[RFC PATCH bpf-next 0/7] bpf: Implement BPF_LINK_UPDATE for tracing links

[RFC PATCH bpf-next 0/7] bpf: Implement BPF_LINK_UPDATE for tracing links

[Jordan Rife]

Implement update_prog for bpf_tracing_link_lops to enable
BPF_LINK_UPDATE for fentry, fexit, fmod_ret, freplace, etc. links.

My initial motivation for this was to enable a use case where one
process creates and owns links pointing to "hooks" within a tc, xdp, ...
attachment and an external "plugin" loads freplace programs and updates
links to these hooks. Aside from that though, it seemed like it could
be useful to be able to atomically swap out the program associated with
an freplace/fentry/fexit/fmod_ret link more generally.

Implementing program updates for freplace links was fairly
straightforward but proved more difficult for the other link types. The
third patch in this series discusses some other approaches I considered
before settling on the current approach, but I'd appreciate others'
input here to see if there is a better way to implement this that
doesn't require architecture-specific changes.

Thanks!

Jordan

Jordan Rife (7):
  bpf: Set up update_prog scaffolding for bpf_tracing_link_lops
  bpf: Enable BPF_LINK_UPDATE for freplace links
  bpf: Enable BPF_LINK_UPDATE for fentry/fexit/fmod_ret links
  bpf, x86: Make program update work for trampoline ops
  bpf, s390: Make program update work for trampoline ops
  bpf, arm64: Make program update work for trampoline ops
  selftests/bpf: Test BPF_LINK_UPDATE behavior for tracing links

 arch/arm64/net/bpf_jit_comp.c                 |  23 +-
 arch/s390/net/bpf_jit_comp.c                  |  24 +-
 arch/x86/net/bpf_jit_comp.c                   |  17 +-
 include/linux/bpf.h                           |  21 +
 kernel/bpf/syscall.c                          |  68 +++
 kernel/bpf/trampoline.c                       |  75 ++-
 .../bpf/prog_tests/prog_update_tracing.c      | 460 ++++++++++++++++++
 .../selftests/bpf/progs/prog_update_tracing.c | 133 +++++
 8 files changed, 796 insertions(+), 25 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/prog_update_tracing.c
 create mode 100644 tools/testing/selftests/bpf/progs/prog_update_tracing.c

-- 
2.43.0

[RFC PATCH bpf-next 1/7] bpf: Set up update_prog scaffolding for bpf_tracing_link_lops

[Jordan Rife]

The type and expected_attach_type of the new program must match the
original program and the new program must be compatible with the
attachment target. Use a global mutex, trace_link_mutex, to synchronize
parallel update operations similar to other link types (sock_map, xdp,
etc.) that use a global mutex. Contention should be low, so this should
be OK. Subsequent patches fill in the program update logic for
freplace/fentry/fmod_ret/fexit links.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 include/linux/bpf.h     | 11 +++++++
 kernel/bpf/syscall.c    | 68 +++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/trampoline.c | 29 ++++++++++++++++++
 3 files changed, 108 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 09d5dc541d1c..23fcbcd26aa4 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1420,6 +1420,9 @@ static inline int bpf_dynptr_check_off_len(const struct bpf_dynptr_kern *ptr, u6
 int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 			     struct bpf_trampoline *tr,
 			     struct bpf_prog *tgt_prog);
+int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
+			       struct bpf_prog *new_prog,
+			       struct bpf_trampoline *tr);
 int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 			       struct bpf_trampoline *tr,
 			       struct bpf_prog *tgt_prog);
@@ -1509,6 +1512,14 @@ static inline int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 {
 	return -ENOTSUPP;
 }
+
+static inline int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
+					     struct bpf_prog *new_prog,
+					     struct bpf_trampoline *tr)
+{
+	return -ENOTSUPP;
+}
+
 static inline int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 					     struct bpf_trampoline *tr,
 					     struct bpf_prog *tgt_prog)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f62d61b6730a..b0da7c428a65 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -63,6 +63,8 @@ static DEFINE_IDR(map_idr);
 static DEFINE_SPINLOCK(map_idr_lock);
 static DEFINE_IDR(link_idr);
 static DEFINE_SPINLOCK(link_idr_lock);
+/* Synchronizes access to prog between link update operations. */
+static DEFINE_MUTEX(trace_link_mutex);
 
 int sysctl_unprivileged_bpf_disabled __read_mostly =
 	IS_BUILTIN(CONFIG_BPF_UNPRIV_DEFAULT_OFF) ? 2 : 0;
@@ -3562,11 +3564,77 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
 	return 0;
 }
 
+static int bpf_tracing_link_update_prog(struct bpf_link *link,
+					struct bpf_prog *new_prog,
+					struct bpf_prog *old_prog)
+{
+	struct bpf_tracing_link *tr_link =
+		container_of(link, struct bpf_tracing_link, link.link);
+	struct bpf_attach_target_info tgt_info = {0};
+	int err = 0;
+	u32 btf_id;
+
+	mutex_lock(&trace_link_mutex);
+
+	if (old_prog && link->prog != old_prog) {
+		err = -EPERM;
+		goto out;
+	}
+	old_prog = link->prog;
+	if (old_prog->type != new_prog->type ||
+	    old_prog->expected_attach_type != new_prog->expected_attach_type) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	mutex_lock(&new_prog->aux->dst_mutex);
+
+	if (!new_prog->aux->dst_trampoline ||
+	    new_prog->aux->dst_trampoline->key != tr_link->trampoline->key) {
+		bpf_trampoline_unpack_key(tr_link->trampoline->key, NULL,
+					  &btf_id);
+		/* If there is no saved target, or the target associated with
+		 * this link is different from the destination specified at
+		 * load time, we need to check for compatibility.
+		 */
+		err = bpf_check_attach_target(NULL, new_prog, tr_link->tgt_prog,
+					      btf_id, &tgt_info);
+		if (err)
+			goto out_unlock;
+	}
+
+	err = bpf_trampoline_update_prog(&tr_link->link, new_prog,
+					 tr_link->trampoline);
+	if (err)
+		goto out_unlock;
+
+	/* Clear the trampoline, mod, and target prog from new_prog->aux to make
+	 * sure the original attach destination is not kept alive after a
+	 * program is (re-)attached to another target.
+	 */
+	if (new_prog->aux->dst_prog)
+		bpf_prog_put(new_prog->aux->dst_prog);
+	bpf_trampoline_put(new_prog->aux->dst_trampoline);
+	module_put(new_prog->aux->mod);
+
+	new_prog->aux->dst_prog = NULL;
+	new_prog->aux->dst_trampoline = NULL;
+	new_prog->aux->mod = tgt_info.tgt_mod;
+	tgt_info.tgt_mod = NULL; /* Make module_put() below do nothing. */
+out_unlock:
+	mutex_unlock(&new_prog->aux->dst_mutex);
+out:
+	mutex_unlock(&trace_link_mutex);
+	module_put(tgt_info.tgt_mod);
+	return err;
+}
+
 static const struct bpf_link_ops bpf_tracing_link_lops = {
 	.release = bpf_tracing_link_release,
 	.dealloc = bpf_tracing_link_dealloc,
 	.show_fdinfo = bpf_tracing_link_show_fdinfo,
 	.fill_link_info = bpf_tracing_link_fill_link_info,
+	.update_prog = bpf_tracing_link_update_prog,
 };
 
 static int bpf_tracing_prog_attach(struct bpf_prog *prog,
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 5949095e51c3..010bcba0db65 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -610,6 +610,35 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 	return err;
 }
 
+static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
+					struct bpf_prog *new_prog,
+					struct bpf_trampoline *tr)
+{
+	return -ENOTSUPP;
+}
+
+int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
+			       struct bpf_prog *new_prog,
+			       struct bpf_trampoline *tr)
+{
+	struct bpf_prog *old_prog;
+	int err;
+
+	mutex_lock(&tr->mutex);
+	err = __bpf_trampoline_update_prog(link, new_prog, tr);
+	if (!err) {
+		/* If a program update was successful, switch the program
+		 * in the link before releasing tr->mutex; otherwise, another
+		 * operation could come along and update the trampoline with
+		 * the link still pointing at the old program.
+		 */
+		old_prog = xchg(&link->link.prog, new_prog);
+		bpf_prog_put(old_prog);
+	}
+	mutex_unlock(&tr->mutex);
+	return err;
+}
+
 static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 					struct bpf_trampoline *tr,
 					struct bpf_prog *tgt_prog)
-- 
2.43.0

Re: [RFC PATCH bpf-next 1/7] bpf: Set up update_prog scaffolding for bpf_tracing_link_lops

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 2543 bytes --]

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 09d5dc541..23fcbcd26 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h

[ ... ]

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a2a441185..14dd8be7b 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c

[ ... ]

> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 04104397c..d2fd02e10 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -607,6 +607,35 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
>  	return err;
>  }
>
> +static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
> +					struct bpf_prog *new_prog,
> +					struct bpf_trampoline *tr)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
> +			       struct bpf_prog *new_prog,
> +			       struct bpf_trampoline *tr)
> +{
> +	struct bpf_prog *old_prog;
> +	int err;
> +
> +	mutex_lock(&tr->mutex);
> +	err = __bpf_trampoline_update_prog(link, new_prog, tr);
> +	if (!err) {
> +		/* If a program update was successful, switch the program
> +		 * in the link before releasing tr->mutex; otherwise, another
> +		 * operation could come along and update the trampoline with
> +		 * the link still pointing at the old program.
> +		 */
> +		old_prog = xchg(&link->link.prog, new_prog);
> +		bpf_prog_put(old_prog);
> +	}
> +	mutex_unlock(&tr->mutex);
> +	return err;
> +}
> +

Can bpf_prog_put() be called while holding tr->mutex?

