On 2/28/24 18:01, Kees Cook wrote:
On Wed, Feb 28, 2024 at 02:41:48PM -0800, Jakub Kicinski wrote:
On Wed, 28 Feb 2024 13:46:10 -0800 Kees Cook wrote:
I really don't like hiding these trailing allocations from the compiler.
Why can't something like this be done (totally untested):
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 118c40258d07..dae6df4fb177 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2475,6 +2475,8 @@ struct net_device {
/** @page_pools: page pools created for this netdevice */
struct hlist_head page_pools;
#endif
+ u32 priv_size;
+ u8 priv_data[] __counted_by(priv_size)
__aligned(NETDEV_ALIGN);
I like, FWIW, please submit! :)
So, I found several cases where struct net_device is included in the
middle of another structure, which makes my proposal more awkward. But I
also don't understand why it's in the _middle_. Shouldn't it always be
at the beginning (with priv stuff following it?)
Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'
struct rtw89_dev
struct ath10k
etc.
Some even have two included (?)
But I still like the idea -- Gustavo has been solving these cases with
having two structs, e.g.:
struct net_device {
...unchanged...
};
struct net_device_alloc {
struct net_device dev;
u32 priv_size;
u8 priv_data[] __counted_by(priv_size)
__aligned(NETDEV_ALIGN);
};
And internals can use struct net_device_alloc...
Yep, we should really consider going with the above, otherwise we would
have to do something like the following, to avoid having the flexible-array
member nested in the middle of other structs:
struct net_device {
struct_group_tagged(net_device_hdr, hdr,
...
u32 priv_size;
);
u8 priv_data[] __counted_by(priv_size)
__aligned(NETDEV_ALIGN);
}
We are grouping together the members in `struct net_device`, except the
flexible-array member, into a tagged `struct net_device_hdr`. This allows
us to exclude the flex array from its inclusion in any other struct
that contains `struct net_device` as a member without having to create
a completely separate struct definition.
And let's take as example `struct hfi1_netdev_rx`, where `struct net_device` is
included in the beginning:
drivers/infiniband/hw/hfi1/netdev.h:
struct hfi1_netdev_rx {
- struct net_device rx_napi;
+ struct net_device_hdr rx_napi;
struct hfi1_devdata *dd;
struct hfi1_netdev_rxq *rxq;
int num_rx_q;
int rmt_start;
struct xarray dev_tbl;
/* count of enabled napi polls */
atomic_t enabled;
/* count of netdevs on top */
atomic_t netdevs;
};
Of course we would also have to update the code that access `struct net_device`
members through `rx_napi` in `struct hfi1_netdev_rx`.
I'm currently working on the above solution for all the cases where having two
separate structs is not currently feasible. And with that we are looking to
enable
`-Wflex-array-member-not-at-end`
So, if we can prevent this from the beginning it'd be really great. :)
--
Gustavo
