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xdp: Xdp_frame add member frame_sz and handle in convert_to_xdp_frame

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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: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158945337313.97035.10015729316710496600.stgit@firesoul
This commit is contained in:
Jesper Dangaard Brouer 2020-05-14 12:49:33 +02:00 committed by Alexei Starovoitov
parent a075767bbd
commit 34cc0b338a
2 changed files with 21 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/net/xdp.h
View File

@ -89,7 +89,8 @@ struct xdp_frame {
void *data; void *data;
u16 len; u16 len;
u16 headroom; u16 headroom;
u16 metasize; u32 metasize:8;
u32 frame_sz:24;
/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time, /* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
* while mem info is valid on remote CPU. * 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; 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); struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
/* Convert xdp_buff to xdp_frame */ /* 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))) if (unlikely((headroom - metasize) < sizeof(*xdp_frame)))
return NULL; 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 */ /* Store info in top of packet */
xdp_frame = xdp->data_hard_start; 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->len = xdp->data_end - xdp->data;
xdp_frame->headroom = headroom - sizeof(*xdp_frame); xdp_frame->headroom = headroom - sizeof(*xdp_frame);
xdp_frame->metasize = metasize; xdp_frame->metasize = metasize;
xdp_frame->frame_sz = xdp->frame_sz;
/* rxq only valid until napi_schedule ends, convert to xdp_mem_info */ /* rxq only valid until napi_schedule ends, convert to xdp_mem_info */
xdp_frame->mem = xdp->rxq->mem; xdp_frame->mem = xdp->rxq->mem;

8
net/core/xdp.c
View File

@ -11,6 +11,7 @@
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/idr.h> #include <linux/idr.h>
#include <linux/rhashtable.h> #include <linux/rhashtable.h>
#include <linux/bug.h>
#include <net/page_pool.h> #include <net/page_pool.h>
#include <net/xdp.h> #include <net/xdp.h>
@ -496,3 +497,10 @@ struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp)
return xdpf; return xdpf;
} }
EXPORT_SYMBOL_GPL(xdp_convert_zc_to_xdp_frame); 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);