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Date: Fri, 3 Aug 2018 11:49:02 -0700
From: Doron Roberts-Kedes <doronrk@...com>
To: Vakul Garg <vakul.garg@....com>
CC: "David S . Miller" <davem@...emloft.net>,
Dave Watson <davejwatson@...com>,
Boris Pismenny <borisp@...lanox.com>,
Aviad Yehezkel <aviadye@...lanox.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net/tls: Calculate nsg for zerocopy path
without skb_cow_data.
On Fri, Aug 03, 2018 at 01:23:33AM +0000, Vakul Garg wrote:
>
>
> > -----Original Message-----
> > From: Doron Roberts-Kedes [mailto:doronrk@...com]
> > Sent: Friday, August 3, 2018 6:00 AM
> > To: David S . Miller <davem@...emloft.net>
> > Cc: Dave Watson <davejwatson@...com>; Vakul Garg
> > <vakul.garg@....com>; Boris Pismenny <borisp@...lanox.com>; Aviad
> > Yehezkel <aviadye@...lanox.com>; netdev@...r.kernel.org; Doron
> > Roberts-Kedes <doronrk@...com>
> > Subject: [PATCH net-next] net/tls: Calculate nsg for zerocopy path without
> > skb_cow_data.
> >
> > decrypt_skb fails if the number of sg elements required to map is greater
> > than MAX_SKB_FRAGS. As noted by Vakul Garg, nsg must always be
> > calculated, but skb_cow_data adds unnecessary memcpy's for the zerocopy
> > case.
> >
> > The new function skb_nsg calculates the number of scatterlist elements
> > required to map the skb without the extra overhead of skb_cow_data. This
> > function mimics the structure of skb_to_sgvec.
> >
> > Fixes: c46234ebb4d1 ("tls: RX path for ktls")
> > Signed-off-by: Doron Roberts-Kedes <doronrk@...com>
> > ---
> > net/tls/tls_sw.c | 89
> > ++++++++++++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 86 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c index
> > ff3a6904a722..c62793601cfc 100644
> > --- a/net/tls/tls_sw.c
> > +++ b/net/tls/tls_sw.c
> > @@ -43,6 +43,76 @@
> >
> > #define MAX_IV_SIZE TLS_CIPHER_AES_GCM_128_IV_SIZE
> >
> > +static int __skb_nsg(struct sk_buff *skb, int offset, int len,
> > + unsigned int recursion_level)
> > +{
> > + int start = skb_headlen(skb);
> > + int i, copy = start - offset;
> > + struct sk_buff *frag_iter;
> > + int elt = 0;
> > +
> > + if (unlikely(recursion_level >= 24))
> > + return -EMSGSIZE;
> > +
> > + if (copy > 0) {
> > + if (copy > len)
> > + copy = len;
> > + elt++;
> > + if ((len -= copy) == 0)
> > + return elt;
> > + offset += copy;
> > + }
> > +
> > + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> > + int end;
> > +
> > + WARN_ON(start > offset + len);
> > +
> > + end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
> > + if ((copy = end - offset) > 0) {
> > + if (copy > len)
> > + copy = len;
> > + elt++;
> > + if (!(len -= copy))
> > + return elt;
> > + offset += copy;
> > + }
> > + start = end;
> > + }
> > +
> > + skb_walk_frags(skb, frag_iter) {
> > + int end, ret;
> > +
> > + WARN_ON(start > offset + len);
> > +
> > + end = start + frag_iter->len;
> > + if ((copy = end - offset) > 0) {
> > +
> > + if (copy > len)
> > + copy = len;
> > + ret = __skb_nsg(frag_iter, offset - start, copy,
> > + recursion_level + 1);
> > + if (unlikely(ret < 0))
> > + return ret;
> > + elt += ret;
> > + if ((len -= copy) == 0)
> > + return elt;
> > + offset += copy;
> > + }
> > + start = end;
> > + }
> > + BUG_ON(len);
> > + return elt;
> > +}
> > +
> > +/* Return the number of scatterlist elements required to completely map
> > +the
> > + * skb, or -EMSGSIZE if the recursion depth is exceeded.
> > + */
> > +static int skb_nsg(struct sk_buff *skb, int offset, int len) {
> > + return __skb_nsg(skb, offset, len, 0); }
> > +
>
> These is generic function and useful elsewhere too.
> Should the above two functions be exported by skbuff.c?
True. Perhaps it can move into skbuff.c if/when there is a second
use case for it.
>
> > static int tls_do_decryption(struct sock *sk,
> > struct scatterlist *sgin,
> > struct scatterlist *sgout,
> > @@ -693,7 +763,7 @@ int decrypt_skb(struct sock *sk, struct sk_buff *skb,
> > struct scatterlist sgin_arr[MAX_SKB_FRAGS + 2];
> > struct scatterlist *sgin = &sgin_arr[0];
> > struct strp_msg *rxm = strp_msg(skb);
> > - int ret, nsg = ARRAY_SIZE(sgin_arr);
> > + int ret, nsg;
> > struct sk_buff *unused;
> >
> > ret = skb_copy_bits(skb, rxm->offset + TLS_HEADER_SIZE, @@ -
> > 704,10 +774,23 @@ int decrypt_skb(struct sock *sk, struct sk_buff *skb,
> >
> > memcpy(iv, tls_ctx->rx.iv, TLS_CIPHER_AES_GCM_128_SALT_SIZE);
> > if (!sgout) {
> > - nsg = skb_cow_data(skb, 0, &unused) + 1;
> > + nsg = skb_cow_data(skb, 0, &unused);
> > + } else {
> > + nsg = skb_nsg(skb,
> > + rxm->offset + tls_ctx->rx.prepend_size,
> > + rxm->full_len - tls_ctx->rx.prepend_size);
> > + if (nsg <= 0)
> > + return nsg;
> Comparison should be (nsg < 1). TLS forbids '0' sized records.
Yes true, v2 incoming
>
> > + }
> > +
> > + // We need one extra for ctx->rx_aad_ciphertext
> > + nsg++;
> > +
> > + if (nsg > ARRAY_SIZE(sgin_arr))
> > sgin = kmalloc_array(nsg, sizeof(*sgin), sk->sk_allocation);
>
> Add check for kmalloc_array returnining NULL.
Yes true, v2 incoming.
>
> > +
> > + if (!sgout)
> > sgout = sgin;
> > - }
> >
> > sg_init_table(sgin, nsg);
> > sg_set_buf(&sgin[0], ctx->rx_aad_ciphertext, TLS_AAD_SPACE_SIZE);
> > --
> > 2.17.1
>
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