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Daniel Borkmann says:

====================
pull-request: bpf-next 2021-06-17

The following pull-request contains BPF updates for your *net-next* tree.

We've added 50 non-merge commits during the last 25 day(s) which contain
a total of 148 files changed, 4779 insertions(+), 1248 deletions(-).

The main changes are:

1) BPF infrastructure to migrate TCP child sockets from a listener to another
   in the same reuseport group/map, from Kuniyuki Iwashima.

2) Add a provably sound, faster and more precise algorithm for tnum_mul() as
   noted in https://arxiv.org/abs/2105.05398, from Harishankar Vishwanathan.

3) Streamline error reporting changes in libbpf as planned out in the
   'libbpf: the road to v1.0' effort, from Andrii Nakryiko.

4) Add broadcast support to xdp_redirect_map(), from Hangbin Liu.

5) Extends bpf_map_lookup_and_delete_elem() functionality to 4 more map
   types, that is, {LRU_,PERCPU_,LRU_PERCPU_,}HASH, from Denis Salopek.

6) Support new LLVM relocations in libbpf to make them more linker friendly,
   also add a doc to describe the BPF backend relocations, from Yonghong Song.

7) Silence long standing KUBSAN complaints on register-based shifts in
   interpreter, from Daniel Borkmann and Eric Biggers.

8) Add dummy PT_REGS macros in libbpf to fail BPF program compilation when
   target arch cannot be determined, from Lorenz Bauer.

9) Extend AF_XDP to support large umems with 1M+ pages, from Magnus Karlsson.

10) Fix two minor libbpf tc BPF API issues, from Kumar Kartikeya Dwivedi.

11) Move libbpf BPF_SEQ_PRINTF/BPF_SNPRINTF macros that can be used by BPF
    programs to bpf_helpers.h header, from Florent Revest.
====================

Signed-off-by: David S. Miller <[email protected]>
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davem330 committed Jun 17, 2021
2 parents 4de7725 + f20792d commit a52171a
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1 change: 1 addition & 0 deletions Documentation/bpf/index.rst
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Expand Up @@ -84,6 +84,7 @@ Other
:maxdepth: 1

ringbuf
llvm_reloc

.. Links:
.. _networking-filter: ../networking/filter.rst
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240 changes: 240 additions & 0 deletions Documentation/bpf/llvm_reloc.rst
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@@ -0,0 +1,240 @@
.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
====================
BPF LLVM Relocations
====================

This document describes LLVM BPF backend relocation types.

Relocation Record
=================

LLVM BPF backend records each relocation with the following 16-byte
ELF structure::

typedef struct
{
Elf64_Addr r_offset; // Offset from the beginning of section.
Elf64_Xword r_info; // Relocation type and symbol index.
} Elf64_Rel;

For example, for the following code::

int g1 __attribute__((section("sec")));
int g2 __attribute__((section("sec")));
static volatile int l1 __attribute__((section("sec")));
static volatile int l2 __attribute__((section("sec")));
int test() {
return g1 + g2 + l1 + l2;
}

Compiled with ``clang -target bpf -O2 -c test.c``, the following is
the code with ``llvm-objdump -dr test.o``::

0: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
0000000000000000: R_BPF_64_64 g1
2: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0)
3: 18 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r2 = 0 ll
0000000000000018: R_BPF_64_64 g2
5: 61 20 00 00 00 00 00 00 r0 = *(u32 *)(r2 + 0)
6: 0f 10 00 00 00 00 00 00 r0 += r1
7: 18 01 00 00 08 00 00 00 00 00 00 00 00 00 00 00 r1 = 8 ll
0000000000000038: R_BPF_64_64 sec
9: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0)
10: 0f 10 00 00 00 00 00 00 r0 += r1
11: 18 01 00 00 0c 00 00 00 00 00 00 00 00 00 00 00 r1 = 12 ll
0000000000000058: R_BPF_64_64 sec
13: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0)
14: 0f 10 00 00 00 00 00 00 r0 += r1
15: 95 00 00 00 00 00 00 00 exit

There are four relations in the above for four ``LD_imm64`` instructions.
The following ``llvm-readelf -r test.o`` shows the binary values of the four
relocations::

