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bpf: Keep the (rcv) timestamp behavior for the existing tc-bpf@ingress 

The current tc-bpf@ingress reads and writes the __sk_buff->tstamp
as a (rcv) timestamp which currently could either be 0 (not available)
or ktime_get_real().  This patch is to backward compatible with the
(rcv) timestamp expectation at ingress.  If the skb->tstamp has
the delivery_time, the bpf insn rewrite will read 0 for tc-bpf
running at ingress as it is not available.  When writing at ingress,
it will also clear the skb->mono_delivery_time bit.

/* BPF_READ: a = __sk_buff->tstamp */
if (!skb->tc_at_ingress || !skb->mono_delivery_time)
	a = skb->tstamp;
else
	a = 0

/* BPF_WRITE: __sk_buff->tstamp = a */
if (skb->tc_at_ingress)
	skb->mono_delivery_time = 0;
skb->tstamp = a;

[ A note on the BPF_CGROUP_INET_INGRESS which can also access
  skb->tstamp.  At that point, the skb is delivered locally
  and skb_clear_delivery_time() has already been done,
  so the skb->tstamp will only have the (rcv) timestamp. ]

If the tc-bpf@egress writes 0 to skb->tstamp, the skb->mono_delivery_time
has to be cleared also.  It could be done together during
convert_ctx_access().  However, the latter patch will also expose
the skb->mono_delivery_time bit as __sk_buff->delivery_time_type.
Changing the delivery_time_type in the background may surprise
the user, e.g. the 2nd read on __sk_buff->delivery_time_type
may need a READ_ONCE() to avoid compiler optimization.  Thus,
in expecting the needs in the latter patch, this patch does a
check on !skb->tstamp after running the tc-bpf and clears the
skb->mono_delivery_time bit if needed.  The earlier discussion
on v4 [0].

The bpf insn rewrite requires the skb's mono_delivery_time bit and
tc_at_ingress bit.  They are moved up in sk_buff so that bpf rewrite
can be done at a fixed offset.  tc_skip_classify is moved together with
tc_at_ingress.  To get one bit for mono_delivery_time, csum_not_inet is
moved down and this bit is currently used by sctp.

[0]: https://lore.kernel.org/bpf/20220217015043.khqwqklx45c4m4se@kafai-mbp.dhcp.thefacebook.com/

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Martin KaFai Lau 2022-03-02 11:56:28 -08:00 committed by David S. Miller
parent cd14e9b7b8
commit 7449197d60
4 changed files with 77 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
include/linux/skbuff.h
View File

@ -941,8 +941,12 @@ struct sk_buff {
__u8 vlan_present:1; /* See PKT_VLAN_PRESENT_BIT */
__u8 csum_complete_sw:1;
__u8 csum_level:2;
__u8 csum_not_inet:1;
__u8 dst_pending_confirm:1;
__u8 mono_delivery_time:1;
#ifdef CONFIG_NET_CLS_ACT
__u8 tc_skip_classify:1;
__u8 tc_at_ingress:1;
#endif
#ifdef CONFIG_IPV6_NDISC_NODETYPE
__u8 ndisc_nodetype:2;
#endif
@ -953,10 +957,6 @@ struct sk_buff {
#ifdef CONFIG_NET_SWITCHDEV
__u8 offload_fwd_mark:1;
__u8 offload_l3_fwd_mark:1;
#endif
#ifdef CONFIG_NET_CLS_ACT
__u8 tc_skip_classify:1;
__u8 tc_at_ingress:1;
#endif
__u8 redirected:1;
#ifdef CONFIG_NET_REDIRECT
@ -969,7 +969,7 @@ struct sk_buff {
__u8 decrypted:1;
#endif
__u8 slow_gro:1;
__u8 mono_delivery_time:1;
__u8 csum_not_inet:1;
#ifdef CONFIG_NET_SCHED
__u16 tc_index; /* traffic control index */
@ -1047,10 +1047,16 @@ struct sk_buff {
/* if you move pkt_vlan_present around you also must adapt these constants */
#ifdef __BIG_ENDIAN_BITFIELD
#define PKT_VLAN_PRESENT_BIT 7
#define TC_AT_INGRESS_MASK (1 << 0)
#define SKB_MONO_DELIVERY_TIME_MASK (1 << 2)
#else
#define PKT_VLAN_PRESENT_BIT 0
#define TC_AT_INGRESS_MASK (1 << 7)
#define SKB_MONO_DELIVERY_TIME_MASK (1 << 5)
#endif
#define PKT_VLAN_PRESENT_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
#define TC_AT_INGRESS_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
#define SKB_MONO_DELIVERY_TIME_OFFSET offsetof(struct sk_buff, __pkt_vlan_present_offset)
#ifdef __KERNEL__
/*

