On Fri, May 7, 2021 at 1:47 AM Peter Collingbourne <pcc@xxxxxxxxxx> wrote: > > On Thu, May 6, 2021 at 3:12 PM Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: > > > > On Thu, May 6, 2021 at 11:20 PM Peter Collingbourne <pcc@xxxxxxxxxx> wrote: > > > > > > These tests deliberately access these arrays out of bounds, > > > which will cause the dynamic local bounds checks inserted by > > > CONFIG_UBSAN_LOCAL_BOUNDS to fail and panic the kernel. To avoid this > > > problem, access the arrays via volatile pointers, which will prevent > > > the compiler from being able to determine the array bounds. > > > > > > Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> > > > Cc: stable@xxxxxxxxxxxxxxx > > > Link: https://linux-review.googlesource.com/id/I90b1713fbfa1bf68ff895aef099ea77b98a7c3b9 > > > --- > > > lib/test_kasan.c | 14 ++++++++------ > > > 1 file changed, 8 insertions(+), 6 deletions(-) > > > > > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > > > index dc05cfc2d12f..2a078e8e7b8e 100644 > > > --- a/lib/test_kasan.c > > > +++ b/lib/test_kasan.c > > > @@ -654,8 +654,8 @@ static char global_array[10]; > > > > > > static void kasan_global_oob(struct kunit *test) > > > { > > > - volatile int i = 3; > > > - char *p = &global_array[ARRAY_SIZE(global_array) + i]; > > > + char *volatile array = global_array; > > > + char *p = &array[ARRAY_SIZE(global_array) + 3]; > > > > Nit: in the kernel, "volatile" usually comes before the pointer type. > > That would refer to a different type. "volatile char *" is a pointer > to volatile char, while "char *volatile" is a volatile pointer to > char. The latter is what we want here, because we want to prevent the > compiler from inferring things about the pointer itself (i.e. its > array bounds), not the data that it refers to. I see. This is unusual. I'd say this needs to be explicitly explained in the commit message, as well as in a comment in the code.
