Hi Kees,
On Tue, Jan 23, 2024 at 1:35 AM Kees Cook <keesc...@chromium.org> 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: 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>
Thanks for your patch!
> --- 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;
"sum" sounds like this is a dummy variable, to please the third
parameter of check_add_overflow()...
> struct vm_area_struct *vma;
>
> /* Check for overflow. */
I agree with Liam: please drop the comment.
> - 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)
... Oh, it is actually used. What about renaming it to "end" instead?
> goto out_unlock;
> }
With the above fixed:
Reviewed-by: Geert Uytterhoeven <ge...@linux-m68k.org>
Acked-by: Geert Uytterhoeven <ge...@linux-m68k.org>
If you want me to take this through the m68k tree (for v6.9), please
let me know.
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
