| Message ID | 20211006035522.539346-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | kasan: test: Bypass __alloc_size checks | expand |
Hi Kees, On Tue, Oct 05, 2021 at 08:55:22PM -0700, Kees Cook wrote: > Intentional overflows, as performed by the KASAN tests, are detected > at compile time[1] (instead of only at run-time) with the addition of > __alloc_size. Fix this by forcing the compiler into not being able to > trust the size used following the kmalloc()s. It might be better to use OPTIMIZER_HIDE_VAR(), since that's intended to make the value opaque to the compiler, and volatile might not always do that depending on how the compiler tracks the variable. Thanks, Mark. > > [1] https://lore.kernel.org/lkml/20211005184717.65c6d8eb39350395e387b71f@linux-foundation.org > > Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> > Cc: Alexander Potapenko <glider@google.com> > Cc: Andrey Konovalov <andreyknvl@gmail.com> > Cc: Dmitry Vyukov <dvyukov@google.com> > Cc: kasan-dev@googlegroups.com > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > lib/test_kasan.c | 10 +++++----- > lib/test_kasan_module.c | 2 +- > 2 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > index 8835e0784578..0e1f8d5281b4 100644 > --- a/lib/test_kasan.c > +++ b/lib/test_kasan.c > @@ -435,7 +435,7 @@ static void kmalloc_uaf_16(struct kunit *test) > static void kmalloc_oob_memset_2(struct kunit *test) > { > char *ptr; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > > ptr = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > @@ -447,7 +447,7 @@ static void kmalloc_oob_memset_2(struct kunit *test) > static void kmalloc_oob_memset_4(struct kunit *test) > { > char *ptr; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > > ptr = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > @@ -459,7 +459,7 @@ static void kmalloc_oob_memset_4(struct kunit *test) > static void kmalloc_oob_memset_8(struct kunit *test) > { > char *ptr; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > > ptr = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > @@ -471,7 +471,7 @@ static void kmalloc_oob_memset_8(struct kunit *test) > static void kmalloc_oob_memset_16(struct kunit *test) > { > char *ptr; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > > ptr = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > @@ -483,7 +483,7 @@ static void kmalloc_oob_memset_16(struct kunit *test) > static void kmalloc_oob_in_memset(struct kunit *test) > { > char *ptr; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > > ptr = kmalloc(size, GFP_KERNEL); > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); > diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c > index 7ebf433edef3..c8cc77b1dcf3 100644 > --- a/lib/test_kasan_module.c > +++ b/lib/test_kasan_module.c > @@ -19,7 +19,7 @@ static noinline void __init copy_user_test(void) > { > char *kmem; > char __user *usermem; > - size_t size = 128 - KASAN_GRANULE_SIZE; > + volatile size_t size = 128 - KASAN_GRANULE_SIZE; > int __maybe_unused unused; > > kmem = kmalloc(size, GFP_KERNEL); > -- > 2.30.2 >
On Wed, Oct 06, 2021 at 12:38:36PM +0100, Mark Rutland wrote: > Hi Kees, > > On Tue, Oct 05, 2021 at 08:55:22PM -0700, Kees Cook wrote: > > Intentional overflows, as performed by the KASAN tests, are detected > > at compile time[1] (instead of only at run-time) with the addition of > > __alloc_size. Fix this by forcing the compiler into not being able to > > trust the size used following the kmalloc()s. > > It might be better to use OPTIMIZER_HIDE_VAR(), since that's intended to > make the value opaque to the compiler, and volatile might not always do > that depending on how the compiler tracks the variable. Given both you and Jann[1] have suggested this, I'll send a v2 with that. :) Thanks! -Kees [1] https://lore.kernel.org/lkml/CAG48ez19raco+s+UF8eiXqTvaDEoMAo6_qmW2KdO24QDpmZpFQ@mail.gmail.com/
diff --git a/lib/test_kasan.c b/lib/test_kasan.c index 8835e0784578..0e1f8d5281b4 100644 --- a/lib/test_kasan.c +++ b/lib/test_kasan.c @@ -435,7 +435,7 @@ static void kmalloc_uaf_16(struct kunit *test) static void kmalloc_oob_memset_2(struct kunit *test) { char *ptr; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); @@ -447,7 +447,7 @@ static void kmalloc_oob_memset_2(struct kunit *test) static void kmalloc_oob_memset_4(struct kunit *test) { char *ptr; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); @@ -459,7 +459,7 @@ static void kmalloc_oob_memset_4(struct kunit *test) static void kmalloc_oob_memset_8(struct kunit *test) { char *ptr; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); @@ -471,7 +471,7 @@ static void kmalloc_oob_memset_8(struct kunit *test) static void kmalloc_oob_memset_16(struct kunit *test) { char *ptr; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); @@ -483,7 +483,7 @@ static void kmalloc_oob_memset_16(struct kunit *test) static void kmalloc_oob_in_memset(struct kunit *test) { char *ptr; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c index 7ebf433edef3..c8cc77b1dcf3 100644 --- a/lib/test_kasan_module.c +++ b/lib/test_kasan_module.c @@ -19,7 +19,7 @@ static noinline void __init copy_user_test(void) { char *kmem; char __user *usermem; - size_t size = 128 - KASAN_GRANULE_SIZE; + volatile size_t size = 128 - KASAN_GRANULE_SIZE; int __maybe_unused unused; kmem = kmalloc(size, GFP_KERNEL);
Intentional overflows, as performed by the KASAN tests, are detected at compile time[1] (instead of only at run-time) with the addition of __alloc_size. Fix this by forcing the compiler into not being able to trust the size used following the kmalloc()s. [1] https://lore.kernel.org/lkml/20211005184717.65c6d8eb39350395e387b71f@linux-foundation.org Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: kasan-dev@googlegroups.com Signed-off-by: Kees Cook <keescook@chromium.org> --- lib/test_kasan.c | 10 +++++----- lib/test_kasan_module.c | 2 +- 2 files changed, 6 insertions(+), 6 deletions(-)