[PATCH bpf-next v7 0/5] Support non-linear skbs for BPF_PROG_TEST_RUN

[PATCH bpf-next v7 0/5] Support non-linear skbs for BPF_PROG_TEST_RUN

[Paul Chaignon]

This patchset adds support for non-linear skbs when running tc programs
with BPF_PROG_TEST_RUN.

We've had multiple bugs in the past few years in Cilium caused by
missing calls to bpf_skb_pull_data(). Daniel suggested this new
BPF_PROG_TEST_RUN flag as a way to uncover these bugs in our BPF tests.

Changes in v7:
  - Refactor use of 'size' variable as suggested by Martin.
  - Support copying back the non-linear area to data_out.
  - Minor code changes for readability, suggested by Martin.
Changes in v6:
  - Disallow non-linear skb in prog_run_skb only for LWT programs
    instead of all non-L2 program types, on suggestion from Martin.
  - Reject non-null ctx->data and ctx->data_meta, as suggested by Amery.
  - Bound linear_size to 'PAGE_SIZE - headroom - tailroom' to be
    consistent with prog_run_xdp, as suggested by Martin.
  - Allocate exactly linear_size bytes in bpf_test_init, spotted by
    Martin.
  - Fix wrong conflict resolution on double-free fix, spotted by Amery.
  - Rebased.
Changes in v5:
  - Fix double free on data in first patch.
Changes in v4:
  - Per Martin's suggestion, follow the XDP code pattern and use
    bpf_test_init only to initialize the linear area. That way data is
    directly copied to the right areas and we avoid the call to
    __pskb_pull_tail.
  - Fixed outdated commit descriptions.
  - Rebased.
Changes in v3:
  - Dropped BPF_F_TEST_SKB_NON_LINEAR and used the ctx->data_end to
    determine if the user wants non-linear skb, as suggested by Amery.
  - Introduced a second commit with a bit of refactoring to allow for
    the above requested change.
  - Fix bug found by syzkaller on third commit.
  - Rebased.
Changes in v2:
  - Made the linear size configurable via ctx->data_end, as suggested
    by Amery.
  - Reworked the selftests to allow testing the configurable linear
    size.
  - Fix warnings reported by kernel test robot on first commit.
  - Rebased.

Paul Chaignon (5):
  bpf: Refactor cleanup of bpf_prog_test_run_skb
  bpf: Reorder bpf_prog_test_run_skb initialization
  bpf: Craft non-linear skbs in BPF_PROG_TEST_RUN
  selftests/bpf: Support non-linear flag in test loader
  selftests/bpf: Test direct packet access on non-linear skbs

 net/bpf/test_run.c                            | 141 +++++++++++++-----
 tools/testing/selftests/bpf/progs/bpf_misc.h  |   4 +
 .../bpf/progs/verifier_direct_packet_access.c |  59 ++++++++
 tools/testing/selftests/bpf/test_loader.c     |  19 ++-
 4 files changed, 182 insertions(+), 41 deletions(-)

-- 
2.43.0

[PATCH bpf-next v7 1/5] bpf: Refactor cleanup of bpf_prog_test_run_skb

[Paul Chaignon]

This bit of refactoring aims to simplify how we free memory in
bpf_prog_test_run_skb to avoid code duplication.

Tested-by: syzbot@syzkaller.appspotmail.com
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 net/bpf/test_run.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index dfb03ee0bb62..a39b26739a1e 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -990,10 +990,10 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	u32 size = kattr->test.data_size_in;
 	u32 repeat = kattr->test.repeat;
 	struct __sk_buff *ctx = NULL;
+	struct sk_buff *skb = NULL;
+	struct sock *sk = NULL;
 	u32 retval, duration;
 	int hh_len = ETH_HLEN;
-	struct sk_buff *skb;
-	struct sock *sk;
 	void *data;
 	int ret;
 
