| Message ID | 20221024172049.4187400-1-vladimir.oltean@nxp.com (mailing list archive) |
|---|---|
| State | Deferred |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] net: enetc: zeroize buffer descriptors in enetc_dma_alloc_bdr() | expand |
> -----Original Message----- > From: Vladimir Oltean <vladimir.oltean@nxp.com> > Sent: Monday, October 24, 2022 8:21 PM [...] > Subject: [PATCH net] net: enetc: zeroize buffer descriptors in > enetc_dma_alloc_bdr() > Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>
On Mon, Oct 24, 2022 at 08:20:49PM +0300, Vladimir Oltean wrote: > Under memory pressure, enetc_refill_rx_ring() may fail, and when called > during the enetc_open() -> enetc_setup_rxbdr() procedure, this is not > checked for. Please don't apply this yet, I'm still investigating a crash which has the symptoms described here, and I'm not sure why the patch didn't fix it.
On Wed, Oct 26, 2022 at 02:31:52AM +0300, Vladimir Oltean wrote: > On Mon, Oct 24, 2022 at 08:20:49PM +0300, Vladimir Oltean wrote: > > Under memory pressure, enetc_refill_rx_ring() may fail, and when called > > during the enetc_open() -> enetc_setup_rxbdr() procedure, this is not > > checked for. > > Please don't apply this yet, I'm still investigating a crash which has > the symptoms described here, and I'm not sure why the patch didn't fix it. Superseded by v2: https://patchwork.kernel.org/project/netdevbpf/patch/20221026121330.2042989-1-vladimir.oltean@nxp.com/
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c index 54bc92fc6bf0..1c272ca3a05a 100644 --- a/drivers/net/ethernet/freescale/enetc/enetc.c +++ b/drivers/net/ethernet/freescale/enetc/enetc.c @@ -1738,18 +1738,21 @@ void enetc_get_si_caps(struct enetc_si *si) static int enetc_dma_alloc_bdr(struct enetc_bdr *r, size_t bd_size) { - r->bd_base = dma_alloc_coherent(r->dev, r->bd_count * bd_size, - &r->bd_dma_base, GFP_KERNEL); + size_t size = r->bd_count * bd_size; + + r->bd_base = dma_alloc_coherent(r->dev, size, &r->bd_dma_base, + GFP_KERNEL); if (!r->bd_base) return -ENOMEM; /* h/w requires 128B alignment */ if (!IS_ALIGNED(r->bd_dma_base, 128)) { - dma_free_coherent(r->dev, r->bd_count * bd_size, r->bd_base, - r->bd_dma_base); + dma_free_coherent(r->dev, size, r->bd_base, r->bd_dma_base); return -EINVAL; } + memset(r->bd_base, 0, size); + return 0; }
Under memory pressure, enetc_refill_rx_ring() may fail, and when called during the enetc_open() -> enetc_setup_rxbdr() procedure, this is not checked for. An extreme case of memory pressure will result in exactly zero buffers being allocated for the RX ring, and in such a case it is expected that hardware drops all RX packets due to lack of buffers. The hardware drop happens, however the driver has undefined behavior and may even crash. Explanation follows below. The enetc NAPI poll procedure is shared between RX and TX conf, and enetc_poll() calls enetc_clean_rx_ring() even if the reason why NAPI was scheduled is TX. The enetc_clean_rx_ring() function (and its XDP derivative) is not prepared to handle such a condition. It has this loop exit condition: rxbd = enetc_rxbd(rx_ring, i); bd_status = le32_to_cpu(rxbd->r.lstatus); if (!bd_status) break; otherwise said, the NAPI poll procedure does not look at the Producer Index of the RX ring, instead it just walks circularly through the descriptors until it finds one which is not Ready. The problem is that the enetc_rxbd(rx_ring, i) RX descriptor is only initialized by enetc_refill_rx_ring() if page allocation has succeeded. So if memory allocation ever failed, enetc_clean_rx_ring() looks at rxbd->r.lstatus as an exit condition, but "rxbd" itself is uninitialized memory. If it contains junk, then junk buffers will be processed. To fix the problem, memset the DMA coherent area used for BD rings. This makes all BDs be "not ready" by default, which makes enetc_clean_rx_ring() exit early from the BD processing loop when there is no valid buffer available. Fixes: d4fd0404c1c9 ("enetc: Introduce basic PF and VF ENETC ethernet drivers") Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> --- drivers/net/ethernet/freescale/enetc/enetc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)