| Message ID | c8e93571c18b3528aac5eb33ade213bf133d10ad.1613692950.git.andreyknvl@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] kasan: initialize shadow to TAG_INVALID for SW_TAGS | expand |
On Fri, Feb 19, 2021 at 1:22 AM Andrey Konovalov <andreyknvl@google.com> wrote: > > Currently, KASAN_SW_TAGS uses 0xFF as the default tag value for > unallocated memory. The underlying idea is that since that memory > hasn't been allocated yet, it's only supposed to be dereferenced > through a pointer with the native 0xFF tag. > > While this is a good idea in terms on consistency, practically it > doesn't bring any benefit. Since the 0xFF pointer tag is a match-all > tag, it doesn't matter what tag the accessed memory has. No accesses > through 0xFF-tagged pointers are considered buggy by KASAN. > > This patch changes the default tag value for unallocated memory to 0xFE, > which is the tag KASAN uses for inaccessible memory. This doesn't affect > accesses through 0xFF-tagged pointer to this memory, but this allows > KASAN to detect wild and large out-of-bounds invalid memory accesses > through otherwise-tagged pointers. > > This is a prepatory patch for the next one, which changes the tag-based > KASAN modes to not poison the boot memory. > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > --- > include/linux/kasan.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h > index 14f72ec96492..44c147dae7e3 100644 > --- a/include/linux/kasan.h > +++ b/include/linux/kasan.h > @@ -30,7 +30,8 @@ struct kunit_kasan_expectation { > /* Software KASAN implementations use shadow memory. */ > > #ifdef CONFIG_KASAN_SW_TAGS > -#define KASAN_SHADOW_INIT 0xFF > +/* This matches KASAN_TAG_INVALID. */ > +#define KASAN_SHADOW_INIT 0xFE > #else > #define KASAN_SHADOW_INIT 0 > #endif > -- > 2.30.0.617.g56c4b15f3c-goog > Hi Andrew, Could you pick up this series into mm? The discussion on v1 of this series was hijacked discussing an unrelated issue. Thanks!
diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 14f72ec96492..44c147dae7e3 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -30,7 +30,8 @@ struct kunit_kasan_expectation { /* Software KASAN implementations use shadow memory. */ #ifdef CONFIG_KASAN_SW_TAGS -#define KASAN_SHADOW_INIT 0xFF +/* This matches KASAN_TAG_INVALID. */ +#define KASAN_SHADOW_INIT 0xFE #else #define KASAN_SHADOW_INIT 0 #endif
Currently, KASAN_SW_TAGS uses 0xFF as the default tag value for unallocated memory. The underlying idea is that since that memory hasn't been allocated yet, it's only supposed to be dereferenced through a pointer with the native 0xFF tag. While this is a good idea in terms on consistency, practically it doesn't bring any benefit. Since the 0xFF pointer tag is a match-all tag, it doesn't matter what tag the accessed memory has. No accesses through 0xFF-tagged pointers are considered buggy by KASAN. This patch changes the default tag value for unallocated memory to 0xFE, which is the tag KASAN uses for inaccessible memory. This doesn't affect accesses through 0xFF-tagged pointer to this memory, but this allows KASAN to detect wild and large out-of-bounds invalid memory accesses through otherwise-tagged pointers. This is a prepatory patch for the next one, which changes the tag-based KASAN modes to not poison the boot memory. Signed-off-by: Andrey Konovalov <andreyknvl@google.com> --- include/linux/kasan.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)