@@ -1012,8 +1012,9 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 
 	ctx = bpf_ctx_init(kattr, sizeof(struct __sk_buff));
 	if (IS_ERR(ctx)) {
-		kfree(data);
-		return PTR_ERR(ctx);
+		ret = PTR_ERR(ctx);
+		ctx = NULL;
+		goto out;
 	}
 
 	switch (prog->type) {
@@ -1033,21 +1034,20 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 
 	sk = sk_alloc(net, AF_UNSPEC, GFP_USER, &bpf_dummy_proto, 1);
 	if (!sk) {
-		kfree(data);
-		kfree(ctx);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out;
 	}
 	sock_init_data(NULL, sk);
 
 	skb = slab_build_skb(data);
 	if (!skb) {
-		kfree(data);
-		kfree(ctx);
-		sk_free(sk);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out;
 	}
 	skb->sk = sk;
 
+	data = NULL; /* data released via kfree_skb */
+
 	skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
 	__skb_put(skb, size);
 
@@ -1142,7 +1142,9 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	if (dev && dev != net->loopback_dev)
 		dev_put(dev);
 	kfree_skb(skb);
-	sk_free(sk);
+	kfree(data);
+	if (sk)
+		sk_free(sk);
 	kfree(ctx);
 	return ret;
 }
-- 
2.43.0

[PATCH bpf-next v7 2/5] bpf: Reorder bpf_prog_test_run_skb initialization

[Paul Chaignon]

This patch reorders the initialization of bpf_prog_test_run_skb to
simplify the subsequent patch. Program types are checked first, followed
by the ctx init, and finally the data init. With the subsequent patch,
program types and the ctx init provide information that is used in the
data init. Thus, we need the data init to happen last.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 net/bpf/test_run.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index a39b26739a1e..b9b49d0c7014 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1004,19 +1004,6 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	if (size < ETH_HLEN)
 		return -EINVAL;
 
-	data = bpf_test_init(kattr, kattr->test.data_size_in,
-			     size, NET_SKB_PAD + NET_IP_ALIGN,
-			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
-	if (IS_ERR(data))
-		return PTR_ERR(data);
-
-	ctx = bpf_ctx_init(kattr, sizeof(struct __sk_buff));
-	if (IS_ERR(ctx)) {
-		ret = PTR_ERR(ctx);
-		ctx = NULL;
-		goto out;
-	}
-
 	switch (prog->type) {
 	case BPF_PROG_TYPE_SCHED_CLS:
 	case BPF_PROG_TYPE_SCHED_ACT:
@@ -1032,6 +1019,19 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 		break;
 	}
 
+	ctx = bpf_ctx_init(kattr, sizeof(struct __sk_buff));
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	data = bpf_test_init(kattr, kattr->test.data_size_in,
+			     size, NET_SKB_PAD + NET_IP_ALIGN,
+			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
+	if (IS_ERR(data)) {
+		ret = PTR_ERR(data);
+		data = NULL;
+		goto out;
+	}
+
 	sk = sk_alloc(net, AF_UNSPEC, GFP_USER, &bpf_dummy_proto, 1);
 	if (!sk) {
 		ret = -ENOMEM;
-- 
2.43.0

[PATCH bpf-next v7 3/5] bpf: Craft non-linear skbs in BPF_PROG_TEST_RUN

[Paul Chaignon]

This patch adds support for crafting non-linear skbs in BPF test runs
for tc programs. The size of the linear area is given by ctx->data_end,
with a minimum of ETH_HLEN always pulled in the linear area. If ctx or
ctx->data_end are null, a linear skb is used.

This is particularly useful to test support for non-linear skbs in large
codebases such as Cilium. We've had multiple bugs in the past few years
where we were missing calls to bpf_skb_pull_data(). This support in
BPF_PROG_TEST_RUN would allow us to automatically cover this case in our
BPF tests.

LWT program types are currently excluded in this patch. Allowing
non-linear skbs for these programs would require a bit more care because
they are able to call helpers (ex., bpf_clone_redirect, bpf_redirect)
that themselves call eth_type_trans(). eth_type_trans() assumes there
are at least ETH_HLEN bytes in the linear area. That may not be true
for LWT programs as we already pulled the L2 header via the
eth_type_trans() call in bpf_prog_test_run_skb().

In addition to the selftests introduced later in the series, this patch
was tested by enabling non-linear skbs for all tc selftests programs
and checking test failures were expected.