71
net/core/filter.c
View File

@ -8859,6 +8859,65 @@ static struct bpf_insn *bpf_convert_shinfo_access(const struct bpf_insn *si,
return insn;
}
static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->dst_reg;
__u8 skb_reg = si->src_reg;
#ifdef CONFIG_NET_CLS_ACT
__u8 tmp_reg = BPF_REG_AX;
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 5);
/* @ingress, read __sk_buff->tstamp as the (rcv) timestamp,
* so check the skb->mono_delivery_time.
*/
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
SKB_MONO_DELIVERY_TIME_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
SKB_MONO_DELIVERY_TIME_MASK);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 2);
/* skb->mono_delivery_time is set, read 0 as the (rcv) timestamp. */
*insn++ = BPF_MOV64_IMM(value_reg, 0);
*insn++ = BPF_JMP_A(1);
#endif
*insn++ = BPF_LDX_MEM(BPF_DW, value_reg, skb_reg,
offsetof(struct sk_buff, tstamp));
return insn;
}
static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_insn *si,
struct bpf_insn *insn)
{
__u8 value_reg = si->src_reg;
__u8 skb_reg = si->dst_reg;
#ifdef CONFIG_NET_CLS_ACT
__u8 tmp_reg = BPF_REG_AX;
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, TC_AT_INGRESS_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK);
*insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg, 0, 3);
/* Writing __sk_buff->tstamp at ingress as the (rcv) timestamp.
* Clear the skb->mono_delivery_time.
*/
*insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
SKB_MONO_DELIVERY_TIME_OFFSET);
*insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
~SKB_MONO_DELIVERY_TIME_MASK);
*insn++ = BPF_STX_MEM(BPF_B, skb_reg, tmp_reg,
SKB_MONO_DELIVERY_TIME_OFFSET);
#endif
/* skb->tstamp = tstamp */
*insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg,
offsetof(struct sk_buff, tstamp));
return insn;
}
static u32 bpf_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
@ -9167,17 +9226,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
BUILD_BUG_ON(sizeof_field(struct sk_buff, tstamp) != 8);
if (type == BPF_WRITE)
*insn++ = BPF_STX_MEM(BPF_DW,
si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff,
tstamp, 8,
target_size));
insn = bpf_convert_tstamp_write(si, insn);
else
*insn++ = BPF_LDX_MEM(BPF_DW,
si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff,
tstamp, 8,
target_size));
insn = bpf_convert_tstamp_read(si, insn);
break;
case offsetof(struct __sk_buff, gso_segs):

2
net/sched/act_bpf.c
View File

@ -53,6 +53,8 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act,
bpf_compute_data_pointers(skb);
filter_res = bpf_prog_run(filter, skb);
}
if (unlikely(!skb->tstamp && skb->mono_delivery_time))
skb->mono_delivery_time = 0;
if (skb_sk_is_prefetched(skb) && filter_res != TC_ACT_OK)
skb_orphan(skb);

2
net/sched/cls_bpf.c
View File

@ -102,6 +102,8 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
bpf_compute_data_pointers(skb);
filter_res = bpf_prog_run(prog->filter, skb);
}
if (unlikely(!skb->tstamp && skb->mono_delivery_time))
skb->mono_delivery_time = 0;
if (prog->exts_integrated) {
res->class = 0;