When bpf_prog_put()->__bpf_prog_put() drops the program's refcount to
zero and we're not in IRQ context (which we aren't when holding a regular
mutex), it directly calls bpf_prog_put_deferred(). This eventually calls
bpf_trampoline_put(), which takes trampoline_mutex.

The existing code in bpf_trampoline_link_cgroup_shim() carefully unlocks
tr->mutex before calling bpf_trampoline_put() (see the comment "have to
release tr while _not_ holding its mutex"). Additionally,
bpf_trampoline_put() has WARN_ON_ONCE(mutex_is_locked(&tr->mutex)) to
catch this pattern.

Should bpf_prog_put() be moved after mutex_unlock(&tr->mutex)?

>  static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
>  					struct bpf_trampoline *tr,
>  					struct bpf_prog *tgt_prog)

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19450205468

Re: [RFC PATCH bpf-next 1/7] bpf: Set up update_prog scaffolding for bpf_tracing_link_lops

[Jordan Rife]

On Tue, Nov 18, 2025 at 01:27:45AM +0000, bot+bpf-ci@kernel.org wrote:
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 09d5dc541..23fcbcd26 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> 
> [ ... ]
> 
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index a2a441185..14dd8be7b 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> 
> [ ... ]
> 
> > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> > index 04104397c..d2fd02e10 100644
> > --- a/kernel/bpf/trampoline.c
> > +++ b/kernel/bpf/trampoline.c
> > @@ -607,6 +607,35 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
> >  	return err;
> >  }
> >
> > +static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
> > +					struct bpf_prog *new_prog,
> > +					struct bpf_trampoline *tr)
> > +{
> > +	return -ENOTSUPP;
> > +}
> > +
> > +int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
> > +			       struct bpf_prog *new_prog,
> > +			       struct bpf_trampoline *tr)
> > +{
> > +	struct bpf_prog *old_prog;
> > +	int err;
> > +
> > +	mutex_lock(&tr->mutex);
> > +	err = __bpf_trampoline_update_prog(link, new_prog, tr);
> > +	if (!err) {
> > +		/* If a program update was successful, switch the program
> > +		 * in the link before releasing tr->mutex; otherwise, another
> > +		 * operation could come along and update the trampoline with
> > +		 * the link still pointing at the old program.
> > +		 */
> > +		old_prog = xchg(&link->link.prog, new_prog);
> > +		bpf_prog_put(old_prog);
> > +	}
> > +	mutex_unlock(&tr->mutex);
> > +	return err;
> > +}
> > +
> 
> Can bpf_prog_put() be called while holding tr->mutex?
> 
> When bpf_prog_put()->__bpf_prog_put() drops the program's refcount to
> zero and we're not in IRQ context (which we aren't when holding a regular
> mutex), it directly calls bpf_prog_put_deferred(). This eventually calls
> bpf_trampoline_put(), which takes trampoline_mutex.

The only code path I see where this is true is where
bpf_prog_put_deferred may eventually lead to this line in
bpf_prog_free_deferred:

	if (aux->dst_trampoline)
		bpf_trampoline_put(aux->dst_trampoline);

In this case though aux->dst_trampoline would have been cleared in
bpf_tracing_link_update_prog or bpf_tracing_prog_attach so this code
path wouldn't run.

> The existing code in bpf_trampoline_link_cgroup_shim() carefully unlocks
> tr->mutex before calling bpf_trampoline_put() (see the comment "have to
> release tr while _not_ holding its mutex"). Additionally,
> bpf_trampoline_put() has WARN_ON_ONCE(mutex_is_locked(&tr->mutex)) to
> catch this pattern.
> 
> Should bpf_prog_put() be moved after mutex_unlock(&tr->mutex)?

I don't see how a deadlock could occur in this scenario, but I could
move it after mutex_unlock() to remove any doubt.
 
> >  static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
> >  					struct bpf_trampoline *tr,
> >  					struct bpf_prog *tgt_prog)
> 
> [ ... ]
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19450205468

Re: [RFC PATCH bpf-next 1/7] bpf: Set up update_prog scaffolding for bpf_tracing_link_lops

[Jiri Olsa]

On Mon, Nov 17, 2025 at 04:52:53PM -0800, Jordan Rife wrote:

SNIP

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index f62d61b6730a..b0da7c428a65 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -63,6 +63,8 @@ static DEFINE_IDR(map_idr);
>  static DEFINE_SPINLOCK(map_idr_lock);
>  static DEFINE_IDR(link_idr);
>  static DEFINE_SPINLOCK(link_idr_lock);
> +/* Synchronizes access to prog between link update operations. */
> +static DEFINE_MUTEX(trace_link_mutex);
>  
>  int sysctl_unprivileged_bpf_disabled __read_mostly =
>  	IS_BUILTIN(CONFIG_BPF_UNPRIV_DEFAULT_OFF) ? 2 : 0;
> @@ -3562,11 +3564,77 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
>  	return 0;
>  }
>  
> +static int bpf_tracing_link_update_prog(struct bpf_link *link,
> +					struct bpf_prog *new_prog,
> +					struct bpf_prog *old_prog)
> +{
> +	struct bpf_tracing_link *tr_link =
> +		container_of(link, struct bpf_tracing_link, link.link);
> +	struct bpf_attach_target_info tgt_info = {0};
> +	int err = 0;
> +	u32 btf_id;
> +
> +	mutex_lock(&trace_link_mutex);

that seems too much, we could add link->mutex

> +
> +	if (old_prog && link->prog != old_prog) {
> +		err = -EPERM;
> +		goto out;
> +	}
> +	old_prog = link->prog;
> +	if (old_prog->type != new_prog->type ||
> +	    old_prog->expected_attach_type != new_prog->expected_attach_type) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	mutex_lock(&new_prog->aux->dst_mutex);
> +
> +	if (!new_prog->aux->dst_trampoline ||
> +	    new_prog->aux->dst_trampoline->key != tr_link->trampoline->key) {

hum, would be easier (and still usefull) to allow just programs for the same function?

> +		bpf_trampoline_unpack_key(tr_link->trampoline->key, NULL,
> +					  &btf_id);
> +		/* If there is no saved target, or the target associated with
> +		 * this link is different from the destination specified at
> +		 * load time, we need to check for compatibility.
> +		 */
> +		err = bpf_check_attach_target(NULL, new_prog, tr_link->tgt_prog,
> +					      btf_id, &tgt_info);
> +		if (err)
> +			goto out_unlock;
> +	}
> +
> +	err = bpf_trampoline_update_prog(&tr_link->link, new_prog,
> +					 tr_link->trampoline);
> +	if (err)
> +		goto out_unlock;
> +
> +	/* Clear the trampoline, mod, and target prog from new_prog->aux to make
> +	 * sure the original attach destination is not kept alive after a
> +	 * program is (re-)attached to another target.
> +	 */
> +	if (new_prog->aux->dst_prog)
> +		bpf_prog_put(new_prog->aux->dst_prog);
> +	bpf_trampoline_put(new_prog->aux->dst_trampoline);

would it be possible just to take tr->mutex and unlink/link
the programs, something like:

        mutex_lock(&tr->mutex);

	__bpf_trampoline_unlink_prog(old_prog)
	__bpf_trampoline_link_prog(new_prog)

        mutex_unlock(&tr->mutex);

I might be missing something but this way we wouldn't need
the arch chages in the following patches?


jirka


> +	module_put(new_prog->aux->mod);
> +
> +	new_prog->aux->dst_prog = NULL;
> +	new_prog->aux->dst_trampoline = NULL;
> +	new_prog->aux->mod = tgt_info.tgt_mod;
> +	tgt_info.tgt_mod = NULL; /* Make module_put() below do nothing. */
> +out_unlock:
> +	mutex_unlock(&new_prog->aux->dst_mutex);
> +out:
> +	mutex_unlock(&trace_link_mutex);
> +	module_put(tgt_info.tgt_mod);
> +	return err;
> +}
> +
>  static const struct bpf_link_ops bpf_tracing_link_lops = {
>  	.release = bpf_tracing_link_release,
>  	.dealloc = bpf_tracing_link_dealloc,
>  	.show_fdinfo = bpf_tracing_link_show_fdinfo,
>  	.fill_link_info = bpf_tracing_link_fill_link_info,
> +	.update_prog = bpf_tracing_link_update_prog,
>  };
>  

SNIP

Re: [RFC PATCH bpf-next 1/7] bpf: Set up update_prog scaffolding for bpf_tracing_link_lops

[Jordan Rife]

On Fri, Nov 21, 2025 at 05:34:54PM +0100, Jiri Olsa wrote:
> On Mon, Nov 17, 2025 at 04:52:53PM -0800, Jordan Rife wrote:
> 
> SNIP
> 
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index f62d61b6730a..b0da7c428a65 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -63,6 +63,8 @@ static DEFINE_IDR(map_idr);
> >  static DEFINE_SPINLOCK(map_idr_lock);
> >  static DEFINE_IDR(link_idr);
> >  static DEFINE_SPINLOCK(link_idr_lock);
> > +/* Synchronizes access to prog between link update operations. */
> > +static DEFINE_MUTEX(trace_link_mutex);
> >  
> >  int sysctl_unprivileged_bpf_disabled __read_mostly =
> >  	IS_BUILTIN(CONFIG_BPF_UNPRIV_DEFAULT_OFF) ? 2 : 0;
> > @@ -3562,11 +3564,77 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
> >  	return 0;
> >  }
> >  
> > +static int bpf_tracing_link_update_prog(struct bpf_link *link,
> > +					struct bpf_prog *new_prog,
> > +					struct bpf_prog *old_prog)
> > +{
> > +	struct bpf_tracing_link *tr_link =
> > +		container_of(link, struct bpf_tracing_link, link.link);
> > +	struct bpf_attach_target_info tgt_info = {0};
> > +	int err = 0;
> > +	u32 btf_id;
> > +
> > +	mutex_lock(&trace_link_mutex);
> 
> that seems too much, we could add link->mutex

This penalizes all links though. Scanning through some other link types
in the kernel, most that I see that support update_prog have opted for a
global mutex as opposed to a per-link mutex. To me, it seems better to
go with this since contention is low instead of making link structs
bigger?
 