Tested-by: syzbot@syzkaller.appspotmail.com
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 net/bpf/test_run.c | 101 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 81 insertions(+), 20 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index b9b49d0c7014..6ac393c95962 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -447,7 +447,7 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
 
 static int bpf_test_finish(const union bpf_attr *kattr,
 			   union bpf_attr __user *uattr, const void *data,
-			   struct skb_shared_info *sinfo, u32 size,
+			   struct skb_shared_info *sinfo, u32 size, u32 frag_size,
 			   u32 retval, u32 duration)
 {
 	void __user *data_out = u64_to_user_ptr(kattr->test.data_out);
@@ -464,7 +464,7 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 	}
 
 	if (data_out) {
-		int len = sinfo ? copy_size - sinfo->xdp_frags_size : copy_size;
+		int len = sinfo ? copy_size - frag_size : copy_size;
 
 		if (len < 0) {
 			err = -ENOSPC;
@@ -910,6 +910,12 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct __sk_buff *__skb)
 	/* cb is allowed */
 
 	if (!range_is_zero(__skb, offsetofend(struct __sk_buff, cb),
+			   offsetof(struct __sk_buff, data_end)))
+		return -EINVAL;
+
+	/* data_end is allowed, but not copied to skb */
+
+	if (!range_is_zero(__skb, offsetofend(struct __sk_buff, data_end),
 			   offsetof(struct __sk_buff, tstamp)))
 		return -EINVAL;
 
@@ -984,10 +990,12 @@ static struct proto bpf_dummy_proto = {
 int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr)
 {
-	bool is_l2 = false, is_direct_pkt_access = false;
+	bool is_l2 = false, is_direct_pkt_access = false, is_lwt = false;
+	u32 tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 	struct net *net = current->nsproxy->net_ns;
 	struct net_device *dev = net->loopback_dev;
-	u32 size = kattr->test.data_size_in;
+	u32 headroom = NET_SKB_PAD + NET_IP_ALIGN;
+	u32 linear_sz = kattr->test.data_size_in;
 	u32 repeat = kattr->test.repeat;
 	struct __sk_buff *ctx = NULL;
 	struct sk_buff *skb = NULL;
@@ -1001,17 +1009,20 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	    kattr->test.cpu || kattr->test.batch_size)
 		return -EINVAL;
 
-	if (size < ETH_HLEN)
+	if (kattr->test.data_size_in < ETH_HLEN)
 		return -EINVAL;
 
 	switch (prog->type) {
 	case BPF_PROG_TYPE_SCHED_CLS:
 	case BPF_PROG_TYPE_SCHED_ACT:
+		is_direct_pkt_access = true;
 		is_l2 = true;
-		fallthrough;
+		break;
 	case BPF_PROG_TYPE_LWT_IN:
 	case BPF_PROG_TYPE_LWT_OUT:
 	case BPF_PROG_TYPE_LWT_XMIT:
+		is_lwt = true;
+		fallthrough;
 	case BPF_PROG_TYPE_CGROUP_SKB:
 		is_direct_pkt_access = true;
 		break;
@@ -1023,9 +1034,24 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	data = bpf_test_init(kattr, kattr->test.data_size_in,
-			     size, NET_SKB_PAD + NET_IP_ALIGN,
-			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
+	if (ctx) {
+		if (ctx->data_end > kattr->test.data_size_in || ctx->data || ctx->data_meta) {
+			ret = -EINVAL;
+			goto out;
+		}
+		if (ctx->data_end) {
+			/* Non-linear LWT test_run is unsupported for now. */
+			if (is_lwt) {
+				ret = -EINVAL;
+				goto out;
+			}
+			linear_sz = max(ETH_HLEN, ctx->data_end);
+		}
+	}
+
+	linear_sz = min_t(u32, linear_sz, PAGE_SIZE - headroom - tailroom);
+
+	data = bpf_test_init(kattr, linear_sz, linear_sz, headroom, tailroom);
 	if (IS_ERR(data)) {
 		ret = PTR_ERR(data);
 		data = NULL;
@@ -1049,7 +1075,43 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	data = NULL; /* data released via kfree_skb */
 
