* [PATCH] mm: instrument copy_from/to_kernel_nofault @ 2024-09-27 15:14 Sabyrzhan Tasbolatov 2024-10-02 15:59 ` Marco Elver 0 siblings, 1 reply; 5+ messages in thread From: Sabyrzhan Tasbolatov @ 2024-09-27 15:14 UTC (permalink / raw) To: ryabinin.a.a, glider, andreyknvl, dvyukov, vincenzo.frascino, akpm Cc: kasan-dev, linux-mm, linux-kernel, snovitoll Instrument copy_from_kernel_nofault(), copy_to_kernel_nofault() with instrument_memcpy_before() for KASAN, KCSAN checks and instrument_memcpy_after() for KMSAN. 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 <andreyknvl@gmail.com> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505 Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com> --- 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 = sizeof(buf); + + /* Not detecting fails currently with HW_TAGS */ + KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS); + + ptr = 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_MIN); + KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); + } + + 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[] = { KUNIT_CASE(kmalloc_oob_right), KUNIT_CASE(kmalloc_oob_left), @@ -2017,6 +2047,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { 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 void *unsafe_src, #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \ while (len >= sizeof(type)) { \ - __get_kernel_nofault(dst, src, type, err_label); \ + __get_kernel_nofault(dst, src, type, err_label); \ dst += sizeof(type); \ src += sizeof(type); \ len -= 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, Efault); 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, Efault); 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 >= sizeof(type)) { \ - __put_kernel_nofault(dst, src, type, err_label); \ + __put_kernel_nofault(dst, src, type, err_label); \ dst += sizeof(type); \ src += sizeof(type); \ len -= sizeof(type); \ @@ -63,6 +65,7 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) align = (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 *src, 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: instrument copy_from/to_kernel_nofault 2024-09-27 15:14 [PATCH] mm: instrument copy_from/to_kernel_nofault Sabyrzhan Tasbolatov @ 2024-10-02 15:59 ` Marco Elver 2024-10-02 16:39 ` Sabyrzhan Tasbolatov 0 siblings, 1 reply; 5+ messages in thread From: Marco Elver @ 2024-10-02 15:59 UTC (permalink / raw) To: Sabyrzhan Tasbolatov Cc: ryabinin.a.a, glider, andreyknvl, dvyukov, vincenzo.frascino, akpm, kasan-dev, linux-mm, linux-kernel On Fri, 27 Sept 2024 at 17:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> 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. 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. > 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 <andreyknvl@gmail.com> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505 > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com> > --- > 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 = sizeof(buf); > + > + /* Not detecting fails currently with HW_TAGS */ > + KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS); > + > + ptr = 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_MIN); > + KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); > + } > + > + 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[] = { > KUNIT_CASE(kmalloc_oob_right), > KUNIT_CASE(kmalloc_oob_left), > @@ -2017,6 +2047,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { > 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 void *unsafe_src, > > #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \ > while (len >= sizeof(type)) { \ > - __get_kernel_nofault(dst, src, type, err_label); \ > + __get_kernel_nofault(dst, src, type, err_label); \ > dst += sizeof(type); \ > src += sizeof(type); \ > len -= 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, Efault); > 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, Efault); > 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 >= sizeof(type)) { \ > - __put_kernel_nofault(dst, src, type, err_label); \ > + __put_kernel_nofault(dst, src, type, err_label); \ > dst += sizeof(type); \ > src += sizeof(type); \ > len -= sizeof(type); \ > @@ -63,6 +65,7 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) > align = (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 *src, 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 Groups "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/msgid/kasan-dev/20240927151438.2143936-1-snovitoll%40gmail.com. