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Message-ID: <2efb1f4751fa47380d51ce538253983974a4947c.camel@mediatek.com>
Date: Thu, 29 Aug 2024 12:44:53 +0000
From: Tze-nan Wu (吳澤南) <Tze-nan.Wu@...iatek.com>
To: "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
"sdf@...ichev.me" <sdf@...ichev.me>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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<yonghong.song@...ux.dev>, "haoluo@...gle.com" <haoluo@...gle.com>
Subject: Re: [PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in
do_sock_getsockopt()
On Fri, 2024-08-23 at 19:04 -0700, Stanislav Fomichev wrote:
>
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
> On 08/22, Alexei Starovoitov wrote:
> > On Thu, Aug 22, 2024 at 12:02 AM Tze-nan Wu (吳澤南)
> > <Tze-nan.Wu@...iatek.com> wrote:
> > >
> > >
> > > BTW, If this should be handled in kernel, modification shown
> below
> > > could fix the issue without breaking the "static_branch" usage in
> both
> > > macros:
> > >
> > >
> > > +++ /include/linux/bpf-cgroup.h:
> > > -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen)
> > > +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, compat)
> > > ({
> > > int __ret = 0;
> > > if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))
> > > copy_from_sockptr(&__ret, optlen, sizeof(int));
> > > + else
> > > + *compat = true;
> > > __ret;
> > > })
> > >
> > > #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname,
> > > optval, optlen, max_optlen, retval)
> > > ({
> > > int __ret = retval;
> > > - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) &&
> > > - cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))
> > > + if (cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))
> > > if (!(sock)->sk_prot->bpf_bypass_getsockopt ||
> > > ...
> > >
> > > +++ /net/socket.c:
> > > int do_sock_getsockopt(struct socket *sock, bool compat, int
> level,
> > > {
> > > ...
> > > ...
> > > + /* The meaning of `compat` variable could be changed
> here
> > > + * to indicate if cgroup_bpf_enabled(CGROUP_SOCK_OPS)
> is
> > > false.
> > > + */
> > > if (!compat)
> > > - max_optlen =
> BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> > > + max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen,
> > > &compat);
> >
> > This is better, but it's still quite a hack. Let's not override it.
> > We can have another bool, but the question:
> > do we really need BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN ?
> > copy_from_sockptr(&__ret, optlen, sizeof(int));
> > should be fast enough to do it unconditionally.
> > What are we saving here?
> >
> > Stan ?
>
> Agreed, most likely nobody would notice :-)
Sorry for my late reply, just have the mailer fixed.
If it is feasible to make the `copy_from_sockptr` unconditionally,
should I submit a new patch that resolve the issue by removing
`BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`? Patch A shown as below.
+++ /net/socket.c:
int do_sock_getsockopt(...)
{
- int max_optlen __maybe_unused;
+ int max_optlen __maybe_unused = 0;
const struct proto_ops *ops;
int err;
...
...
if (!compat) <== wonder if we should keep the condition here?
- max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
+ copy_from_sockptr(&max_optlen, optlen, sizeof(int));
ops = READ_ONCE(sock->ops);
if (level == SOL_SOCKET) {
-----------------------------------------
Or perhaps adding another variable "enabled" is the preferable way?
As it keeps the static_branch behavior.
Patch B shown as below:
+++ /include/linux/bpf-cgroup.h:
-#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen)
+#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled)
({
int __ret = 0;
if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))
copy_from_sockptr(&__ret, optlen, sizeof(int));
+ else
+ *enabled = false;
__ret;
})
+++ /net/socket.c:
int do_sock_getsockopt(...)
{
+ bool enabled __maybe_unused = !compat;
int max_optlen __maybe_unused;
const struct proto_ops *ops;
int err;
if (!compat)
- max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
+ max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen,
&enabled);
ops = READ_ONCE(sock->ops);
...
...
- if (!compat)
+ if (enabled)
err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(...);
-----------------------------------------
Any comments would be appreciated.
--Tze-nan
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