-Meta: 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 r7gVPhbR 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 2, 2024 at 9:00=E2=80=AFPM Marco Elver wrote= : > > On Fri, 27 Sept 2024 at 17:14, Sabyrzhan Tasbolatov = wrote: > > > > Instrument copy_from_kernel_nofault(), copy_to_kernel_nofault() > > with instrument_memcpy_before() for KASAN, KCSAN checks and > > instrument_memcpy_after() for KMSAN. > > There's a fundamental problem with instrumenting > copy_from_kernel_nofault() - it's meant to be a non-faulting helper, > i.e. if it attempts to read arbitrary kernel addresses, that's not a > problem because it won't fault and BUG. These may be used in places > that probe random memory, and KASAN may say that some memory is > invalid and generate a report - but in reality that's not a problem. > > In the Bugzilla bug, Andrey wrote: > > > KASAN should check both arguments of copy_from/to_kernel_nofault() for = accessibility when both are fault-safe. > > I don't see this patch doing it, or at least it's not explained. By > looking at the code, I see that it does the instrument_memcpy_before() > right after pagefault_disable(), which tells me that KASAN or other > tools will complain if a page is not faulted in. These helpers are > meant to be usable like that - despite their inherent unsafety, > there's little that I see that KASAN can help with. Hello, thanks for the comment! instrument_memcpy_before() has been replaced with instrument_read() and instrument_write() in commit 9e3f2b1ecdd4("mm, kasan: proper instrument _kernel_nofault"), and there are KASAN, KCSAN checks. > What _might_ be useful, is detecting copying faulted-in but > uninitialized memory to user space. So I think the only > instrumentation we want to retain is KMSAN instrumentation for the > copy_from_kernel_nofault() helper, and only if no fault was > encountered. > > Instrumenting copy_to_kernel_nofault() may be helpful to catch memory > corruptions, but only if faulted-in memory was accessed. If we need to have KMSAN only instrumentation for copy_from_user_nofault(), then AFAIU, in mm/kasan/kasan_test.c copy_from_to_kernel_nofault_oob() should have only copy_to_kernel_nofault() OOB kunit test to trigger KASAN. And copy_from_user_nofault() kunit test can be placed in mm/kmsan/kmsan_tes= t.c. I wonder if instrument_get_user macro is OK for src ptr in copy_from_kernel_nofault(). If this is true understanding, then there is no need to add kasan_disable_current(), kasan_enable_current() for kernel helpers functions that use copy_from_kernel_nofault(). > > > > Tested on x86_64 and arm64 with CONFIG_KASAN_SW_TAGS. > > On arm64 with CONFIG_KASAN_HW_TAGS, kunit test currently fails. > > Need more clarification on it - currently, disabled in kunit test. > > > > Reported-by: Andrey Konovalov > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=3D210505 > > Signed-off-by: Sabyrzhan Tasbolatov > > --- > > mm/kasan/kasan_test.c | 31 +++++++++++++++++++++++++++++++ > > mm/maccess.c | 8 ++++++-- > > 2 files changed, 37 insertions(+), 2 deletions(-) > > > > diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c > > index 567d33b49..329d81518 100644 > > --- a/mm/kasan/kasan_test.c > > +++ b/mm/kasan/kasan_test.c > > @@ -1944,6 +1944,36 @@ static void match_all_mem_tag(struct kunit *test= ) > > kfree(ptr); > > } > > > > +static void copy_from_to_kernel_nofault_oob(struct kunit *test) > > +{ > > + char *ptr; > > + char buf[128]; > > + size_t size =3D sizeof(buf); > > + > > + /* Not detecting fails currently with HW_TAGS */ > > + KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS); > > + > > + ptr =3D kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL); > > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > > + OPTIMIZER_HIDE_VAR(ptr); > > + > > + if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) { > > + /* Check that the returned pointer is tagged. */ > > + KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_M= IN); > > + KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_K= ERNEL); > > + } > > + > > + KUNIT_EXPECT_KASAN_FAIL(test, > > + copy_from_kernel_nofault(&buf[0], ptr, size)); > > + KUNIT_EXPECT_KASAN_FAIL(test, > > + copy_from_kernel_nofault(ptr, &buf[0], size)); > > + KUNIT_EXPECT_KASAN_FAIL(test, > > + copy_to_kernel_nofault(&buf[0], ptr, size)); > > + KUNIT_EXPECT_KASAN_FAIL(test, > > + copy_to_kernel_nofault(ptr, &buf[0], size)); > > + kfree(ptr); > > +} > > + > > static struct kunit_case kasan_kunit_test_cases[] =3D { > > KUNIT_CASE(kmalloc_oob_right), > > KUNIT_CASE(kmalloc_oob_left), > > @@ -2017,6 +2047,7 @@ static struct kunit_case kasan_kunit_test_cases[]= =3D { > > KUNIT_CASE(match_all_not_assigned), > > KUNIT_CASE(match_all_ptr_tag), > > KUNIT_CASE(match_all_mem_tag), > > + KUNIT_CASE(copy_from_to_kernel_nofault_oob), > > {} > > }; > > > > diff --git a/mm/maccess.c b/mm/maccess.c > > index 518a25667..2c4251df4 100644 > > --- a/mm/maccess.c > > +++ b/mm/maccess.c > > @@ -15,7 +15,7 @@ bool __weak copy_from_kernel_nofault_allowed(const vo= id *unsafe_src, > > > > #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) = \ > > while (len >=3D sizeof(type)) { = \ > > - __get_kernel_nofault(dst, src, type, err_label); = \ > > + __get_kernel_nofault(dst, src, type, err_label); = \ > > dst +=3D sizeof(type); = \ > > src +=3D sizeof(type); = \ > > len -=3D sizeof(type); = \ > > @@ -32,6 +32,7 @@ long copy_from_kernel_nofault(void *dst, const void *= src, size_t size) > > return -ERANGE; > > > > pagefault_disable(); > > + instrument_memcpy_before(dst, src, size); > > if (!(align & 7)) > > copy_from_kernel_nofault_loop(dst, src, size, u64, Efau= lt); > > if (!(align & 3)) > > @@ -39,6 +40,7 @@ long copy_from_kernel_nofault(void *dst, const void *= src, size_t size) > > if (!(align & 1)) > > copy_from_kernel_nofault_loop(dst, src, size, u16, Efau= lt); > > copy_from_kernel_nofault_loop(dst, src, size, u8, Efault); > > + instrument_memcpy_after(dst, src, size, 0); > > pagefault_enable(); > > return 0; > > Efault: > > @@ -49,7 +51,7 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault); > > > > #define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) = \ > > while (len >=3D sizeof(type)) { = \ > > - __put_kernel_nofault(dst, src, type, err_label); = \ > > + __put_kernel_nofault(dst, src, type, err_label); = \ > > dst +=3D sizeof(type); = \ > > src +=3D sizeof(type); = \ > > len -=3D sizeof(type); = \ > > @@ -63,6 +65,7 @@ long copy_to_kernel_nofault(void *dst, const void *sr= c, size_t size) > > align =3D (unsigned long)dst | (unsigned long)src; > > > > pagefault_disable(); > > + instrument_memcpy_before(dst, src, size); > > if (!(align & 7)) > > copy_to_kernel_nofault_loop(dst, src, size, u64, Efault= ); > > if (!(align & 3)) > > @@ -70,6 +73,7 @@ long copy_to_kernel_nofault(void *dst, const void *sr= c, size_t size) > > if (!(align & 1)) > > copy_to_kernel_nofault_loop(dst, src, size, u16, Efault= ); > > copy_to_kernel_nofault_loop(dst, src, size, u8, Efault); > > + instrument_memcpy_after(dst, src, size, 0); > > pagefault_enable(); > > return 0; > > Efault: > > -- > > 2.34.1 > > > > -- > > You received this message because you are subscribed to the Google Grou= ps "kasan-dev" group. > > To unsubscribe from this group and stop receiving emails from it, send = an email to kasan-dev+unsubscribe@googlegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/ms= gid/kasan-dev/20240927151438.2143936-1-snovitoll%40gmail.com.