> > +
> > +	if (old_prog && link->prog != old_prog) {
> > +		err = -EPERM;
> > +		goto out;
> > +	}
> > +	old_prog = link->prog;
> > +	if (old_prog->type != new_prog->type ||
> > +	    old_prog->expected_attach_type != new_prog->expected_attach_type) {
> > +		err = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	mutex_lock(&new_prog->aux->dst_mutex);
> > +
> > +	if (!new_prog->aux->dst_trampoline ||
> > +	    new_prog->aux->dst_trampoline->key != tr_link->trampoline->key) {
> 
> hum, would be easier (and still usefull) to allow just programs for the same function?

This behavior mirrors that of bpf_tracing_prog_attach below. I think
you'd lose some utility if you required dst_trampoline to match
trampoline here. A practical use case I can think of would be that you
might want to reuse the same program for several links or
detach/reattach the same program. In these scenarios, dst_trampoline
would have been cleared previously, so you'd need to do the
compatibility check again.
 
> > +		bpf_trampoline_unpack_key(tr_link->trampoline->key, NULL,
> > +					  &btf_id);
> > +		/* If there is no saved target, or the target associated with
> > +		 * this link is different from the destination specified at
> > +		 * load time, we need to check for compatibility.
> > +		 */
> > +		err = bpf_check_attach_target(NULL, new_prog, tr_link->tgt_prog,
> > +					      btf_id, &tgt_info);
> > +		if (err)
> > +			goto out_unlock;
> > +	}
> > +
> > +	err = bpf_trampoline_update_prog(&tr_link->link, new_prog,
> > +					 tr_link->trampoline);
> > +	if (err)
> > +		goto out_unlock;
> > +
> > +	/* Clear the trampoline, mod, and target prog from new_prog->aux to make
> > +	 * sure the original attach destination is not kept alive after a
> > +	 * program is (re-)attached to another target.
> > +	 */
> > +	if (new_prog->aux->dst_prog)
> > +		bpf_prog_put(new_prog->aux->dst_prog);
> > +	bpf_trampoline_put(new_prog->aux->dst_trampoline);
> 
> would it be possible just to take tr->mutex and unlink/link
> the programs, something like:
> 
>         mutex_lock(&tr->mutex);
> 
> 	__bpf_trampoline_unlink_prog(old_prog)
> 	__bpf_trampoline_link_prog(new_prog)
> 
>         mutex_unlock(&tr->mutex);

This is non-atomic though, so there would be some period between unlink
and link where the link target's trampoline doesn't have the program:

[old_prog]
[] <-
[new_prog]

Maybe it's not such a big deal for pure tracing stuff like fentry/fexit,
but it could create some weird and unexpected effects with freplace
links. Unfortunately, to guarantee atomicity, I think you have to push
the intent to actually update a specific program in a trampoline down a
layer (i.e. bpf_trampoline_update_prog).
  
> I might be missing something but this way we wouldn't need
> the arch chages in the following patches?

Alexei said he doesn't want to support update_prog for fentry/fexit;
dropping that from this series (patches 3-6) would remove arch-specific
stuff.

> jirka
> 
> 
> > +	module_put(new_prog->aux->mod);
> > +
> > +	new_prog->aux->dst_prog = NULL;
> > +	new_prog->aux->dst_trampoline = NULL;
> > +	new_prog->aux->mod = tgt_info.tgt_mod;
> > +	tgt_info.tgt_mod = NULL; /* Make module_put() below do nothing. */
> > +out_unlock:
> > +	mutex_unlock(&new_prog->aux->dst_mutex);
> > +out:
> > +	mutex_unlock(&trace_link_mutex);
> > +	module_put(tgt_info.tgt_mod);
> > +	return err;
> > +}
> > +
> >  static const struct bpf_link_ops bpf_tracing_link_lops = {
> >  	.release = bpf_tracing_link_release,
> >  	.dealloc = bpf_tracing_link_dealloc,
> >  	.show_fdinfo = bpf_tracing_link_show_fdinfo,
> >  	.fill_link_info = bpf_tracing_link_fill_link_info,
> > +	.update_prog = bpf_tracing_link_update_prog,
> >  };
> >  
> 
> SNIP

Thanks for taking a look!

Jordan

[RFC PATCH bpf-next 2/7] bpf: Enable BPF_LINK_UPDATE for freplace links

[Jordan Rife]

Implement program update logic for freplace links.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 kernel/bpf/trampoline.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 010bcba0db65..0b6a5433dd42 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -614,6 +614,21 @@ static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
 					struct bpf_prog *new_prog,
 					struct bpf_trampoline *tr)
 {
+	enum bpf_tramp_prog_type kind;
+	int err = 0;
+
+	kind = bpf_attach_type_to_tramp(link->link.prog);
+	if (kind == BPF_TRAMP_REPLACE) {
+		WARN_ON_ONCE(!tr->extension_prog);
+		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
+					 tr->extension_prog->bpf_func,
+					 new_prog->bpf_func);
+		if (err)
+			return err;
+		tr->extension_prog = new_prog;
+		return 0;
+	}
+
 	return -ENOTSUPP;
 }
 
-- 
2.43.0

[RFC PATCH bpf-next 3/7] bpf: Enable BPF_LINK_UPDATE for fentry/fexit/fmod_ret links

[Jordan Rife]

Implement program update for other link types supported by
bpf_tracing_link_lops (fentry, fexit, fmod_ret, ...). I wanted to make
the implementation generic so that no architecture-specific support
would be required, but couldn't think of a good way to do this:

* I considered updating link.prog before calling bpf_trampoline_update
  and reverting it back to the old prog if the update fails, but this
  could create inconsistencies with concurrent operations that read
  links where they see the uncommitted program associated with the link.
* I considered making a deep copy of the link whose program is being
  updated and putting a pointer to that copy into tlinks when calling
  bpf_trampoline_get_progs where the copy references the new program
  instead of the current program. This would avoid updating the original
  link.prog before the update was committed; however, this seemed
  slightly hacky and I wasn't sure if this was better than just making
  the architecture-specific layer aware of the intent to update one of
  the link programs.

This patch sets up the scaffolding for trampoline program updates while
subsequent patches enable this for various architectures. For now, only
x86, arm64, and s390 are implemented since that's what I could test in
CI.

Add update_link and update_prog to bpf_tramp_links. When these are
set, arch_bpf_trampoline_size() and arch_prepare_bpf_trampoline() use
update_prog in place of update_link->link.prog when calculating the
trampoline size and constructing a new trampoline image. link.prog is
only updated after the trampoline update is successfully committed. If
the current architecture does not support program updates (i.e.
bpf_trampoline_supports_update_prog() is not implemented) then the
BPF_LINK_UPDATE operation will return -ENOTSUPP.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 include/linux/bpf.h     | 10 ++++++++++
 kernel/bpf/trampoline.c | 33 +++++++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 23fcbcd26aa4..7daf40cbdd9b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1215,6 +1215,8 @@ enum {
 
 struct bpf_tramp_links {
 	struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS];
+	struct bpf_tramp_link *update_link;
+	struct bpf_prog *update_prog;
 	int nr_links;
 };
 
@@ -1245,6 +1247,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
 				const struct btf_func_model *m, u32 flags,
 				struct bpf_tramp_links *tlinks,
 				void *func_addr);
+bool bpf_trampoline_supports_update_prog(void);
 void *arch_alloc_bpf_trampoline(unsigned int size);
 void arch_free_bpf_trampoline(void *image, unsigned int size);
 int __must_check arch_protect_bpf_trampoline(void *image, unsigned int size);
@@ -1840,6 +1843,13 @@ struct bpf_tramp_link {
 	u64 cookie;
 };
 