 	skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
-	__skb_put(skb, size);
+	__skb_put(skb, linear_sz);
+
+	if (unlikely(kattr->test.data_size_in > linear_sz)) {
+		void __user *data_in = u64_to_user_ptr(kattr->test.data_in);
+		struct skb_shared_info *sinfo = skb_shinfo(skb);
+		u32 copied = linear_sz;
+
+		while (copied < kattr->test.data_size_in) {
+			struct page *page;
+			u32 data_len;
+
+			if (sinfo->nr_frags == MAX_SKB_FRAGS) {
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			page = alloc_page(GFP_KERNEL);
+			if (!page) {
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			data_len = min_t(u32, kattr->test.data_size_in - copied,
+					 PAGE_SIZE);
+			skb_fill_page_desc(skb, sinfo->nr_frags, page, 0, data_len);
+
+			if (copy_from_user(page_address(page), data_in + copied,
+					   data_len)) {
+				ret = -EFAULT;
+				goto out;
+			}
+			skb->data_len += data_len;
+			skb->truesize += PAGE_SIZE;
+			skb->len += data_len;
+			copied += data_len;
+		}
+	}
 
 	if (ctx && ctx->ifindex > 1) {
 		dev = dev_get_by_index(net, ctx->ifindex);
@@ -1129,12 +1191,11 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 
 	convert_skb_to___skb(skb, ctx);
 
-	size = skb->len;
-	/* bpf program can never convert linear skb to non-linear */
-	if (WARN_ON_ONCE(skb_is_nonlinear(skb)))
-		size = skb_headlen(skb);
-	ret = bpf_test_finish(kattr, uattr, skb->data, NULL, size, retval,
-			      duration);
+	if (skb_is_nonlinear(skb))
+		/* bpf program can never convert linear skb to non-linear */
+		WARN_ON_ONCE(linear_sz == kattr->test.data_size_in);
+	ret = bpf_test_finish(kattr, uattr, skb->data, skb_shinfo(skb), skb->len,
+			      skb->data_len, retval, duration);
 	if (!ret)
 		ret = bpf_ctx_finish(kattr, uattr, ctx,
 				     sizeof(struct __sk_buff));
@@ -1342,7 +1403,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 		goto out;
 
 	size = xdp.data_end - xdp.data_meta + sinfo->xdp_frags_size;
-	ret = bpf_test_finish(kattr, uattr, xdp.data_meta, sinfo, size,
+	ret = bpf_test_finish(kattr, uattr, xdp.data_meta, sinfo, size, sinfo->xdp_frags_size,
 			      retval, duration);
 	if (!ret)
 		ret = bpf_ctx_finish(kattr, uattr, ctx,
@@ -1433,7 +1494,7 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
 		goto out;
 
 	ret = bpf_test_finish(kattr, uattr, &flow_keys, NULL,
-			      sizeof(flow_keys), retval, duration);
+			      sizeof(flow_keys), 0, retval, duration);
 	if (!ret)
 		ret = bpf_ctx_finish(kattr, uattr, user_ctx,
 				     sizeof(struct bpf_flow_keys));
@@ -1534,7 +1595,7 @@ int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog, const union bpf_attr *kat
 		user_ctx->cookie = sock_gen_cookie(ctx.selected_sk);
 	}
 
-	ret = bpf_test_finish(kattr, uattr, NULL, NULL, 0, retval, duration);
+	ret = bpf_test_finish(kattr, uattr, NULL, NULL, 0, 0, retval, duration);
 	if (!ret)
 		ret = bpf_ctx_finish(kattr, uattr, user_ctx, sizeof(*user_ctx));
 
@@ -1734,7 +1795,7 @@ int bpf_prog_test_run_nf(struct bpf_prog *prog,
 	if (ret)
 		goto out;
 
-	ret = bpf_test_finish(kattr, uattr, NULL, NULL, 0, retval, duration);
+	ret = bpf_test_finish(kattr, uattr, NULL, NULL, 0, 0, retval, duration);
 
 out:
 	kfree(user_ctx);
-- 
2.43.0

Re: [PATCH bpf-next v7 3/5] bpf: Craft non-linear skbs in BPF_PROG_TEST_RUN

[Martin KaFai Lau]

