2021-02-01 17:49:38

by Gustavo A. R. Silva

Subject: [PATCH][next] hv: hyperv.h: Replace one-element array with flexible-array in struct icmsg_negotiate

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member in
struct icmsg_negotiate, instead of a one-element array.

Also, this helps the ongoing efforts to enable -Warray-bounds and fix the
following warnings:

drivers/hv/channel_mgmt.c:315:23: warning: array subscript 1 is above array bounds of ‘struct ic_version[1]’ [-Warray-bounds]
drivers/hv/channel_mgmt.c:316:23: warning: array subscript 1 is above array bounds of ‘struct ic_version[1]’ [-Warray-bounds]

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
include/linux/hyperv.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index f0d48a368f13..7877746f1077 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1528,14 +1528,14 @@ struct icmsg_hdr {
#define IC_VERSION_NEGOTIATION_MAX_VER_COUNT 100
#define ICMSG_HDR (sizeof(struct vmbuspipe_hdr) + sizeof(struct icmsg_hdr))
#define ICMSG_NEGOTIATE_PKT_SIZE(icframe_vercnt, icmsg_vercnt) \
- (ICMSG_HDR + offsetof(struct icmsg_negotiate, icversion_data) + \
+ (ICMSG_HDR + sizeof(struct icmsg_negotiate) + \
(((icframe_vercnt) + (icmsg_vercnt)) * sizeof(struct ic_version)))

struct icmsg_negotiate {
u16 icframe_vercnt;
u16 icmsg_vercnt;
u32 reserved;
- struct ic_version icversion_data[1]; /* any size array */
+ struct ic_version icversion_data[]; /* any size array */
} __packed;

struct shutdown_msg_data {
--
2.27.0

2021-02-01 18:00:14

by Michael Kelley (LINUX)

Subject: RE: [PATCH][next] hv: hyperv.h: Replace one-element array with flexible-array in struct icmsg_negotiate

From: Gustavo A. R. Silva <[email protected]> Sent: Monday, February 1, 2021 9:44 AM
>
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use "flexible array members"[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Refactor the code according to the use of a flexible-array member in
> struct icmsg_negotiate, instead of a one-element array.
>
> Also, this helps the ongoing efforts to enable -Warray-bounds and fix the
> following warnings:
>
> drivers/hv/channel_mgmt.c:315:23: warning: array subscript 1 is above array bounds of 'struct ic_version[1]' [-Warray-bounds]
> drivers/hv/channel_mgmt.c:316:23: warning: array subscript 1 is above array bounds of 'struct ic_version[1]' [-Warray-bounds]
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> include/linux/hyperv.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index f0d48a368f13..7877746f1077 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1528,14 +1528,14 @@ struct icmsg_hdr {
> #define IC_VERSION_NEGOTIATION_MAX_VER_COUNT 100
> #define ICMSG_HDR (sizeof(struct vmbuspipe_hdr) + sizeof(struct icmsg_hdr))
> #define ICMSG_NEGOTIATE_PKT_SIZE(icframe_vercnt, icmsg_vercnt) \
> - (ICMSG_HDR + offsetof(struct icmsg_negotiate, icversion_data) + \
> + (ICMSG_HDR + sizeof(struct icmsg_negotiate) + \
> (((icframe_vercnt) + (icmsg_vercnt)) * sizeof(struct ic_version)))
>
> struct icmsg_negotiate {
> u16 icframe_vercnt;
> u16 icmsg_vercnt;
> u32 reserved;
> - struct ic_version icversion_data[1]; /* any size array */
> + struct ic_version icversion_data[]; /* any size array */
> } __packed;
>
> struct shutdown_msg_data {
> --
> 2.27.0

Reviewed-by: Michael Kelley <[email protected]>

2021-02-01 18:15:51

by Wei Liu

Subject: Re: [PATCH][next] hv: hyperv.h: Replace one-element array with flexible-array in struct icmsg_negotiate

On Mon, Feb 01, 2021 at 05:56:06PM +0000, Michael Kelley wrote:
> From: Gustavo A. R. Silva <[email protected]> Sent: Monday, February 1, 2021 9:44 AM
[...]
> > struct shutdown_msg_data {
> > --
> > 2.27.0
>
> Reviewed-by: Michael Kelley <[email protected]>

Applied to hyperv-next. Thanks.

Wei.