linux-stable.git/kernel/bpf/btf.c, branch v5.6

bpf: Explicitly memset some bpf info structures declared on the stack

2020-03-20T20:05:22+00:00

Trying to initialize a structure with "= {};" will not always clean out
all padding locations in a structure. So be explicit and call memset to
initialize everything for a number of bpf information structures that
are then copied from userspace, sometimes from smaller memory locations
than the size of the structure.

Reported-by: Daniel Borkmann 
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Daniel Borkmann 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20200320162258.GA794295@kroah.com

bpf/btf: Fix BTF verification of enum members in struct/union

2020-03-10T17:00:41+00:00

btf_enum_check_member() was currently sure to recognize the size of
"enum" type members in struct/union as the size of "int" even if
its size was packed.

This patch fixes BTF enum verification to use the correct size
of member in BPF programs.

Fixes: 179cde8cef7e ("bpf: btf: Check members of struct/union")
Signed-off-by: Yoshiki Komachi 
Signed-off-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/1583825550-18606-2-git-send-email-komachi.yoshiki@gmail.com

bpf: Make btf_check_func_type_match() static

2020-02-10T23:22:47+00:00

Fix the following sparse warning:

kernel/bpf/btf.c:4131:5: warning: symbol 'btf_check_func_type_match' was
not declared. Should it be static?

Reported-by: Hulk Robot 
Signed-off-by: Hongbo Yao 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20200210011441.147102-1-yaohongbo@huawei.com

bpf: Fix modifier skipping logic

2020-02-03T23:06:07+00:00

Fix the way modifiers are skipped while walking pointers. Otherwise second
level dereferences of 'const struct foo *' will be rejected by the verifier.

Fixes: 9e15db66136a ("bpf: Implement accurate raw_tp context access via BTF")
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Daniel Borkmann 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20200201000314.261392-1-ast@kernel.org

bpf: Reuse log from btf_prase_vmlinux() in btf_struct_ops_init()

2020-01-29T15:40:54+00:00

Instead of using a locally defined "struct bpf_verifier_log log = {}",
btf_struct_ops_init() should reuse the "log" from its calling
function "btf_parse_vmlinux()".  It should also resolve the
frame-size too large compiler warning in some ARCH.

Fixes: 27ae7997a661 ("bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS")
Signed-off-by: Martin KaFai Lau 
Signed-off-by: Daniel Borkmann 
Acked-by: Andrii Nakryiko 
Acked-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/20200127175145.1154438-1-kafai@fb.com

bpf: Allow BTF ctx access for string pointers

2020-01-25T15:12:40+00:00

When accessing the context we allow access to arguments with
scalar type and pointer to struct. But we deny access for
pointer to scalar type, which is the case for many functions.

Alexei suggested to take conservative approach and allow
currently only string pointer access, which is the case
for most functions now:

Adding check if the pointer is to string type and allow access to it.

Suggested-by: Alexei Starovoitov 
Signed-off-by: Jiri Olsa 
Signed-off-by: Alexei Starovoitov 
Link: https://lore.kernel.org/bpf/20200123161508.915203-2-jolsa@kernel.org

bpf: Introduce dynamic program extensions

2020-01-22T22:04:52+00:00

Introduce dynamic program extensions. The users can load additional BPF
functions and replace global functions in previously loaded BPF programs while
these programs are executing.

Global functions are verified individually by the verifier based on their types only.
Hence the global function in the new program which types match older function can
safely replace that corresponding function.

This new function/program is called 'an extension' of old program. At load time
the verifier uses (attach_prog_fd, attach_btf_id) pair to identify the function
to be replaced. The BPF program type is derived from the target program into
extension program. Technically bpf_verifier_ops is copied from target program.
The BPF_PROG_TYPE_EXT program type is a placeholder. It has empty verifier_ops.
The extension program can call the same bpf helper functions as target program.
Single BPF_PROG_TYPE_EXT type is used to extend XDP, SKB and all other program
types. The verifier allows only one level of replacement. Meaning that the
extension program cannot recursively extend an extension. That also means that
the maximum stack size is increasing from 512 to 1024 bytes and maximum
function nesting level from 8 to 16. The programs don't always consume that
much. The stack usage is determined by the number of on-stack variables used by
the program. The verifier could have enforced 512 limit for combined original
plus extension program, but it makes for difficult user experience. The main
use case for extensions is to provide generic mechanism to plug external
programs into policy program or function call chaining.

