| Message ID | 20240123002814.1396804-78-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
On Mon, Jan 22, 2024 at 04:27:53PM -0800, Kees Cook wrote: > In an effort to separate intentional arithmetic wrap-around from > unexpected wrap-around, we need to refactor places that depend on this > kind of math. One of the most common code patterns of this is: > > VAR + value < VAR > > Notably, this is considered "undefined behavior" for signed and pointer > types, which the kernel works around by using the -fno-strict-overflow > option in the build[1] (which used to just be -fwrapv). Regardless, we > want to get the kernel source to the position where we can meaningfully > instrument arithmetic wrap-around conditions and catch them when they > are unexpected, regardless of whether they are signed[2], unsigned[3], > or pointer[4] types. > > Refactor open-coded wrap-around addition test to use add_would_overflow(). > This paves the way to enabling the wrap-around sanitizers in the future. > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > Link: https://github.com/KSPP/linux/issues/26 [2] > Link: https://github.com/KSPP/linux/issues/27 [3] > Link: https://github.com/KSPP/linux/issues/344 [4] > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Uladzislau Rezki <urezki@gmail.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Lorenzo Stoakes <lstoakes@gmail.com> > Cc: linux-mm@kvack.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > mm/vmalloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 7932ac99e9d3..3d73f2ac6957 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3750,7 +3750,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) > addr = kasan_reset_tag(addr); > > /* Don't allow overflow */ > - if ((unsigned long) addr + count < count) > + if (add_would_overflow(count, (unsigned long)addr)) > count = -(unsigned long) addr; > > remains = count; > -- > 2.34.1 > Looks good to me, Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 7932ac99e9d3..3d73f2ac6957 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -3750,7 +3750,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count) addr = kasan_reset_tag(addr); /* Don't allow overflow */ - if ((unsigned long) addr + count < count) + if (add_would_overflow(count, (unsigned long)addr)) count = -(unsigned long) addr; remains = count;
In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded wrap-around addition test to use add_would_overflow(). This paves the way to enabling the wrap-around sanitizers in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Uladzislau Rezki <urezki@gmail.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: linux-mm@kvack.org Signed-off-by: Kees Cook <keescook@chromium.org> --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)