On 10/9/25 7:02 AM, Paul Chaignon wrote:
> This patch adds support for crafting non-linear skbs in BPF test runs
> for tc programs. The size of the linear area is given by ctx->data_end,
> with a minimum of ETH_HLEN always pulled in the linear area. If ctx or
> ctx->data_end are null, a linear skb is used.
> 
> This is particularly useful to test support for non-linear skbs in large
> codebases such as Cilium. We've had multiple bugs in the past few years
> where we were missing calls to bpf_skb_pull_data(). This support in
> BPF_PROG_TEST_RUN would allow us to automatically cover this case in our
> BPF tests.
> 
> LWT program types are currently excluded in this patch. Allowing
> non-linear skbs for these programs would require a bit more care because
> they are able to call helpers (ex., bpf_clone_redirect, bpf_redirect)
> that themselves call eth_type_trans(). eth_type_trans() assumes there
> are at least ETH_HLEN bytes in the linear area. That may not be true
> for LWT programs as we already pulled the L2 header via the
> eth_type_trans() call in bpf_prog_test_run_skb().

Thanks for the details on lwt.

> @@ -1023,9 +1034,24 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>   	if (IS_ERR(ctx))
>   		return PTR_ERR(ctx);
>   
> -	data = bpf_test_init(kattr, kattr->test.data_size_in,
> -			     size, NET_SKB_PAD + NET_IP_ALIGN,
> -			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
> +	if (ctx) {
> +		if (ctx->data_end > kattr->test.data_size_in || ctx->data || ctx->data_meta) {
> +			ret = -EINVAL;
> +			goto out;

The "void *data" is still not initialized. There is a kfree(data) at "out:".

> +		}
> +		if (ctx->data_end) {
> +			/* Non-linear LWT test_run is unsupported for now. */
> +			if (is_lwt) {
> +				ret = -EINVAL;
> +				goto out;

same here.

pw-bot: cr

[PATCH bpf-next v7 4/5] selftests/bpf: Support non-linear flag in test loader

[Paul Chaignon]

This patch adds support for a new tag __linear_size in the test loader,
to specify the size of the linear area in case of non-linear skbs. If
the tag is absent or null, a linear skb is crafted.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 tools/testing/selftests/bpf/progs/bpf_misc.h  |  4 ++++
 .../bpf/progs/verifier_direct_packet_access.c |  1 +
 tools/testing/selftests/bpf/test_loader.c     | 19 +++++++++++++++++--
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
index a7a1a684eed1..c9bfbe1bafc1 100644
--- a/tools/testing/selftests/bpf/progs/bpf_misc.h
+++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
@@ -126,6 +126,9 @@
  *                   Several __arch_* annotations could be specified at once.
  *                   When test case is not run on current arch it is marked as skipped.
  * __caps_unpriv     Specify the capabilities that should be set when running the test.
+ *
+ * __linear_size     Specify the size of the linear area of non-linear skbs, or
+ *                   0 for linear skbs.
  */
 #define __msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_msg=" XSTR(__COUNTER__) "=" msg)))
 #define __not_msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_not_msg=" XSTR(__COUNTER__) "=" msg)))
@@ -159,6 +162,7 @@
 #define __stderr_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_stderr_unpriv=" XSTR(__COUNTER__) "=" msg)))
 #define __stdout(msg)		__attribute__((btf_decl_tag("comment:test_expect_stdout=" XSTR(__COUNTER__) "=" msg)))
 #define __stdout_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_stdout_unpriv=" XSTR(__COUNTER__) "=" msg)))
+#define __linear_size(sz)	__attribute__((btf_decl_tag("comment:test_linear_size=" XSTR(sz))))
 
 /* Define common capabilities tested using __caps_unpriv */
 #define CAP_NET_ADMIN		12
diff --git a/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c b/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
index 28b602ac9cbe..a61897e01a50 100644
--- a/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
+++ b/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Converted from tools/testing/selftests/bpf/verifier/direct_packet_access.c */
 