BPF trampoline is used to track both fentry/fexit and program extensions
because both are using the same nop slot at the beginning of every BPF
function. Attaching fentry/fexit to a function that was replaced is not
allowed. The opposite is true as well. Replacing a function that currently
being analyzed with fentry/fexit is not allowed. The executable page allocated
by BPF trampoline is not used by program extensions. This inefficiency will be
optimized in future patches.

Function by function verification of global function supports scalars and
pointer to context only. Hence program extensions are supported for such class
of global functions only. In the future the verifier will be extended with
support to pointers to structures, arrays with sizes, etc.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Acked-by: Andrii Nakryiko 
Acked-by: Toke Høiland-Jørgensen 
Link: https://lore.kernel.org/bpf/20200121005348.2769920-2-ast@kernel.org

bpf: Introduce function-by-function verification

2020-01-10T16:20:07+00:00

New llvm and old llvm with libbpf help produce BTF that distinguish global and
static functions. Unlike arguments of static function the arguments of global
functions cannot be removed or optimized away by llvm. The compiler has to use
exactly the arguments specified in a function prototype. The argument type
information allows the verifier validate each global function independently.
For now only supported argument types are pointer to context and scalars. In
the future pointers to structures, sizes, pointer to packet data can be
supported as well. Consider the following example:

static int f1(int ...)
{
  ...
}

int f3(int b);

int f2(int a)
{
  f1(a) + f3(a);
}

int f3(int b)
{
  ...
}

int main(...)
{
  f1(...) + f2(...) + f3(...);
}

The verifier will start its safety checks from the first global function f2().
It will recursively descend into f1() because it's static. Then it will check
that arguments match for the f3() invocation inside f2(). It will not descend
into f3(). It will finish f2() that has to be successfully verified for all
possible values of 'a'. Then it will proceed with f3(). That function also has
to be safe for all possible values of 'b'. Then it will start subprog 0 (which
is main() function). It will recursively descend into f1() and will skip full
check of f2() and f3(), since they are global. The order of processing global
functions doesn't affect safety, since all global functions must be proven safe
based on their arguments only.

Such function by function verification can drastically improve speed of the
verification and reduce complexity.

Note that the stack limit of 512 still applies to the call chain regardless whether
functions were static or global. The nested level of 8 also still applies. The
same recursion prevention checks are in place as well.

The type information and static/global kind is preserved after the verification
hence in the above example global function f2() and f3() can be replaced later
by equivalent functions with the same types that are loaded and verified later
without affecting safety of this main() program. Such replacement (re-linking)
of global functions is a subject of future patches.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: Daniel Borkmann 
Acked-by: Song Liu 
Link: https://lore.kernel.org/bpf/20200110064124.1760511-3-ast@kernel.org

bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS

2020-01-09T16:46:18+00:00

The patch introduces BPF_MAP_TYPE_STRUCT_OPS.  The map value
is a kernel struct with its func ptr implemented in bpf prog.
This new map is the interface to register/unregister/introspect
a bpf implemented kernel struct.

The kernel struct is actually embedded inside another new struct
(or called the "value" struct in the code).  For example,
"struct tcp_congestion_ops" is embbeded in:
struct bpf_struct_ops_tcp_congestion_ops {
	refcount_t refcnt;
	enum bpf_struct_ops_state state;
	struct tcp_congestion_ops data;  /* <-- kernel subsystem struct here */
}
The map value is "struct bpf_struct_ops_tcp_congestion_ops".
The "bpftool map dump" will then be able to show the
state ("inuse"/"tobefree") and the number of subsystem's refcnt (e.g.
number of tcp_sock in the tcp_congestion_ops case).  This "value" struct
is created automatically by a macro.  Having a separate "value" struct
will also make extending "struct bpf_struct_ops_XYZ" easier (e.g. adding
"void (*init)(void)" to "struct bpf_struct_ops_XYZ" to do some
initialization works before registering the struct_ops to the kernel
subsystem).  The libbpf will take care of finding and populating the
"struct bpf_struct_ops_XYZ" from "struct XYZ".