Relocation section '.rel.text' at offset 0x190 contains 4 entries:
Offset Info Type Symbol's Value Symbol's Name
0000000000000000 0000000600000001 R_BPF_64_64 0000000000000000 g1
0000000000000018 0000000700000001 R_BPF_64_64 0000000000000004 g2
0000000000000038 0000000400000001 R_BPF_64_64 0000000000000000 sec
0000000000000058 0000000400000001 R_BPF_64_64 0000000000000000 sec

Each relocation is represented by ``Offset`` (8 bytes) and ``Info`` (8 bytes).
For example, the first relocation corresponds to the first instruction
(Offset 0x0) and the corresponding ``Info`` indicates the relocation type
of ``R_BPF_64_64`` (type 1) and the entry in the symbol table (entry 6).
The following is the symbol table with ``llvm-readelf -s test.o``::

Symbol table '.symtab' contains 8 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS test.c
2: 0000000000000008 4 OBJECT LOCAL DEFAULT 4 l1
3: 000000000000000c 4 OBJECT LOCAL DEFAULT 4 l2
4: 0000000000000000 0 SECTION LOCAL DEFAULT 4 sec
5: 0000000000000000 128 FUNC GLOBAL DEFAULT 2 test
6: 0000000000000000 4 OBJECT GLOBAL DEFAULT 4 g1
7: 0000000000000004 4 OBJECT GLOBAL DEFAULT 4 g2

The 6th entry is global variable ``g1`` with value 0.

Similarly, the second relocation is at ``.text`` offset ``0x18``, instruction 3,
for global variable ``g2`` which has a symbol value 4, the offset
from the start of ``.data`` section.

The third and fourth relocations refers to static variables ``l1``
and ``l2``. From ``.rel.text`` section above, it is not clear
which symbols they really refers to as they both refers to
symbol table entry 4, symbol ``sec``, which has ``STT_SECTION`` type
and represents a section. So for static variable or function,
the section offset is written to the original insn
buffer, which is called ``A`` (addend). Looking at
above insn ``7`` and ``11``, they have section offset ``8`` and ``12``.
From symbol table, we can find that they correspond to entries ``2``
and ``3`` for ``l1`` and ``l2``.

In general, the ``A`` is 0 for global variables and functions,
and is the section offset or some computation result based on
section offset for static variables/functions. The non-section-offset
case refers to function calls. See below for more details.

Different Relocation Types
==========================

Six relocation types are supported. The following is an overview and
``S`` represents the value of the symbol in the symbol table::

Enum ELF Reloc Type Description BitSize Offset Calculation
0 R_BPF_NONE None
1 R_BPF_64_64 ld_imm64 insn 32 r_offset + 4 S + A
2 R_BPF_64_ABS64 normal data 64 r_offset S + A
3 R_BPF_64_ABS32 normal data 32 r_offset S + A
4 R_BPF_64_NODYLD32 .BTF[.ext] data 32 r_offset S + A
10 R_BPF_64_32 call insn 32 r_offset + 4 (S + A) / 8 - 1

For example, ``R_BPF_64_64`` relocation type is used for ``ld_imm64`` instruction.
The actual to-be-relocated data (0 or section offset)
is stored at ``r_offset + 4`` and the read/write
data bitsize is 32 (4 bytes). The relocation can be resolved with
the symbol value plus implicit addend. Note that the ``BitSize`` is 32 which
means the section offset must be less than or equal to ``UINT32_MAX`` and this
is enforced by LLVM BPF backend.

In another case, ``R_BPF_64_ABS64`` relocation type is used for normal 64-bit data.
The actual to-be-relocated data is stored at ``r_offset`` and the read/write data
bitsize is 64 (8 bytes). The relocation can be resolved with
the symbol value plus implicit addend.

Both ``R_BPF_64_ABS32`` and ``R_BPF_64_NODYLD32`` types are for 32-bit data.
But ``R_BPF_64_NODYLD32`` specifically refers to relocations in ``.BTF`` and
``.BTF.ext`` sections. For cases like bcc where llvm ``ExecutionEngine RuntimeDyld``
is involved, ``R_BPF_64_NODYLD32`` types of relocations should not be resolved
to actual function/variable address. Otherwise, ``.BTF`` and ``.BTF.ext``
become unusable by bcc and kernel.

Type ``R_BPF_64_32`` is used for call instruction. The call target section
offset is stored at ``r_offset + 4`` (32bit) and calculated as
``(S + A) / 8 - 1``.

