diff mbox series

[80/82] xen-netback: Refactor intentional wrap-around test

Message ID 20240123002814.1396804-80-keescook@chromium.org (mailing list archive)
State Changes Requested
Headers show
Series overflow: Refactor open-coded arithmetic wrap-around | expand

Commit Message

Kees Cook Jan. 23, 2024, 12:27 a.m. UTC 
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: Wei Liu <wei.liu@kernel.org>
Cc: Paul Durrant <paul@xen.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: xen-devel@lists.xenproject.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/xen-netback/hash.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Jan Beulich Jan. 23, 2024, 7:55 a.m. UTC | #1 
On 23.01.2024 01:27, Kees Cook wrote:
> --- a/drivers/net/xen-netback/hash.c
> +++ b/drivers/net/xen-netback/hash.c
> @@ -345,7 +345,7 @@ u32 xenvif_set_hash_mapping(struct xenvif *vif, u32 gref, u32 len,
>  		.flags = GNTCOPY_source_gref
>  	}};
>  
> -	if ((off + len < off) || (off + len > vif->hash.size) ||
> +	if ((add_would_overflow(off, len)) || (off + len > vif->hash.size) ||

I'm not maintainer of this code, but if I was I would ask that the
excess parentheses be removed, to improve readability.

Jan
Kees Cook Jan. 23, 2024, 9:32 p.m. UTC | #2 
On Tue, Jan 23, 2024 at 08:55:44AM +0100, Jan Beulich wrote:
> On 23.01.2024 01:27, Kees Cook wrote:
> > --- a/drivers/net/xen-netback/hash.c
> > +++ b/drivers/net/xen-netback/hash.c
> > @@ -345,7 +345,7 @@ u32 xenvif_set_hash_mapping(struct xenvif *vif, u32 gref, u32 len,
> >  		.flags = GNTCOPY_source_gref
> >  	}};
> >  
> > -	if ((off + len < off) || (off + len > vif->hash.size) ||
> > +	if ((add_would_overflow(off, len)) || (off + len > vif->hash.size) ||
> 
> I'm not maintainer of this code, but if I was I would ask that the
> excess parentheses be removed, to improve readability.

Good call. I will adjust that. Thanks!

-Kees
diff mbox series

Patch

diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c
index ff96f22648ef..69b03b4feba9 100644
--- a/drivers/net/xen-netback/hash.c
+++ b/drivers/net/xen-netback/hash.c
@@ -345,7 +345,7 @@  u32 xenvif_set_hash_mapping(struct xenvif *vif, u32 gref, u32 len,
 		.flags = GNTCOPY_source_gref
 	}};
 
-	if ((off + len < off) || (off + len > vif->hash.size) ||
+	if ((add_would_overflow(off, len)) || (off + len > vif->hash.size) ||
 	    len > XEN_PAGE_SIZE / sizeof(*mapping))
 		return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;