+#include <linux/if_ether.h>
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c
index 74ecc281bb8c..690181617f04 100644
--- a/tools/testing/selftests/bpf/test_loader.c
+++ b/tools/testing/selftests/bpf/test_loader.c
@@ -43,6 +43,7 @@
 #define TEST_TAG_EXPECT_STDERR_PFX_UNPRIV "comment:test_expect_stderr_unpriv="
 #define TEST_TAG_EXPECT_STDOUT_PFX "comment:test_expect_stdout="
 #define TEST_TAG_EXPECT_STDOUT_PFX_UNPRIV "comment:test_expect_stdout_unpriv="
+#define TEST_TAG_LINEAR_SIZE "comment:test_linear_size="
 
 /* Warning: duplicated in bpf_misc.h */
 #define POINTER_VALUE	0xbadcafe
@@ -89,6 +90,7 @@ struct test_spec {
 	int mode_mask;
 	int arch_mask;
 	int load_mask;
+	int linear_sz;
 	bool auxiliary;
 	bool valid;
 };
@@ -633,6 +635,11 @@ static int parse_test_spec(struct test_loader *tester,
 					      &spec->unpriv.stdout);
 			if (err)
 				goto cleanup;
+		} else if (str_has_pfx(s, TEST_TAG_LINEAR_SIZE)) {
+			val = s + sizeof(TEST_TAG_LINEAR_SIZE) - 1;
+			err = parse_int(val, &spec->linear_sz, "test linear size");
+			if (err)
+				goto cleanup;
 		}
 	}
 
@@ -1007,10 +1014,11 @@ static bool is_unpriv_capable_map(struct bpf_map *map)
 	}
 }
 
-static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts)
+static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts, int linear_sz)
 {
 	__u8 tmp_out[TEST_DATA_LEN << 2] = {};
 	__u8 tmp_in[TEST_DATA_LEN] = {};
+	struct __sk_buff ctx = {};
 	int err, saved_errno;
 	LIBBPF_OPTS(bpf_test_run_opts, topts,
 		.data_in = tmp_in,
@@ -1020,6 +1028,12 @@ static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts)
 		.repeat = 1,
 	);
 
+	if (linear_sz) {
+		ctx.data_end = linear_sz;
+		topts.ctx_in = &ctx;
+		topts.ctx_size_in = sizeof(ctx);
+	}
+
 	if (empty_opts) {
 		memset(&topts, 0, sizeof(struct bpf_test_run_opts));
 		topts.sz = sizeof(struct bpf_test_run_opts);
@@ -1269,7 +1283,8 @@ void run_subtest(struct test_loader *tester,
 		}
 
 		err = do_prog_test_run(bpf_program__fd(tprog), &retval,
-				       bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false);
+				       bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false,
+				       spec->linear_sz);
 		if (!err && retval != subspec->retval && subspec->retval != POINTER_VALUE) {
 			PRINT_FAIL("Unexpected retval: %d != %d\n", retval, subspec->retval);
 			goto tobj_cleanup;
-- 
2.43.0

Re: [PATCH bpf-next v7 4/5] selftests/bpf: Support non-linear flag in test loader

[Martin KaFai Lau]

On 10/9/25 7:02 AM, Paul Chaignon wrote:
> @@ -633,6 +635,11 @@ static int parse_test_spec(struct test_loader *tester,
>   					      &spec->unpriv.stdout);
>   			if (err)
>   				goto cleanup;
> +		} else if (str_has_pfx(s, TEST_TAG_LINEAR_SIZE)) {
> +			val = s + sizeof(TEST_TAG_LINEAR_SIZE) - 1;
> +			err = parse_int(val, &spec->linear_sz, "test linear size");
> +			if (err)
> +				goto cleanup;
>   		}
>   	}
>   
> @@ -1007,10 +1014,11 @@ static bool is_unpriv_capable_map(struct bpf_map *map)
>   	}
>   }
>   
> -static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts)
> +static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts, int linear_sz)
>   {
>   	__u8 tmp_out[TEST_DATA_LEN << 2] = {};
>   	__u8 tmp_in[TEST_DATA_LEN] = {};
> +	struct __sk_buff ctx = {};

since it needs a re-spin...

not all prog type uses "struct __sk_buff". linear_sz could be useful for xdp 
also but it also needs a different struct. This is pretty much "tc" and 
"cgroup_skb" only for now. How about error out earlier in the parse_test_spec? I 
think the bpf_program__type() should already be available at the parse_test_spec().