Examples
========

Types ``R_BPF_64_64`` and ``R_BPF_64_32`` are used to resolve ``ld_imm64``
and ``call`` instructions. For example::

__attribute__((noinline)) __attribute__((section("sec1")))
int gfunc(int a, int b) {
return a * b;
}
static __attribute__((noinline)) __attribute__((section("sec1")))
int lfunc(int a, int b) {
return a + b;
}
int global __attribute__((section("sec2")));
int test(int a, int b) {
return gfunc(a, b) + lfunc(a, b) + global;
}

Compiled with ``clang -target bpf -O2 -c test.c``, we will have
following code with `llvm-objdump -dr test.o``::

Disassembly of section .text:

0000000000000000 <test>:
0: bf 26 00 00 00 00 00 00 r6 = r2
1: bf 17 00 00 00 00 00 00 r7 = r1
2: 85 10 00 00 ff ff ff ff call -1
0000000000000010: R_BPF_64_32 gfunc
3: bf 08 00 00 00 00 00 00 r8 = r0
4: bf 71 00 00 00 00 00 00 r1 = r7
5: bf 62 00 00 00 00 00 00 r2 = r6
6: 85 10 00 00 02 00 00 00 call 2
0000000000000030: R_BPF_64_32 sec1
7: 0f 80 00 00 00 00 00 00 r0 += r8
8: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
0000000000000040: R_BPF_64_64 global
10: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0)
11: 0f 10 00 00 00 00 00 00 r0 += r1
12: 95 00 00 00 00 00 00 00 exit

Disassembly of section sec1:

0000000000000000 <gfunc>:
0: bf 20 00 00 00 00 00 00 r0 = r2
1: 2f 10 00 00 00 00 00 00 r0 *= r1
2: 95 00 00 00 00 00 00 00 exit

0000000000000018 <lfunc>:
3: bf 20 00 00 00 00 00 00 r0 = r2
4: 0f 10 00 00 00 00 00 00 r0 += r1
5: 95 00 00 00 00 00 00 00 exit

The first relocation corresponds to ``gfunc(a, b)`` where ``gfunc`` has a value of 0,
so the ``call`` instruction offset is ``(0 + 0)/8 - 1 = -1``.
The second relocation corresponds to ``lfunc(a, b)`` where ``lfunc`` has a section
offset ``0x18``, so the ``call`` instruction offset is ``(0 + 0x18)/8 - 1 = 2``.
The third relocation corresponds to ld_imm64 of ``global``, which has a section
offset ``0``.

The following is an example to show how R_BPF_64_ABS64 could be generated::

int global() { return 0; }
struct t { void *g; } gbl = { global };

Compiled with ``clang -target bpf -O2 -g -c test.c``, we will see a
relocation below in ``.data`` section with command
``llvm-readelf -r test.o``::

Relocation section '.rel.data' at offset 0x458 contains 1 entries:
Offset Info Type Symbol's Value Symbol's Name
0000000000000000 0000000700000002 R_BPF_64_ABS64 0000000000000000 global

The relocation says the first 8-byte of ``.data`` section should be
filled with address of ``global`` variable.

With ``llvm-readelf`` output, we can see that dwarf sections have a bunch of
``R_BPF_64_ABS32`` and ``R_BPF_64_ABS64`` relocations::

Relocation section '.rel.debug_info' at offset 0x468 contains 13 entries:
Offset Info Type Symbol's Value Symbol's Name
0000000000000006 0000000300000003 R_BPF_64_ABS32 0000000000000000 .debug_abbrev
000000000000000c 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str
0000000000000012 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str
0000000000000016 0000000600000003 R_BPF_64_ABS32 0000000000000000 .debug_line
000000000000001a 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str
000000000000001e 0000000200000002 R_BPF_64_ABS64 0000000000000000 .text
000000000000002b 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str
0000000000000037 0000000800000002 R_BPF_64_ABS64 0000000000000000 gbl
0000000000000040 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str
......