+static inline struct bpf_prog *
+bpf_tramp_links_prog(struct bpf_tramp_links *tl, int i)
+{
+	return tl->links[i] == tl->update_link ? tl->update_prog :
+						 tl->links[i]->link.prog;
+}
+
 struct bpf_shim_tramp_link {
 	struct bpf_tramp_link link;
 	struct bpf_trampoline *trampoline;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 0b6a5433dd42..0c0373b76816 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -230,7 +230,10 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 }
 
 static struct bpf_tramp_links *
-bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
+bpf_trampoline_get_progs(const struct bpf_trampoline *tr,
+			 struct bpf_tramp_link *update_link,
+			 struct bpf_prog *update_prog,
+			 int *total, bool *ip_arg)
 {
 	struct bpf_tramp_link *link;
 	struct bpf_tramp_links *tlinks;
@@ -250,6 +253,11 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_a
 		hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
 			*ip_arg |= link->link.prog->call_get_func_ip;
 			*links++ = link;
+			if (link == update_link) {
+				*ip_arg |= update_prog->call_get_func_ip;
+				tlinks[kind].update_link = update_link;
+				tlinks[kind].update_prog = update_prog;
+			}
 		}
 	}
 	return tlinks;
@@ -395,7 +403,10 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, int size)
 	return ERR_PTR(err);
 }
 
-static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
+static int __bpf_trampoline_update(struct bpf_trampoline *tr,
+				   struct bpf_tramp_link *update_link,
+				   struct bpf_prog *update_prog,
+				   bool lock_direct_mutex)
 {
 	struct bpf_tramp_image *im;
 	struct bpf_tramp_links *tlinks;
@@ -403,7 +414,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 	bool ip_arg = false;
 	int err, total, size;
 
-	tlinks = bpf_trampoline_get_progs(tr, &total, &ip_arg);
+	if (update_link && !bpf_trampoline_supports_update_prog())
+		return -ENOTSUPP;
+
+	tlinks = bpf_trampoline_get_progs(tr, update_link, update_prog,
+					  &total, &ip_arg);
 	if (IS_ERR(tlinks))
 		return PTR_ERR(tlinks);
 
@@ -506,6 +521,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 	goto out;
 }
 
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
+{
+	return __bpf_trampoline_update(tr, NULL, NULL, lock_direct_mutex);
+}
+
 static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
 {
 	switch (prog->expected_attach_type) {
@@ -629,7 +649,7 @@ static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
 		return 0;
 	}
 
-	return -ENOTSUPP;
+	return __bpf_trampoline_update(tr, link, new_prog, true);
 }
 
 int bpf_trampoline_update_prog(struct bpf_tramp_link *link,
@@ -1139,6 +1159,11 @@ arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image
 	return -ENOTSUPP;
 }
 
+bool __weak bpf_trampoline_supports_update_prog(void)
+{
+	return false;
+}
+
 void * __weak arch_alloc_bpf_trampoline(unsigned int size)
 {
 	void *image;
-- 
2.43.0

Re: [RFC PATCH bpf-next 3/7] bpf: Enable BPF_LINK_UPDATE for fentry/fexit/fmod_ret links

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 4901 bytes --]

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 23fcbcd26..7daf40cbd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1215,6 +1215,8 @@ enum {
>
>  struct bpf_tramp_links {
>  	struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS];
> +	struct bpf_tramp_link *update_link;
> +	struct bpf_prog *update_prog;
>  	int nr_links;
>  };

[ ... ]

> @@ -1840,6 +1843,13 @@ struct bpf_tramp_link {
>  	u64 cookie;
>  };
>
> +static inline struct bpf_prog *
> +bpf_tramp_links_prog(struct bpf_tramp_links *tl, int i)
> +{
> +	return tl->links[i] == tl->update_link ? tl->update_prog :
> +						 tl->links[i]->link.prog;
> +}

This helper is added but the architecture-specific code in
arch/x86/net/bpf_jit_comp.c, arch/arm64/net/bpf_jit_comp.c, and
arch/s390/net/bpf_jit_comp.c continues to access tl->links[i]->link.prog
directly. When __bpf_trampoline_update() passes tlinks with update_link
and update_prog set, won't arch_prepare_bpf_trampoline() and
arch_bpf_trampoline_size() use the old program instead of the new one?

For example, in arch/x86/net/bpf_jit_comp.c around line 2966:
    struct bpf_prog *p = l->link.prog;

This should probably use bpf_tramp_links_prog() to get the correct
program during updates. The same pattern appears in the other arch
implementations.

> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 171440f37..486f945f6 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -232,7 +232,10 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
>  }
>
>  static struct bpf_tramp_links *
> -bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
> +bpf_trampoline_get_progs(const struct bpf_trampoline *tr,
> +			 struct bpf_tramp_link *update_link,
> +			 struct bpf_prog *update_prog,
> +			 int *total, bool *ip_arg)
>  {
>  	struct bpf_tramp_link *link;
>  	struct bpf_tramp_links *tlinks;
> @@ -252,6 +255,11 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_a
>  		hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
>  			*ip_arg |= link->link.prog->call_get_func_ip;
>  			*links++ = link;
> +			if (link == update_link) {
> +				*ip_arg |= update_prog->call_get_func_ip;
> +				tlinks[kind].update_link = update_link;
> +				tlinks[kind].update_prog = update_prog;
> +			}
>  		}
>  	}
>  	return tlinks;

[ ... ]

> @@ -397,7 +405,10 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, int size)
>  	return ERR_PTR(err);
>  }
>
> -static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
> +static int __bpf_trampoline_update(struct bpf_trampoline *tr,
> +				   struct bpf_tramp_link *update_link,
> +				   struct bpf_prog *update_prog,
> +				   bool lock_direct_mutex)
>  {
>  	struct bpf_tramp_image *im;
>  	struct bpf_tramp_links *tlinks;
> @@ -405,7 +416,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
>  	bool ip_arg = false;
>  	int err, total, size;
>
> -	tlinks = bpf_trampoline_get_progs(tr, &total, &ip_arg);
> +	if (update_link && !bpf_trampoline_supports_update_prog())
> +		return -ENOTSUPP;
> +
> +	tlinks = bpf_trampoline_get_progs(tr, update_link, update_prog,
> +					  &total, &ip_arg);

[ ... ]

> @@ -503,6 +518,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
>  	goto out;
>  }
>
> +static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
> +{
> +	return __bpf_trampoline_update(tr, NULL, NULL, lock_direct_mutex);
> +}
> +
>  static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
>  {
>  	switch (prog->expected_attach_type) {
> @@ -626,7 +646,7 @@ static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
>  		return 0;
>  	}
>
> -	return -ENOTSUPP;
> +	return __bpf_trampoline_update(tr, link, new_prog, true);
>  }

[ ... ]

> @@ -1136,6 +1156,11 @@ arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image
>  	return -ENOTSUPP;
>  }
>
> +bool __weak bpf_trampoline_supports_update_prog(void)
> +{
> +	return false;
> +}

The commit message says "For now, only x86, arm64, and s390 are
implemented" but none of these architectures appear to be updated in
this patch or in the visible preceding commits (627b0f207, b0184022d).
Without overriding bpf_trampoline_supports_update_prog() to return true
and updating the arch code to use bpf_tramp_links_prog(), the feature
will always return -ENOTSUPP on all architectures. Was this patch meant
to include the arch-specific implementations, or are they in a separate
series?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19450205468

Re: [RFC PATCH bpf-next 3/7] bpf: Enable BPF_LINK_UPDATE for fentry/fexit/fmod_ret links

[Jordan Rife]

On Tue, Nov 18, 2025 at 01:19:33AM +0000, bot+bpf-ci@kernel.org wrote:
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 23fcbcd26..7daf40cbd 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1215,6 +1215,8 @@ enum {
> >
> >  struct bpf_tramp_links {
> >  	struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS];
> > +	struct bpf_tramp_link *update_link;
> > +	struct bpf_prog *update_prog;
> >  	int nr_links;
> >  };
> 
> [ ... ]
> 
> > @@ -1840,6 +1843,13 @@ struct bpf_tramp_link {
> >  	u64 cookie;
> >  };
> >
> > +static inline struct bpf_prog *
> > +bpf_tramp_links_prog(struct bpf_tramp_links *tl, int i)
> > +{
> > +	return tl->links[i] == tl->update_link ? tl->update_prog :
> > +						 tl->links[i]->link.prog;
> > +}
> 
> This helper is added but the architecture-specific code in
> arch/x86/net/bpf_jit_comp.c, arch/arm64/net/bpf_jit_comp.c, and
> arch/s390/net/bpf_jit_comp.c continues to access tl->links[i]->link.prog
> directly. When __bpf_trampoline_update() passes tlinks with update_link
> and update_prog set, won't arch_prepare_bpf_trampoline() and
> arch_bpf_trampoline_size() use the old program instead of the new one?
> 
> For example, in arch/x86/net/bpf_jit_comp.c around line 2966:
>     struct bpf_prog *p = l->link.prog;
> 
> This should probably use bpf_tramp_links_prog() to get the correct
> program during updates. The same pattern appears in the other arch
> implementations.

This is done in follow up patches in this series.

> > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> > index 171440f37..486f945f6 100644
> > --- a/kernel/bpf/trampoline.c
> > +++ b/kernel/bpf/trampoline.c
> > @@ -232,7 +232,10 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
> >  }
> >
> >  static struct bpf_tramp_links *
> > -bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
> > +bpf_trampoline_get_progs(const struct bpf_trampoline *tr,
> > +			 struct bpf_tramp_link *update_link,
> > +			 struct bpf_prog *update_prog,
> > +			 int *total, bool *ip_arg)
> >  {
> >  	struct bpf_tramp_link *link;
> >  	struct bpf_tramp_links *tlinks;
> > @@ -252,6 +255,11 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_a
> >  		hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
> >  			*ip_arg |= link->link.prog->call_get_func_ip;
> >  			*links++ = link;
> > +			if (link == update_link) {
> > +				*ip_arg |= update_prog->call_get_func_ip;
> > +				tlinks[kind].update_link = update_link;
> > +				tlinks[kind].update_prog = update_prog;
> > +			}
> >  		}
> >  	}
> >  	return tlinks;
> 
> [ ... ]
> 
> > @@ -397,7 +405,10 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, int size)
> >  	return ERR_PTR(err);
> >  }
> >
> > -static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
> > +static int __bpf_trampoline_update(struct bpf_trampoline *tr,
> > +				   struct bpf_tramp_link *update_link,
> > +				   struct bpf_prog *update_prog,
> > +				   bool lock_direct_mutex)
> >  {
> >  	struct bpf_tramp_image *im;
> >  	struct bpf_tramp_links *tlinks;
> > @@ -405,7 +416,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
> >  	bool ip_arg = false;
> >  	int err, total, size;
> >
> > -	tlinks = bpf_trampoline_get_progs(tr, &total, &ip_arg);
> > +	if (update_link && !bpf_trampoline_supports_update_prog())
> > +		return -ENOTSUPP;
> > +
> > +	tlinks = bpf_trampoline_get_progs(tr, update_link, update_prog,
> > +					  &total, &ip_arg);
> 
> [ ... ]
> 
> > @@ -503,6 +518,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
> >  	goto out;
> >  }
> >
> > +static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
> > +{
> > +	return __bpf_trampoline_update(tr, NULL, NULL, lock_direct_mutex);
> > +}
> > +
> >  static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
> >  {
> >  	switch (prog->expected_attach_type) {
> > @@ -626,7 +646,7 @@ static int __bpf_trampoline_update_prog(struct bpf_tramp_link *link,
> >  		return 0;
> >  	}
> >
> > -	return -ENOTSUPP;
> > +	return __bpf_trampoline_update(tr, link, new_prog, true);
> >  }
> 
> [ ... ]
> 
> > @@ -1136,6 +1156,11 @@ arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image
> >  	return -ENOTSUPP;
> >  }
> >
> > +bool __weak bpf_trampoline_supports_update_prog(void)
> > +{
> > +	return false;
> > +}
> 
> The commit message says "For now, only x86, arm64, and s390 are
> implemented" but none of these architectures appear to be updated in
> this patch or in the visible preceding commits (627b0f207, b0184022d).
> Without overriding bpf_trampoline_supports_update_prog() to return true
> and updating the arch code to use bpf_tramp_links_prog(), the feature
> will always return -ENOTSUPP on all architectures. Was this patch meant
> to include the arch-specific implementations, or are they in a separate
> series?

The architecture-specific implementations for x86, arm64, and s390 are
in follow up patches in this series.

> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19450205468

[RFC PATCH bpf-next 4/7] bpf, x86: Make program update work for trampoline ops

[Jordan Rife]

Use update_prog in place of current link prog when link matches
update_link.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 arch/x86/net/bpf_jit_comp.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 36a0d4db9f68..2b3ea20b39b9 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2956,15 +2956,13 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog,
 }
 
 static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
-			   struct bpf_tramp_link *l, int stack_size,
+			   struct bpf_prog *p, u64 cookie, int stack_size,
 			   int run_ctx_off, bool save_ret,
 			   void *image, void *rw_image)
 {
 	u8 *prog = *pprog;
 	u8 *jmp_insn;
 	int ctx_cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
-	struct bpf_prog *p = l->link.prog;
-	u64 cookie = l->cookie;
 
 	/* mov rdi, cookie */
 	emit_mov_imm64(&prog, BPF_REG_1, (long) cookie >> 32, (u32) (long) cookie);
@@ -3079,7 +3077,8 @@ static int invoke_bpf(const struct btf_func_model *m, u8 **pprog,
 	u8 *prog = *pprog;
 
 	for (i = 0; i < tl->nr_links; i++) {
-		if (invoke_bpf_prog(m, &prog, tl->links[i], stack_size,
+		if (invoke_bpf_prog(m, &prog, bpf_tramp_links_prog(tl, i),
+				    tl->links[i]->cookie, stack_size,
 				    run_ctx_off, save_ret, image, rw_image))
 			return -EINVAL;
 	}
@@ -3101,8 +3100,9 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
 	emit_mov_imm32(&prog, false, BPF_REG_0, 0);
 	emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
 	for (i = 0; i < tl->nr_links; i++) {
-		if (invoke_bpf_prog(m, &prog, tl->links[i], stack_size, run_ctx_off, true,
-				    image, rw_image))
+		if (invoke_bpf_prog(m, &prog, bpf_tramp_links_prog(tl, i),
+				    tl->links[i]->cookie, stack_size,
+				    run_ctx_off, true, image, rw_image))
 			return -EINVAL;
 
 		/* mod_ret prog stored return value into [rbp - 8]. Emit:
@@ -3486,6 +3486,11 @@ int arch_protect_bpf_trampoline(void *image, unsigned int size)
 	return 0;
 }
 
+bool bpf_trampoline_supports_update_prog(void)
+{
+	return true;
+}
+
 int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
 				const struct btf_func_model *m, u32 flags,
 				struct bpf_tramp_links *tlinks,
-- 
2.43.0

[RFC PATCH bpf-next 5/7] bpf, s390: Make program update work for trampoline ops

[Jordan Rife]

Use update_prog in place of current link prog when link matches
update_link.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 arch/s390/net/bpf_jit_comp.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index cf461d76e9da..bf70302d1009 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -2508,20 +2508,19 @@ static void load_imm64(struct bpf_jit *jit, int dst_reg, u64 val)
 
 static int invoke_bpf_prog(struct bpf_tramp_jit *tjit,
 			   const struct btf_func_model *m,
-			   struct bpf_tramp_link *tlink, bool save_ret)
+			   struct bpf_prog *p, u64 cookie, bool save_ret)
 {
 	struct bpf_jit *jit = &tjit->common;
 	int cookie_off = tjit->run_ctx_off +
 			 offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
-	struct bpf_prog *p = tlink->link.prog;
 	int patch;
 
 	/*
-	 * run_ctx.cookie = tlink->cookie;
+	 * run_ctx.cookie = cookie;
 	 */
 
-	/* %r0 = tlink->cookie */
-	load_imm64(jit, REG_W0, tlink->cookie);
+	/* %r0 = cookie */
+	load_imm64(jit, REG_W0, cookie);
 	/* stg %r0,cookie_off(%r15) */
 	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W0, REG_0, REG_15, cookie_off);
 
@@ -2768,7 +2767,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	}
 
 	for (i = 0; i < fentry->nr_links; i++)
-		if (invoke_bpf_prog(tjit, m, fentry->links[i],
+		if (invoke_bpf_prog(tjit, m, bpf_tramp_links_prog(fentry, i),
+				    fentry->links[i]->cookie,
 				    flags & BPF_TRAMP_F_RET_FENTRY_RET))
 			return -EINVAL;
 
@@ -2782,7 +2782,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 		       0xf000 | tjit->retval_off);
 
 		for (i = 0; i < fmod_ret->nr_links; i++) {
-			if (invoke_bpf_prog(tjit, m, fmod_ret->links[i], true))
+			if (invoke_bpf_prog(tjit, m,
+					    bpf_tramp_links_prog(fmod_ret, i),
+					    fmod_ret->links[i]->cookie, true))
 				return -EINVAL;
 
 			/*
@@ -2850,7 +2852,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	/* do_fexit: */
 	tjit->do_fexit = jit->prg;
 	for (i = 0; i < fexit->nr_links; i++)
-		if (invoke_bpf_prog(tjit, m, fexit->links[i], false))
+		if (invoke_bpf_prog(tjit, m, bpf_tramp_links_prog(fexit, i),
+				    fexit->links[i]->cookie, false))
 			return -EINVAL;
 
 	if (flags & BPF_TRAMP_F_CALL_ORIG) {
@@ -2946,6 +2949,11 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
 	return ret < 0 ? ret : tjit.common.prg;
 }
 
+bool bpf_trampoline_supports_update_prog(void)
+{
+	return true;
+}
+
 bool bpf_jit_supports_subprog_tailcalls(void)
 {
 	return true;
-- 
2.43.0

[RFC PATCH bpf-next 6/7] bpf, arm64: Make program update work for trampoline ops

[Jordan Rife]

Use update_prog in place of current link prog when link matches
update_link.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 arch/arm64/net/bpf_jit_comp.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 0c9a50a1e73e..1725d4cebdf2 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -2284,24 +2284,23 @@ bool bpf_jit_supports_subprog_tailcalls(void)
 	return true;
 }
 
-static void invoke_bpf_prog(struct jit_ctx *ctx, struct bpf_tramp_link *l,
+static void invoke_bpf_prog(struct jit_ctx *ctx, struct bpf_prog *p, u64 cookie,
 			    int bargs_off, int retval_off, int run_ctx_off,
 			    bool save_ret)
 {
 	__le32 *branch;
 	u64 enter_prog;
 	u64 exit_prog;
-	struct bpf_prog *p = l->link.prog;
 	int cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
 
 	enter_prog = (u64)bpf_trampoline_enter(p);
 	exit_prog = (u64)bpf_trampoline_exit(p);
 