>   	int err, saved_errno;
>   	LIBBPF_OPTS(bpf_test_run_opts, topts,
>   		.data_in = tmp_in,
> @@ -1020,6 +1028,12 @@ static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts)
>   		.repeat = 1,
>   	);
>   
> +	if (linear_sz) {
> +		ctx.data_end = linear_sz;
> +		topts.ctx_in = &ctx;
> +		topts.ctx_size_in = sizeof(ctx);
> +	}
> +

[PATCH bpf-next v7 5/5] selftests/bpf: Test direct packet access on non-linear skbs

[Paul Chaignon]

This patch adds new selftests in the direct packet access suite, to
cover the non-linear case. The first six tests cover the behavior of
the bounds check with a non-linear skb. The last test adds a call to
bpf_skb_pull_data() to be able to access the packet.

Note that the size of the linear area includes the L2 header, but for
some program types like cgroup_skb, ctx->data points to the L3 header.
Therefore, a linear area of 22 bytes will have only 8 bytes accessible
to the BPF program (22 - ETH_HLEN). For that reason, the cgroup_skb test
cases access the packet at an offset of 8 bytes.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 .../bpf/progs/verifier_direct_packet_access.c | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c b/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
index a61897e01a50..911caa8fd1b7 100644
--- a/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
+++ b/tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c
@@ -801,4 +801,62 @@ l0_%=:	/* exit(0) */					\
 	: __clobber_all);
 }
 
+#define access_test_non_linear(name, type, desc, retval, linear_sz, off)			\
+	SEC(type)										\
+	__description("direct packet access: " #name " (non-linear, " type ", " desc ")")	\
+	__success __retval(retval)								\
+	__linear_size(linear_sz)								\
+	__naked void access_non_linear_##name(void)						\
+	{											\
+		asm volatile ("									\
+		r2 = *(u32*)(r1 + %[skb_data]);							\
+		r3 = *(u32*)(r1 + %[skb_data_end]);						\
+		r0 = r2;									\
+		r0 += %[offset];								\
+		if r0 > r3 goto l0_%=;								\
+		r0 = *(u8*)(r0 - 1);								\
+		r0 = 0;										\
+		exit;										\
+	l0_%=:	r0 = 1;										\
+		exit;										\
+	"	:										\
+		: __imm_const(skb_data, offsetof(struct __sk_buff, data)),			\
+		  __imm_const(skb_data_end, offsetof(struct __sk_buff, data_end)),		\
+		  __imm_const(offset, off)							\
+		: __clobber_all);								\
+	}
+
+access_test_non_linear(test31, "tc", "too short eth", 1, ETH_HLEN, 22);
+access_test_non_linear(test32, "tc", "too short 1", 1, 1, 22);
+access_test_non_linear(test33, "tc", "long enough", 0, 22, 22);
+access_test_non_linear(test34, "cgroup_skb/ingress", "too short eth", 1, ETH_HLEN, 8);
+access_test_non_linear(test35, "cgroup_skb/ingress", "too short 1", 1, 1, 8);
+access_test_non_linear(test36, "cgroup_skb/ingress", "long enough", 0, 22, 8);
+
+SEC("tc")
+__description("direct packet access: test37 (non-linear, linearized)")
+__success __retval(0)
+__linear_size(ETH_HLEN)
+__naked void access_non_linear_linearized(void)
+{
+	asm volatile ("				\
+	r6 = r1;				\
+	r2 = 22;				\
+	call %[bpf_skb_pull_data];		\
+	r2 = *(u32*)(r6 + %[skb_data]);		\
+	r3 = *(u32*)(r6 + %[skb_data_end]);	\
+	r0 = r2;				\
+	r0 += 22;				\
+	if r0 > r3 goto l0_%=;			\
+	r0 = *(u8*)(r0 - 1);			\
+	exit;					\
+l0_%=:	r0 = 1;					\
+	exit;					\
+"	:
+	: __imm(bpf_skb_pull_data),
+	  __imm_const(skb_data, offsetof(struct __sk_buff, data)),
+	  __imm_const(skb_data_end, offsetof(struct __sk_buff, data_end))
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0