The .BTF/.BTF.ext sections has R_BPF_64_NODYLD32 relocations::

Relocation section '.rel.BTF' at offset 0x538 contains 1 entries:
Offset Info Type Symbol's Value Symbol's Name
0000000000000084 0000000800000004 R_BPF_64_NODYLD32 0000000000000000 gbl

Relocation section '.rel.BTF.ext' at offset 0x548 contains 2 entries:
Offset Info Type Symbol's Value Symbol's Name
000000000000002c 0000000200000004 R_BPF_64_NODYLD32 0000000000000000 .text
0000000000000040 0000000200000004 R_BPF_64_NODYLD32 0000000000000000 .text
25 changes: 25 additions & 0 deletions Documentation/networking/ip-sysctl.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -761,6 +761,31 @@ tcp_syncookies - INTEGER
network connections you can set this knob to 2 to enable
unconditionally generation of syncookies.

tcp_migrate_req - BOOLEAN
The incoming connection is tied to a specific listening socket when
the initial SYN packet is received during the three-way handshake.
When a listener is closed, in-flight request sockets during the
handshake and established sockets in the accept queue are aborted.

If the listener has SO_REUSEPORT enabled, other listeners on the
same port should have been able to accept such connections. This
option makes it possible to migrate such child sockets to another
listener after close() or shutdown().

The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should
usually be used to define the policy to pick an alive listener.
Otherwise, the kernel will randomly pick an alive listener only if
this option is enabled.

Note that migration between listeners with different settings may
crash applications. Let's say migration happens from listener A to
B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from
the requests migrated from A. To avoid such a situation, cancel
migration by returning SK_DROP in the type of eBPF program, or
disable this option.

Default: 0

tcp_fastopen - INTEGER
Enable TCP Fast Open (RFC7413) to send and accept data in the opening
SYN packet.
Expand Down
23 changes: 23 additions & 0 deletions include/linux/bpf.h
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Expand Up @@ -70,6 +70,8 @@ struct bpf_map_ops {
void *(*map_lookup_elem_sys_only)(struct bpf_map *map, void *key);
int (*map_lookup_batch)(struct bpf_map *map, const union bpf_attr *attr,
union bpf_attr __user *uattr);
int (*map_lookup_and_delete_elem)(struct bpf_map *map, void *key,
void *value, u64 flags);
int (*map_lookup_and_delete_batch)(struct bpf_map *map,
const union bpf_attr *attr,
union bpf_attr __user *uattr);
Expand Down Expand Up @@ -1499,8 +1501,13 @@ int dev_xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
struct net_device *dev_rx);
int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
struct net_device *dev_rx);
int dev_map_enqueue_multi(struct xdp_buff *xdp, struct net_device *dev_rx,
struct bpf_map *map, bool exclude_ingress);
int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
struct bpf_prog *xdp_prog);
int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
struct bpf_prog *xdp_prog, struct bpf_map *map,
bool exclude_ingress);
bool dev_map_can_have_prog(struct bpf_map *map);

void __cpu_map_flush(void);
Expand Down Expand Up @@ -1668,6 +1675,13 @@ int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
return 0;
}

static inline
int dev_map_enqueue_multi(struct xdp_buff *xdp, struct net_device *dev_rx,
struct bpf_map *map, bool exclude_ingress)
{
return 0;
}

struct sk_buff;

static inline int dev_map_generic_redirect(struct bpf_dtab_netdev *dst,
Expand All @@ -1677,6 +1691,14 @@ static inline int dev_map_generic_redirect(struct bpf_dtab_netdev *dst,
return 0;
}

static inline
int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
struct bpf_prog *xdp_prog, struct bpf_map *map,
bool exclude_ingress)
{
return 0;
}

static inline void __cpu_map_flush(void)
{
}
Expand Down Expand Up @@ -2026,6 +2048,7 @@ struct sk_reuseport_kern {
struct sk_buff *skb;
struct sock *sk;
struct sock *selected_sk;
struct sock *migrating_sk;
void *data_end;
u32 hash;
u32 reuseport_id;
Expand Down
4 changes: 2 additions & 2 deletions include/linux/bpf_local_storage.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ struct bpf_local_storage_data {
* from the object's bpf_local_storage.
*
* Put it in the same cacheline as the data to minimize
* the number of cachelines access during the cache hit case.
* the number of cachelines accessed during the cache hit case.
*/
struct bpf_local_storage_map __rcu *smap;
u8 data[] __aligned(8);
Expand All @@ -71,7 +71,7 @@ struct bpf_local_storage_elem {
struct bpf_local_storage __rcu *local_storage;
struct rcu_head rcu;
/* 8 bytes hole */
/* The data is stored in aother cacheline to minimize
/* The data is stored in another cacheline to minimize
* the number of cachelines access during a cache hit.
*/
struct bpf_local_storage_data sdata ____cacheline_aligned;
Expand Down
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