-	if (l->cookie == 0) {
+	if (cookie == 0) {
 		/* if cookie is zero, one instruction is enough to store it */
 		emit(A64_STR64I(A64_ZR, A64_SP, run_ctx_off + cookie_off), ctx);
 	} else {
-		emit_a64_mov_i64(A64_R(10), l->cookie, ctx);
+		emit_a64_mov_i64(A64_R(10), cookie, ctx);
 		emit(A64_STR64I(A64_R(10), A64_SP, run_ctx_off + cookie_off),
 		     ctx);
 	}
@@ -2362,7 +2361,8 @@ static void invoke_bpf_mod_ret(struct jit_ctx *ctx, struct bpf_tramp_links *tl,
 	 */
 	emit(A64_STR64I(A64_ZR, A64_SP, retval_off), ctx);
 	for (i = 0; i < tl->nr_links; i++) {
-		invoke_bpf_prog(ctx, tl->links[i], bargs_off, retval_off,
+		invoke_bpf_prog(ctx, bpf_tramp_links_prog(tl, i),
+				tl->links[i]->cookie, bargs_off, retval_off,
 				run_ctx_off, true);
 		/* if (*(u64 *)(sp + retval_off) !=  0)
 		 *	goto do_fexit;
@@ -2656,8 +2656,9 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
 	}
 
 	for (i = 0; i < fentry->nr_links; i++)
-		invoke_bpf_prog(ctx, fentry->links[i], bargs_off,
-				retval_off, run_ctx_off,
+		invoke_bpf_prog(ctx, bpf_tramp_links_prog(fentry, i),
+				fentry->links[i]->cookie, bargs_off, retval_off,
+				run_ctx_off,
 				flags & BPF_TRAMP_F_RET_FENTRY_RET);
 
 	if (fmod_ret->nr_links) {
@@ -2691,7 +2692,8 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
 	}
 
 	for (i = 0; i < fexit->nr_links; i++)
-		invoke_bpf_prog(ctx, fexit->links[i], bargs_off, retval_off,
+		invoke_bpf_prog(ctx, bpf_tramp_links_prog(fexit, i),
+				fexit->links[i]->cookie, bargs_off, retval_off,
 				run_ctx_off, false);
 
 	if (flags & BPF_TRAMP_F_CALL_ORIG) {
@@ -2829,6 +2831,11 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *ro_image,
 	return ret;
 }
 
+bool bpf_trampoline_supports_update_prog(void)
+{
+	return true;
+}
+
 static bool is_long_jump(void *ip, void *target)
 {
 	long offset;
-- 
2.43.0

[RFC PATCH bpf-next 7/7] selftests/bpf: Test BPF_LINK_UPDATE behavior for tracing links

[Jordan Rife]

Exercise a series of edge cases and happy path scenarios across a gamut
of link types (fentry, fmod_ret, fexit, freplace) to test
BPF_LINK_UPDATE behavior for tracing links. This test swaps
fentry/fmod_ret/fexit programs in-place and makes sure that the sequence
and attach cookie are as expected based on the link positions.

Signed-off-by: Jordan Rife <jordan@jrife.io>
---
 .../bpf/prog_tests/prog_update_tracing.c      | 460 ++++++++++++++++++
 .../selftests/bpf/progs/prog_update_tracing.c | 133 +++++
 2 files changed, 593 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/prog_update_tracing.c
 create mode 100644 tools/testing/selftests/bpf/progs/prog_update_tracing.c