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: instrument copy_from/to_kernel_nofault 2024-10-02 15:59 ` Marco Elver @ 2024-10-02 16:39 ` Sabyrzhan Tasbolatov 2024-10-04 6:55 ` Marco Elver 0 siblings, 1 reply; 5+ messages in thread From: Sabyrzhan Tasbolatov @ 2024-10-02 16:39 UTC (permalink / raw) To: Marco Elver Cc: ryabinin.a.a, glider, andreyknvl, dvyukov, vincenzo.frascino, akpm, kasan-dev, linux-mm, linux-kernel On Wed, Oct 2, 2024 at 9:00 PM Marco Elver <elver@google.com> wrote: > > On Fri, 27 Sept 2024 at 17:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> 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_test.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 <andreyknvl@gmail.com> > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505 > > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com> > > --- > > 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 = sizeof(buf); > > + > > + /* Not detecting fails currently with HW_TAGS */ > > + KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS); > > + > > + ptr = 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_MIN); > > + KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); > > + } > > + > > + 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[] = { > > KUNIT_CASE(kmalloc_oob_right), > > KUNIT_CASE(kmalloc_oob_left), > > @@ -2017,6 +2047,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { > > 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 void *unsafe_src, > > > > #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \ > > while (len >= sizeof(type)) { \ > > - __get_kernel_nofault(dst, src, type, err_label); \ > > + __get_kernel_nofault(dst, src, type, err_label); \ > > dst += sizeof(type); \ > > src += sizeof(type); \ > > len -= 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, Efault); > > 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, Efault); > > 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 >= sizeof(type)) { \ > > - __put_kernel_nofault(dst, src, type, err_label); \ > > + __put_kernel_nofault(dst, src, type, err_label); \ > > dst += sizeof(type); \ > > src += sizeof(type); \ > > len -= sizeof(type); \ > > @@ -63,6 +65,7 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) > > align = (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 *src, 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 Groups "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/msgid/kasan-dev/20240927151438.2143936-1-snovitoll%40gmail.com. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: instrument copy_from/to_kernel_nofault 2024-10-02 16:39 ` Sabyrzhan Tasbolatov @ 2024-10-04 6:55 ` Marco Elver 2024-10-04 12:37 ` Sabyrzhan Tasbolatov 0 siblings, 1 reply; 5+ messages in thread From: Marco Elver @ 2024-10-04 6:55 UTC (permalink / raw) To: Sabyrzhan Tasbolatov Cc: ryabinin.a.a, glider, andreyknvl, dvyukov, vincenzo.frascino, akpm, kasan-dev, linux-mm, linux-kernel On Wed, 2 Oct 2024 at 18:40, Sabyrzhan Tasbolatov <snovitoll@gmail.com> wrote: > > On Wed, Oct 2, 2024 at 9:00 PM Marco Elver <elver@google.com> wrote: > > > > On Fri, 27 Sept 2024 at 17:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> 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 Did you mean s/copy_from_user_nofault/copy_from_kernel_nofault/? > 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_test.c. I think in the interest of reducing false positives, I'd proceed with making copy_from_kernel_nofault() KMSAN only. