* Kees Cook <keesc...@chromium.org> [240122 19:36]: > 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: Geert Uytterhoeven <ge...@linux-m68k.org> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Arnd Bergmann <a...@arndb.de> > Cc: Liam Howlett <liam.howl...@oracle.com> > Cc: "Matthew Wilcox (Oracle)" <wi...@infradead.org> > Cc: Hugh Dickins <hu...@google.com> > Cc: linux-m...@lists.linux-m68k.org > Signed-off-by: Kees Cook <keesc...@chromium.org> > --- > arch/m68k/kernel/sys_m68k.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c > index 1af5e6082467..b2b9248f2566 100644 > --- a/arch/m68k/kernel/sys_m68k.c > +++ b/arch/m68k/kernel/sys_m68k.c > @@ -391,10 +391,11 @@ sys_cacheflush (unsigned long addr, int scope, int > cache, unsigned long len) > > mmap_read_lock(current->mm); > } else { > + unsigned long sum; > struct vm_area_struct *vma; > > /* Check for overflow. */
With your nice self-documenting code, you can probably drop that comment. With or without the change, Reviewed-by: Liam R. Howlett <liam.howl...@oracle.com> > - if (addr + len < addr) > + if (check_add_overflow(addr, len, &sum)) > goto out; > > /* > @@ -403,7 +404,7 @@ sys_cacheflush (unsigned long addr, int scope, int cache, > unsigned long len) > */ > mmap_read_lock(current->mm); > vma = vma_lookup(current->mm, addr); > - if (!vma || addr + len > vma->vm_end) > + if (!vma || sum > vma->vm_end) > goto out_unlock; > } > > -- > 2.34.1 >