diff --git a/tools/testing/selftests/bpf/prog_tests/prog_update_tracing.c b/tools/testing/selftests/bpf/prog_tests/prog_update_tracing.c
new file mode 100644
index 000000000000..0b1e0d780c82
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/prog_update_tracing.c
@@ -0,0 +1,460 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <network_helpers.h>
+#include <test_progs.h>
+#include "prog_update_tracing.skel.h"
+#include "test_pkt_access.skel.h"
+
+static bool assert_program_order(struct prog_update_tracing *skel_trace,
+				 struct test_pkt_access *skel_pkt,
+				 const struct prog_update_tracing__bss *expected)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts_trace);
+	LIBBPF_OPTS(bpf_test_run_opts, topts_skb,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+	int prog_fd;
+
+	prog_fd = bpf_program__fd(skel_trace->progs.fmod_ret1);
+	if (!ASSERT_OK(bpf_prog_test_run_opts(prog_fd, &topts_trace),
+		       "bpf_prog_test_run trace"))
+		return false;
+
+	if (!ASSERT_EQ(skel_trace->bss->fentry1_seq,
+		       expected->fentry1_seq, "fentry1_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry1_cookie,
+		       expected->fentry1_cookie, "fentry1_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry2_seq,
+		       expected->fentry2_seq, "fentry2_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry2_cookie,
+		       expected->fentry2_cookie, "fentry2_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fmod_ret1_seq,
+		       expected->fmod_ret1_seq, "fmod_ret1_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fmod_ret1_cookie,
+		       expected->fmod_ret1_cookie, "fmod_ret1_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fmod_ret2_seq,
+		       expected->fmod_ret2_seq, "fmod_ret2_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fmod_ret2_cookie,
+		       expected->fmod_ret2_cookie, "fmod_ret2_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit1_seq,
+		       expected->fexit1_seq, "fexit1_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit1_cookie,
+		       expected->fexit1_cookie, "fexit1_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit2_seq,
+		       expected->fexit2_seq, "fexit2_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit2_cookie,
+		       expected->fexit2_cookie, "fexit2_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->sequence, expected->sequence,
+		       "sequence"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->sequence_bpf, 0, "sequence_bpf"))
+		return false;
+
+	prog_fd = bpf_program__fd(skel_pkt->progs.test_pkt_access);
+	if (!ASSERT_OK(bpf_prog_test_run_opts(prog_fd, &topts_skb),
+		       "bpf_prog_test_run skb"))
+		return false;
+
+	if (!ASSERT_EQ(skel_trace->bss->sequence, expected->sequence,
+		       "sequence"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry1_bpf_seq,
+		       expected->fentry1_bpf_seq, "fentry1_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry1_bpf_cookie,
+		       expected->fentry1_bpf_cookie, "fentry1_bpf_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry2_bpf_seq,
+		       expected->fentry2_bpf_seq, "fentry2_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fentry2_bpf_cookie,
+		       expected->fentry2_bpf_cookie, "fentry2_bpf_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->freplace1_bpf_seq,
+		       expected->freplace1_bpf_seq, "freplace1_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->freplace2_bpf_seq,
+		       expected->freplace2_bpf_seq, "freplace2_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit1_bpf_seq,
+		       expected->fexit1_bpf_seq, "fexit1_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit1_bpf_cookie,
+		       expected->fexit1_bpf_cookie, "fexit1_bpf_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit2_bpf_seq,
+		       expected->fexit2_bpf_seq, "fexit2_bpf_seq"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->fexit2_bpf_cookie,
+		       expected->fexit2_bpf_cookie, "fexit2_bpf_cookie"))
+		return false;
+	if (!ASSERT_EQ(skel_trace->bss->sequence_bpf, expected->sequence_bpf,
+		       "sequence_bpf"))
+		return false;
+
+	memset(skel_trace->bss, 0, sizeof(*skel_trace->bss));
+
+	return true;
+}
+
+void test_prog_update_tracing(void)
+{
+	const struct prog_update_tracing__bss expected_inverted = {
+		.fentry1_seq = 2,
+		.fentry1_cookie = 102,
+		.fentry2_seq = 1,
+		.fentry2_cookie = 101,
+		.fmod_ret1_seq = 4,
+		.fmod_ret1_cookie = 104,
+		.fmod_ret2_seq = 3,
+		.fmod_ret2_cookie = 103,
+		.fexit1_seq = 6,
+		.fexit1_cookie = 106,
+		.fexit2_seq = 5,
+		.fexit2_cookie = 105,
+		.sequence = 6,
+		.fentry1_bpf_seq = 2,
+		.fentry1_bpf_cookie = 202,
+		.fentry2_bpf_seq = 1,
+		.fentry2_bpf_cookie = 201,
+		.freplace1_bpf_seq = 3,
+		.freplace2_bpf_seq = 0,
+		.fexit1_bpf_seq = 5,
+		.fexit1_bpf_cookie = 205,
+		.fexit2_bpf_seq = 4,
+		.fexit2_bpf_cookie = 204,
+		.sequence_bpf = 5,
+	};
+	const struct prog_update_tracing__bss expected_normal = {
+		.fentry1_seq = 1,
+		.fentry1_cookie = 101,
+		.fentry2_seq = 2,
+		.fentry2_cookie = 102,
+		.fmod_ret1_seq = 3,
+		.fmod_ret1_cookie = 103,
+		.fmod_ret2_seq = 4,
+		.fmod_ret2_cookie = 104,
+		.fexit1_seq = 5,
+		.fexit1_cookie = 105,
+		.fexit2_seq = 6,
+		.fexit2_cookie = 106,
+		.sequence = 6,
+		.fentry1_bpf_seq = 1,
+		.fentry1_bpf_cookie = 201,
+		.fentry2_bpf_seq = 2,
+		.fentry2_bpf_cookie = 202,
+		.freplace1_bpf_seq = 3,
+		.freplace2_bpf_seq = 0,
+		.fexit1_bpf_seq = 4,
+		.fexit1_bpf_cookie = 204,
+		.fexit2_bpf_seq = 5,
+		.fexit2_bpf_cookie = 205,
+		.sequence_bpf = 5,
+	};
+	LIBBPF_OPTS(bpf_link_update_opts, update_opts);
+	LIBBPF_OPTS(bpf_trace_opts, trace_opts);
+	struct prog_update_tracing *skel_trace1 = NULL;
+	struct prog_update_tracing *skel_trace2 = NULL;
+	struct test_pkt_access *skel_pkt1 = NULL;
+	struct test_pkt_access *skel_pkt2 = NULL;
+	int link_fd, prog_fd, err;
+	struct bpf_link *link;
+
+	skel_trace1 = prog_update_tracing__open();
+	if (!ASSERT_OK_PTR(skel_trace1, "skel_trace1"))
+		goto cleanup;
+	skel_pkt1 = test_pkt_access__open_and_load();
+	if (!ASSERT_OK_PTR(skel_pkt1, "skel_pkt1"))
+		goto cleanup;
+	prog_fd = bpf_program__fd(skel_pkt1->progs.test_pkt_access);
+	bpf_program__set_attach_target(skel_trace1->progs.fentry1_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace1->progs.fentry2_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace1->progs.fexit1_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace1->progs.fexit2_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace1->progs.freplace1_bpf,
+				       prog_fd, "test_pkt_access_subprog3");
+	bpf_program__set_attach_target(skel_trace1->progs.freplace2_bpf,
+				       prog_fd, "test_pkt_access_subprog3");
+	bpf_program__set_attach_target(skel_trace1->progs.freplace3_bpf,
+				       prog_fd, "get_skb_ifindex");
+	err = prog_update_tracing__load(skel_trace1);
+	if (!ASSERT_OK(err, "skel_trace1 load"))
+		goto cleanup;
+	trace_opts.cookie = expected_normal.fentry2_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fentry2,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fentry2"))
+		goto cleanup;
+	skel_trace1->links.fentry2 = link;
+	trace_opts.cookie = expected_normal.fentry1_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fentry1,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fentry1"))
+		goto cleanup;
+	skel_trace1->links.fentry1 = link;
+	trace_opts.cookie = expected_normal.fmod_ret2_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fmod_ret2,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fmod_ret2"))
+		goto cleanup;
+	skel_trace1->links.fmod_ret2 = link;
+	trace_opts.cookie = expected_normal.fmod_ret1_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fmod_ret1,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fmod_ret1"))
+		goto cleanup;
+	skel_trace1->links.fmod_ret1 = link;
+	trace_opts.cookie = expected_normal.fexit2_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fexit2,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fexit2"))
+		goto cleanup;
+	skel_trace1->links.fexit2 = link;
+	trace_opts.cookie = expected_normal.fexit1_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fexit1,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fexit1"))
+		goto cleanup;
+	skel_trace1->links.fexit1 = link;
+	trace_opts.cookie = expected_normal.fentry2_bpf_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fentry2_bpf,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fentry2_bpf"))
+		goto cleanup;
+	skel_trace1->links.fentry2_bpf = link;
+	trace_opts.cookie = expected_normal.fentry1_bpf_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fentry1_bpf,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fentry1_bpf"))
+		goto cleanup;
+	skel_trace1->links.fentry1_bpf = link;
+	trace_opts.cookie = expected_normal.fexit2_bpf_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fexit2_bpf,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fexit2_bpf"))
+		goto cleanup;
+	skel_trace1->links.fexit2_bpf = link;
+	trace_opts.cookie = expected_normal.fexit1_bpf_cookie;
+	link = bpf_program__attach_trace_opts(skel_trace1->progs.fexit1_bpf,
+					      &trace_opts);
+	if (!ASSERT_OK_PTR(link, "attach fexit1_bpf"))
+		goto cleanup;
+	skel_trace1->links.fexit1_bpf = link;
+	link = bpf_program__attach_trace(skel_trace1->progs.freplace1_bpf);
+	if (!ASSERT_OK_PTR(link, "attach freplace1_bpf"))
+		goto cleanup;
+	skel_trace1->links.freplace1_bpf = link;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Program update should fail if expected_attach_type is a mismatch. */
+	err = bpf_link__update_program(skel_trace1->links.fentry1,
+				       skel_trace1->progs.fexit1);
+	if (!ASSERT_EQ(err, -EINVAL,
+		       "fentry1 update wrong expected_attach_type"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Program update should fail if type is a mismatch. */
+	err = bpf_link__update_program(skel_trace1->links.fentry1,
+				       skel_pkt1->progs.test_pkt_access);
+	if (!ASSERT_EQ(err, -EINVAL, "fentry1 update wrong type"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Program update should fail if program is incompatible */
+	err = bpf_link__update_program(skel_trace1->links.freplace1_bpf,
+				       skel_trace1->progs.freplace3_bpf);
+	if (!ASSERT_EQ(err, -EINVAL, "freplace1_bpf update incompatible"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Update with BPF_F_REPLACE should fail if old_prog_fd does not match
+	 * current link program.
+	 */
+	prog_fd = bpf_program__fd(skel_trace1->progs.fentry2);
+	link_fd = bpf_link__fd(skel_trace1->links.fentry1);
+	update_opts.old_prog_fd = bpf_program__fd(skel_trace1->progs.fentry2);
+	update_opts.flags = BPF_F_REPLACE;
+	err = bpf_link_update(link_fd, prog_fd, &update_opts);
+	if (!ASSERT_EQ(err, -EPERM, "BPF_F_REPLACE EPERM"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Do an in-place swap of program order using link updates.
+	 *
+	 * Update with BPF_F_REPLACE should succeed if old_prog_fd matches
+	 * current link program.
+	 * Update should succeed if the new program's dst_trampoline has been
+	 * cleared by a previous attach operation.
+	 */
+	update_opts.old_prog_fd = bpf_program__fd(skel_trace1->progs.fentry1);
+	err = bpf_link_update(link_fd, prog_fd, &update_opts);
+	if (!ASSERT_OK(err, "BPF_F_REPLACE"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry2,
+				       skel_trace1->progs.fentry1);
+	if (!ASSERT_OK(err, "fentry2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fmod_ret1,
+				       skel_trace1->progs.fmod_ret2);
+	if (!ASSERT_OK(err, "fmod_ret1 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fmod_ret2,
+				       skel_trace1->progs.fmod_ret1);
+	if (!ASSERT_OK(err, "fmod_ret2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit1,
+				       skel_trace1->progs.fexit2);
+	if (!ASSERT_OK(err, "fexit1 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit2,
+				       skel_trace1->progs.fexit1);
+	if (!ASSERT_OK(err, "fexit2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry1_bpf,
+				       skel_trace1->progs.fentry2_bpf);
+	if (!ASSERT_OK(err, "fentry1_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry2_bpf,
+				       skel_trace1->progs.fentry1_bpf);
+	if (!ASSERT_OK(err, "fentry2_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit1_bpf,
+				       skel_trace1->progs.fexit2_bpf);
+	if (!ASSERT_OK(err, "fexit1_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit2_bpf,
+				       skel_trace1->progs.fexit1_bpf);
+	if (!ASSERT_OK(err, "fexit2_bpf update"))
+		goto cleanup;
+	/* Only one freplace program can be attached at a time, so instead of
+	 * swapping the order as with fentry/fmod_ret/fexit just shuffle
+	 * freplace1_bpf and freplace_bpf2.
+	 */
+	err = bpf_link__destroy(skel_trace1->links.freplace1_bpf);
+	if (!ASSERT_OK(err, "freplace1_bpf destroy"))
+		goto cleanup;
+	skel_trace1->links.freplace1_bpf = NULL;
+	link = bpf_program__attach_trace(skel_trace1->progs.freplace2_bpf);
+	if (!ASSERT_OK_PTR(link, "attach freplace2_bpf"))
+		goto cleanup;
+	skel_trace1->links.freplace2_bpf = link;
+	err = bpf_link__update_program(skel_trace1->links.freplace2_bpf,
+				       skel_trace1->progs.freplace1_bpf);
+	if (!ASSERT_OK(err, "freplace2_bpf update"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace1, skel_pkt1, &expected_inverted))
+		goto cleanup;
+
+	/* Update should work when the new program's dst_trampoline points to
+	 * another trampoline or the same trampoline.
+	 */
+	skel_trace2 = prog_update_tracing__open();
+	if (!ASSERT_OK_PTR(skel_trace2, "skel_trace2"))
+		goto cleanup;
+	skel_pkt2 = test_pkt_access__open_and_load();
+	if (!ASSERT_OK_PTR(skel_pkt2, "skel_pkt2"))
+		goto cleanup;
+	prog_fd = bpf_program__fd(skel_pkt2->progs.test_pkt_access);
+	bpf_program__set_attach_target(skel_trace2->progs.fentry1_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace2->progs.fentry2_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace2->progs.fexit1_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace2->progs.fexit2_bpf, prog_fd,
+				       NULL);
+	bpf_program__set_attach_target(skel_trace2->progs.freplace1_bpf,
+				       prog_fd, "test_pkt_access_subprog3");
+	bpf_program__set_attach_target(skel_trace2->progs.freplace2_bpf,
+				       prog_fd, "test_pkt_access_subprog3");
+	bpf_program__set_attach_target(skel_trace2->progs.freplace3_bpf,
+				       prog_fd, "get_skb_ifindex");
+	err = prog_update_tracing__load(skel_trace2);
+	if (!ASSERT_OK(err, "skel_trace2 load"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry1,
+				       skel_trace2->progs.fentry1);
+	if (!ASSERT_OK(err, "fentry1 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry2,
+				       skel_trace2->progs.fentry2);
+	if (!ASSERT_OK(err, "fentry2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fmod_ret1,
+				       skel_trace2->progs.fmod_ret1);
+	if (!ASSERT_OK(err, "fmod_ret1 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fmod_ret2,
+				       skel_trace2->progs.fmod_ret2);
+	if (!ASSERT_OK(err, "fmod_ret2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit1,
+				       skel_trace2->progs.fexit1);
+	if (!ASSERT_OK(err, "fexit1 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit2,
+				       skel_trace2->progs.fexit2);
+	if (!ASSERT_OK(err, "fexit2 update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry1_bpf,
+				       skel_trace2->progs.fentry1_bpf);
+	if (!ASSERT_OK(err, "fentry1_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fentry2_bpf,
+				       skel_trace2->progs.fentry2_bpf);
+	if (!ASSERT_OK(err, "fentry2_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.freplace2_bpf,
+				       skel_trace2->progs.freplace1_bpf);
+	if (!ASSERT_OK(err, "freplace2_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit1_bpf,
+				       skel_trace2->progs.fexit1_bpf);
+	if (!ASSERT_OK(err, "fexit1_bpf update"))
+		goto cleanup;
+	err = bpf_link__update_program(skel_trace1->links.fexit2_bpf,
+				       skel_trace2->progs.fexit2_bpf);
+	if (!ASSERT_OK(err, "fexit2_bpf update"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace2, skel_pkt1, &expected_normal))
+		goto cleanup;
+
+	/* Update should work when the new program is the same as the current
+	 * program.
+	 */
+	err = bpf_link__update_program(skel_trace1->links.fentry1,
+				       skel_trace2->progs.fentry1);
+	if (!ASSERT_OK(err, "fentry1 update"))
+		goto cleanup;
+	if (!assert_program_order(skel_trace2, skel_pkt1, &expected_normal))
+		goto cleanup;
+cleanup:
+	prog_update_tracing__destroy(skel_trace1);
+	prog_update_tracing__destroy(skel_trace2);
+	test_pkt_access__destroy(skel_pkt1);
+	test_pkt_access__destroy(skel_pkt2);
+}
diff --git a/tools/testing/selftests/bpf/progs/prog_update_tracing.c b/tools/testing/selftests/bpf/progs/prog_update_tracing.c
new file mode 100644
index 000000000000..bdf314e28425
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/prog_update_tracing.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+__u64 sequence = 0;
+
+__u64 fentry1_seq = 0;
+__u64 fentry1_cookie = 0;
+SEC("fentry/bpf_modify_return_test")
+int BPF_PROG(fentry1, int a, __u64 b)
+{
+	fentry1_seq = ++sequence;
+	fentry1_cookie = bpf_get_attach_cookie(ctx);
+	return 0;
+}
+
+__u64 fentry2_seq = 0;
+__u64 fentry2_cookie = 0;
+SEC("fentry/bpf_modify_return_test")
+int BPF_PROG(fentry2, int a, __u64 b)
+{
+	fentry2_seq = ++sequence;
+	fentry2_cookie = bpf_get_attach_cookie(ctx);
+	return 0;
+}
+
+__u64 fmod_ret1_seq = 0;
+__u64 fmod_ret1_cookie = 0;
+SEC("fmod_ret/bpf_modify_return_test")
+int BPF_PROG(fmod_ret1, int a, int *b, int ret)
+{
+	fmod_ret1_seq = ++sequence;
+	fmod_ret1_cookie = bpf_get_attach_cookie(ctx);
+	return ret;
+}
+
+__u64 fmod_ret2_seq = 0;
+__u64 fmod_ret2_cookie = 0;
+SEC("fmod_ret/bpf_modify_return_test")
+int BPF_PROG(fmod_ret2, int a, int *b, int ret)
+{
+	fmod_ret2_seq = ++sequence;
+	fmod_ret2_cookie = bpf_get_attach_cookie(ctx);
+	return ret;
+}
+
+__u64 fexit1_seq = 0;
+__u64 fexit1_cookie = 0;
+SEC("fexit/bpf_modify_return_test")
+int BPF_PROG(fexit1, int a, __u64 b, int ret)
+{
+	fexit1_seq = ++sequence;
+	fexit1_cookie = bpf_get_attach_cookie(ctx);
+	return 0;
+}
+
+__u64 fexit2_seq = 0;
+__u64 fexit2_cookie = 0;
+SEC("fexit/bpf_modify_return_test")
+int BPF_PROG(fexit2, int a, __u64 b, int ret)
+{
+	fexit2_seq = ++sequence;
+	fexit2_cookie = bpf_get_attach_cookie(ctx);
+	return 0;
+}
+
+__u64 sequence_bpf = 0;
+
+__u64 fentry1_bpf_seq = 0;
+__u64 fentry1_bpf_cookie = 0;
+SEC("fentry/test_pkt_access")
+int fentry1_bpf(struct __sk_buff *skb)
+{
+	fentry1_bpf_seq = ++sequence_bpf;
+	fentry1_bpf_cookie = bpf_get_attach_cookie(skb);
+	return 0;
+}
+
+__u64 fentry2_bpf_seq = 0;
+__u64 fentry2_bpf_cookie = 0;
+SEC("fentry/test_pkt_access")
+int fentry2_bpf(struct __sk_buff *skb)
+{
+	fentry2_bpf_seq = ++sequence_bpf;
+	fentry2_bpf_cookie = bpf_get_attach_cookie(skb);
+	return 0;
+}
+
+__u64 freplace1_bpf_seq = 0;
+SEC("freplace/test_pkt_access_subprog3")
+int freplace1_bpf(int val, struct __sk_buff *skb)
+{
+	freplace1_bpf_seq = ++sequence_bpf;
+	return 0;
+}
+
+__u64 freplace2_bpf_seq = 0;
+SEC("freplace/test_pkt_access_subprog3")
+int freplace2_bpf(int val, struct __sk_buff *skb)
+{
+	freplace2_bpf_seq = ++sequence_bpf;
+	return 0;
+}
+
+SEC("freplace/get_skb_ifindex")
+int freplace3_bpf(int val, struct __sk_buff *skb, int var)
+{
+	return 0;
+}
+
+__u64 fexit1_bpf_seq = 0;
+__u64 fexit1_bpf_cookie = 0;
+SEC("fexit/test_pkt_access")
+int fexit1_bpf(struct __sk_buff *skb, int ret)
+{
+	fexit1_bpf_seq = ++sequence_bpf;
+	fexit1_bpf_cookie = bpf_get_attach_cookie(skb);
+	return 0;
+}
+
+__u64 fexit2_bpf_seq = 0;
+__u64 fexit2_bpf_cookie = 0;
+SEC("fexit/test_pkt_access")
+int fexit2_bpf(struct __sk_buff *skb, int ret)
+{
+	fexit2_bpf_seq = ++sequence_bpf;
+	fexit2_bpf_cookie = bpf_get_attach_cookie(skb);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.43.0