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: instrument copy_from/to_kernel_nofault 2024-10-04 6:55 ` Marco Elver @ 2024-10-04 12:37 ` Sabyrzhan Tasbolatov 0 siblings, 0 replies; 5+ messages in thread From: Sabyrzhan Tasbolatov @ 2024-10-04 12:37 UTC (permalink / raw) To: Marco Elver Cc: ryabinin.a.a, glider, andreyknvl, dvyukov, vincenzo.frascino, akpm, kasan-dev, linux-mm, linux-kernel On Fri, Oct 4, 2024 at 11:55 AM Marco Elver <elver@google.com> wrote: > > On Wed, 2 Oct 2024 at 18:40, Sabyrzhan Tasbolatov <snovitoll@gmail.com> wrote: > > > > On Wed, Oct 2, 2024 at 9:00 PM Marco Elver <elver@google.com> wrote: > > > > > > On Fri, 27 Sept 2024 at 17:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> 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 > > Did you mean s/copy_from_user_nofault/copy_from_kernel_nofault/? Yes, typo, sorry for the confusion. > > > 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_test.c. > > I think in the interest of reducing false positives, I'd proceed with > making copy_from_kernel_nofault() KMSAN only. Here is my current upcoming patch that I will send separately once it's tested, it's slowly being compiled on my laptop (away from PC). I've moved copy_from_kernel_nofault() to kmsan_test.c and added kmsan_check_memory() _before_ pagefault_disable() to check kernel src address if it's initialized. For copy_to_kernel_nofault() , I've left instrument_write() for memory corruption check but before pagefault_disable() again, if I understood the logic correctly. I will adjust kmsan kunit test once I can run it and send a PATCH. Meanwhile, please let me know if the order of instrumentation before pagefault_disable() is correct. > 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. --- mm/kasan/kasan_test_c.c | 8 ++------ mm/kmsan/kmsan_test.c | 16 ++++++++++++++++ mm/maccess.c | 5 +++-- 3 files changed, 21 insertions(+), 8 deletions(-) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index 0a226ab032d..5cff90f831d 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1954,7 +1954,7 @@ static void rust_uaf(struct kunit *test) KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf()); } -static void copy_from_to_kernel_nofault_oob(struct kunit *test) +static void copy_to_kernel_nofault_oob(struct kunit *test) { char *ptr; char buf[128]; @@ -1973,10 +1973,6 @@ static void copy_from_to_kernel_nofault_oob(struct kunit *test) KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL); } - 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, @@ -2057,7 +2053,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { 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), + KUNIT_CASE(copy_to_kernel_nofault_oob), KUNIT_CASE(rust_uaf), {} }; diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c index 13236d579eb..fc50d0aef47 100644 --- a/mm/kmsan/kmsan_test.c +++ b/mm/kmsan/kmsan_test.c @@ -640,6 +640,21 @@ static void test_unpoison_memory(struct kunit *test) KUNIT_EXPECT_TRUE(test, report_matches(&expect)); } +static void test_copy_from_kernel_nofault(struct kunit *test) +{ + long ret; + volatile char src[4], dst[4]; + + EXPECTATION_UNINIT_VALUE_FN(expect, "test_copy_from_kernel_nofault"); + kunit_info( + test, + "testing copy_from_kernel_nofault with src uninitialized memory\n"); + + ret = copy_from_kernel_nofault(dst, src, sizeof(src)); + USE(ret); + KUNIT_EXPECT_TRUE(test, report_matches(&expect)); +} + static struct kunit_case kmsan_test_cases[] = { KUNIT_CASE(test_uninit_kmalloc), KUNIT_CASE(test_init_kmalloc), @@ -664,6 +679,7 @@ static struct kunit_case kmsan_test_cases[] = { KUNIT_CASE(test_long_origin_chain), KUNIT_CASE(test_stackdepot_roundtrip), KUNIT_CASE(test_unpoison_memory), + KUNIT_CASE(test_copy_from_kernel_nofault), {}, }; diff --git a/mm/maccess.c b/mm/maccess.c index f752f0c0fa3..a91a39a56cf 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -31,8 +31,9 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size) if (!copy_from_kernel_nofault_allowed(src, size)) return -ERANGE; + /* Make sure uninitialized kernel memory isn't copied. */ + kmsan_check_memory(src, size); pagefault_disable(); - instrument_read(src, size); if (!(align & 7)) copy_from_kernel_nofault_loop(dst, src, size, u64, Efault); if (!(align & 3)) @@ -63,8 +64,8 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) align = (unsigned long)dst | (unsigned long)src; - pagefault_disable(); instrument_write(dst, size); + pagefault_disable(); if (!(align & 7)) copy_to_kernel_nofault_loop(dst, src, size, u64, Efault); if (!(align & 3)) -- 2.34.1 ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-10-04 12:37 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-09-27 15:14 [PATCH] mm: instrument copy_from/to_kernel_nofault Sabyrzhan Tasbolatov 2024-10-02 15:59 ` Marco Elver 2024-10-02 16:39 ` Sabyrzhan Tasbolatov 2024-10-04 6:55 ` Marco Elver 2024-10-04 12:37 ` Sabyrzhan Tasbolatov
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