On Tue, Jan 30, 2024 at 06:55:57PM +0000, Lorenzo Stoakes wrote: > On Mon, Jan 22, 2024 at 04:27:08PM -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 unsigned wrap-around addition test to use > > check_add_overflow(), retaining the result for later usage (which removes > > the redundant open-coded addition). This paves the way to enabling the > > unsigned wrap-around sanitizer[2] 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@xxxxxxxxxxxxxxxxxxxx> > > Cc: Uladzislau Rezki <urezki@xxxxxxxxx> > > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> > > Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > > Cc: linux-mm@xxxxxxxxx > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > mm/vmalloc.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index d12a17fc0c17..7932ac99e9d3 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1223,6 +1223,7 @@ is_within_this_va(struct vmap_area *va, unsigned long size, > > unsigned long align, unsigned long vstart) > > { > > unsigned long nva_start_addr; > > + unsigned long sum; > > > > if (va->va_start > vstart) > > nva_start_addr = ALIGN(va->va_start, align); > > @@ -1230,11 +1231,11 @@ is_within_this_va(struct vmap_area *va, unsigned long size, > > nva_start_addr = ALIGN(vstart, align); > > > > /* Can be overflowed due to big size or alignment. */ > > - if (nva_start_addr + size < nva_start_addr || > > + if (check_add_overflow(nva_start_addr, size, &sum) || > > nva_start_addr < vstart) > > return false; > > > > - return (nva_start_addr + size <= va->va_end); > > + return (sum <= va->va_end); > > } > > > > /* > > -- > > 2.34.1 > > > > Looks good to me, > > Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > Same here. One small nit though. The "sum" variable is not something that it suits for. IMO, we should use a better name and replace it: "nva_offset"? -- Uladzislau Rezki