Re: [RFC PATCH bpf-next 0/7] bpf: Implement BPF_LINK_UPDATE for tracing links

[Alexei Starovoitov]

On Mon, Nov 17, 2025 at 4:53 PM Jordan Rife <jordan@jrife.io> wrote:
>
> Implement update_prog for bpf_tracing_link_lops to enable
> BPF_LINK_UPDATE for fentry, fexit, fmod_ret, freplace, etc. links.
>
> My initial motivation for this was to enable a use case where one
> process creates and owns links pointing to "hooks" within a tc, xdp, ...
> attachment and an external "plugin" loads freplace programs and updates
> links to these hooks. Aside from that though, it seemed like it could
> be useful to be able to atomically swap out the program associated with
> an freplace/fentry/fexit/fmod_ret link more generally.

I don't think we should burden the kernel with link_update for fentry/fexit.
bpf trampoline is already complex enough. I don't feel that
additional complexity is justified.

Re: [RFC PATCH bpf-next 0/7] bpf: Implement BPF_LINK_UPDATE for tracing links

[Jordan Rife]

On Fri, Nov 21, 2025 at 05:43:28PM -0800, Alexei Starovoitov wrote:
> On Mon, Nov 17, 2025 at 4:53 PM Jordan Rife <jordan@jrife.io> wrote:
> >
> > Implement update_prog for bpf_tracing_link_lops to enable
> > BPF_LINK_UPDATE for fentry, fexit, fmod_ret, freplace, etc. links.
> >
> > My initial motivation for this was to enable a use case where one
> > process creates and owns links pointing to "hooks" within a tc, xdp, ...
> > attachment and an external "plugin" loads freplace programs and updates
> > links to these hooks. Aside from that though, it seemed like it could
> > be useful to be able to atomically swap out the program associated with
> > an freplace/fentry/fexit/fmod_ret link more generally.
> 
> I don't think we should burden the kernel with link_update for fentry/fexit.
> bpf trampoline is already complex enough. I don't feel that
> additional complexity is justified.

OK. I could drop fentry/fexit from the series to avoid complexity with
the associated arch-specific stuff.

Jordan