From: Alexander Lobakin aleksander.lobakin@intel.com
[ Upstream commit 6c20822fada1b8adb77fa450d03a0d449686a4a9 ]
&xdp_buff and &xdp_frame are bound in a way that
xdp_buff->data_hard_start == xdp_frame
It's always the case and e.g. xdp_convert_buff_to_frame() relies on this. IOW, the following:
for (u32 i = 0; i < 0xdead; i++) { xdpf = xdp_convert_buff_to_frame(&xdp); xdp_convert_frame_to_buff(xdpf, &xdp); }
shouldn't ever modify @xdpf's contents or the pointer itself. However, "live packet" code wrongly treats &xdp_frame as part of its context placed *before* the data_hard_start. With such flow, data_hard_start is sizeof(*xdpf) off to the right and no longer points to the XDP frame.
Instead of replacing `sizeof(ctx)` with `offsetof(ctx, xdpf)` in several places and praying that there are no more miscalcs left somewhere in the code, unionize ::frm with ::data in a flex array, so that both starts pointing to the actual data_hard_start and the XDP frame actually starts being a part of it, i.e. a part of the headroom, not the context. A nice side effect is that the maximum frame size for this mode gets increased by 40 bytes, as xdp_buff::frame_sz includes everything from data_hard_start (-> includes xdpf already) to the end of XDP/skb shared info. Also update %MAX_PKT_SIZE accordingly in the selftests code. Leave it hardcoded for 64 bit && 4k pages, it can be made more flexible later on.
Minor: align `&head->data` with how `head->frm` is assigned for consistency. Minor #2: rename 'frm' to 'frame' in &xdp_page_head while at it for clarity.
(was found while testing XDP traffic generator on ice, which calls xdp_convert_frame_to_buff() for each XDP frame)
Fixes: b530e9e1063e ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN") Acked-by: Toke Høiland-Jørgensen toke@redhat.com Signed-off-by: Alexander Lobakin aleksander.lobakin@intel.com Link: https://lore.kernel.org/r/20230215185440.4126672-1-aleksander.lobakin@intel.... Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/bpf/test_run.c | 29 +++++++++++++++---- .../bpf/prog_tests/xdp_do_redirect.c | 7 +++-- 2 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 6094ef7cffcd2..cd3d713251a26 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -97,8 +97,11 @@ static bool bpf_test_timer_continue(struct bpf_test_timer *t, int iterations, struct xdp_page_head { struct xdp_buff orig_ctx; struct xdp_buff ctx; - struct xdp_frame frm; - u8 data[]; + union { + /* ::data_hard_start starts here */ + DECLARE_FLEX_ARRAY(struct xdp_frame, frame); + DECLARE_FLEX_ARRAY(u8, data); + }; };
struct xdp_test_data { @@ -116,6 +119,20 @@ struct xdp_test_data { #define TEST_XDP_FRAME_SIZE (PAGE_SIZE - sizeof(struct xdp_page_head)) #define TEST_XDP_MAX_BATCH 256
+#if BITS_PER_LONG == 64 && PAGE_SIZE == SZ_4K +/* tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c:%MAX_PKT_SIZE + * must be updated accordingly when any of these changes, otherwise BPF + * selftests will fail. + */ +#ifdef __s390x__ +#define TEST_MAX_PKT_SIZE 3216 +#else +#define TEST_MAX_PKT_SIZE 3408 +#endif +static_assert(SKB_WITH_OVERHEAD(TEST_XDP_FRAME_SIZE - XDP_PACKET_HEADROOM) == + TEST_MAX_PKT_SIZE); +#endif + static void xdp_test_run_init_page(struct page *page, void *arg) { struct xdp_page_head *head = phys_to_virt(page_to_phys(page)); @@ -132,8 +149,8 @@ static void xdp_test_run_init_page(struct page *page, void *arg) headroom -= meta_len;
new_ctx = &head->ctx; - frm = &head->frm; - data = &head->data; + frm = head->frame; + data = head->data; memcpy(data + headroom, orig_ctx->data_meta, frm_len);
xdp_init_buff(new_ctx, TEST_XDP_FRAME_SIZE, &xdp->rxq); @@ -223,7 +240,7 @@ static void reset_ctx(struct xdp_page_head *head) head->ctx.data = head->orig_ctx.data; head->ctx.data_meta = head->orig_ctx.data_meta; head->ctx.data_end = head->orig_ctx.data_end; - xdp_update_frame_from_buff(&head->ctx, &head->frm); + xdp_update_frame_from_buff(&head->ctx, head->frame); }
static int xdp_recv_frames(struct xdp_frame **frames, int nframes, @@ -285,7 +302,7 @@ static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog, head = phys_to_virt(page_to_phys(page)); reset_ctx(head); ctx = &head->ctx; - frm = &head->frm; + frm = head->frame; xdp->frame_cnt++;
act = bpf_prog_run_xdp(prog, ctx); diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c index 15ad336691613..33ae63c01461a 100644 --- a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c +++ b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c @@ -63,12 +63,13 @@ static int attach_tc_prog(struct bpf_tc_hook *hook, int fd) }
/* The maximum permissible size is: PAGE_SIZE - sizeof(struct xdp_page_head) - - * sizeof(struct skb_shared_info) - XDP_PACKET_HEADROOM = 3368 bytes + * SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - XDP_PACKET_HEADROOM = + * 3408 bytes for 64-byte cacheline and 3216 for 256-byte one. */ #if defined(__s390x__) -#define MAX_PKT_SIZE 3176 +#define MAX_PKT_SIZE 3216 #else -#define MAX_PKT_SIZE 3368 +#define MAX_PKT_SIZE 3408 #endif static void test_max_pkt_size(int fd) {