Commit 34cc0b33 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Alexei Starovoitov
Browse files

xdp: Xdp_frame add member frame_sz and handle in convert_to_xdp_frame 



Use hole in struct xdp_frame, when adding member frame_sz, which keeps
same sizeof struct (32 bytes)

Drivers ixgbe and sfc had bug cases where the necessary/expected
tailroom was not reserved. This can lead to some hard to catch memory
corruption issues. Having the drivers frame_sz this can be detected when
packet length/end via xdp->data_end exceed the xdp_data_hard_end
pointer, which accounts for the reserved the tailroom.

When detecting this driver issue, simply fail the conversion with NULL,
which results in feedback to driver (failing xdp_do_redirect()) causing
driver to drop packet. Given the lack of consistent XDP stats, this can
be hard to troubleshoot. And given this is a driver bug, we want to
generate some more noise in form of a WARN stack dump (to ID the driver
code that inlined convert_to_xdp_frame).

Inlining the WARN macro is problematic, because it adds an asm
instruction (on Intel CPUs ud2) what influence instruction cache
prefetching. Thus, introduce xdp_warn and macro XDP_WARN, to avoid this
and at the same time make identifying the function and line of this
inlined function easier.

Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158945337313.97035.10015729316710496600.stgit@firesoul
parent a075767b

include/net/xdp.h

+13 −1
Original line number Diff line number Diff line
@@ -89,7 +89,8 @@ struct xdp_frame { 
	void *data;

	u16 len;

	u16 headroom;

	u16 metasize;

	u32 metasize:8;

	u32 frame_sz:24;

	/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,

	 * while mem info is valid on remote CPU.

	 */
@@ -104,6 +105,10 @@ static inline void xdp_scrub_frame(struct xdp_frame *frame) 
	frame->dev_rx = NULL;

}



/* Avoids inlining WARN macro in fast-path */

void xdp_warn(const char *msg, const char *func, const int line);

#define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__)



struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);



/* Convert xdp_buff to xdp_frame */
@@ -124,6 +129,12 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp) 
	if (unlikely((headroom - metasize) < sizeof(*xdp_frame)))

		return NULL;



	/* Catch if driver didn't reserve tailroom for skb_shared_info */

	if (unlikely(xdp->data_end > xdp_data_hard_end(xdp))) {

		XDP_WARN("Driver BUG: missing reserved tailroom");

		return NULL;

	}



	/* Store info in top of packet */

	xdp_frame = xdp->data_hard_start;
@@ -131,6 +142,7 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp) 
	xdp_frame->len  = xdp->data_end - xdp->data;

	xdp_frame->headroom = headroom - sizeof(*xdp_frame);

	xdp_frame->metasize = metasize;

	xdp_frame->frame_sz = xdp->frame_sz;



	/* rxq only valid until napi_schedule ends, convert to xdp_mem_info */

	xdp_frame->mem = xdp->rxq->mem;

net/core/xdp.c

+8 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/slab.h>

#include <linux/idr.h>

#include <linux/rhashtable.h>

#include <linux/bug.h>

#include <net/page_pool.h>



#include <net/xdp.h>
@@ -496,3 +497,10 @@ struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp) 
	return xdpf;

}

EXPORT_SYMBOL_GPL(xdp_convert_zc_to_xdp_frame);



/* Used by XDP_WARN macro, to avoid inlining WARN() in fast-path */

void xdp_warn(const char *msg, const char *func, const int line)

{

	WARN(1, "XDP_WARN: %s(line:%d): %s\n", func, line, msg);

};

EXPORT_SYMBOL_GPL(xdp_warn);

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