Register a struct_ops to a kernel subsystem:
1. Load all needed BPF_PROG_TYPE_STRUCT_OPS prog(s)
2. Create a BPF_MAP_TYPE_STRUCT_OPS with attr->btf_vmlinux_value_type_id
   set to the btf id "struct bpf_struct_ops_tcp_congestion_ops" of the
   running kernel.
   Instead of reusing the attr->btf_value_type_id,
   btf_vmlinux_value_type_id s added such that attr->btf_fd can still be
   used as the "user" btf which could store other useful sysadmin/debug
   info that may be introduced in the furture,
   e.g. creation-date/compiler-details/map-creator...etc.
3. Create a "struct bpf_struct_ops_tcp_congestion_ops" object as described
   in the running kernel btf.  Populate the value of this object.
   The function ptr should be populated with the prog fds.
4. Call BPF_MAP_UPDATE with the object created in (3) as
   the map value.  The key is always "0".

During BPF_MAP_UPDATE, the code that saves the kernel-func-ptr's
args as an array of u64 is generated.  BPF_MAP_UPDATE also allows
the specific struct_ops to do some final checks in "st_ops->init_member()"
(e.g. ensure all mandatory func ptrs are implemented).
If everything looks good, it will register this kernel struct
to the kernel subsystem.  The map will not allow further update
from this point.

Unregister a struct_ops from the kernel subsystem:
BPF_MAP_DELETE with key "0".

Introspect a struct_ops:
BPF_MAP_LOOKUP_ELEM with key "0".  The map value returned will
have the prog _id_ populated as the func ptr.

The map value state (enum bpf_struct_ops_state) will transit from:
INIT (map created) =>
INUSE (map updated, i.e. reg) =>
TOBEFREE (map value deleted, i.e. unreg)

The kernel subsystem needs to call bpf_struct_ops_get() and
bpf_struct_ops_put() to manage the "refcnt" in the
"struct bpf_struct_ops_XYZ".  This patch uses a separate refcnt
for the purose of tracking the subsystem usage.  Another approach
is to reuse the map->refcnt and then "show" (i.e. during map_lookup)
the subsystem's usage by doing map->refcnt - map->usercnt to filter out
the map-fd/pinned-map usage.  However, that will also tie down the
future semantics of map->refcnt and map->usercnt.

The very first subsystem's refcnt (during reg()) holds one
count to map->refcnt.  When the very last subsystem's refcnt
is gone, it will also release the map->refcnt.  All bpf_prog will be
freed when the map->refcnt reaches 0 (i.e. during map_free()).

Here is how the bpftool map command will look like:
[root@arch-fb-vm1 bpf]# bpftool map show
6: struct_ops  name dctcp  flags 0x0
	key 4B  value 256B  max_entries 1  memlock 4096B
	btf_id 6
[root@arch-fb-vm1 bpf]# bpftool map dump id 6
[{
        "value": {
            "refcnt": {
                "refs": {
                    "counter": 1
                }
            },
            "state": 1,
            "data": {
                "list": {
                    "next": 0,
                    "prev": 0
                },
                "key": 0,
                "flags": 2,
                "init": 24,
                "release": 0,
                "ssthresh": 25,
                "cong_avoid": 30,
                "set_state": 27,
                "cwnd_event": 28,
                "in_ack_event": 26,
                "undo_cwnd": 29,
                "pkts_acked": 0,
                "min_tso_segs": 0,
                "sndbuf_expand": 0,
                "cong_control": 0,
                "get_info": 0,
                "name": [98,112,102,95,100,99,116,99,112,0,0,0,0,0,0,0
                ],
                "owner": 0
            }
        }
    }
]

Misc Notes:
* bpf_struct_ops_map_sys_lookup_elem() is added for syscall lookup.
  It does an inplace update on "*value" instead returning a pointer
  to syscall.c.  Otherwise, it needs a separate copy of "zero" value
  for the BPF_STRUCT_OPS_STATE_INIT to avoid races.

* The bpf_struct_ops_map_delete_elem() is also called without
  preempt_disable() from map_delete_elem().  It is because
  the "->unreg()" may requires sleepable context, e.g.
  the "tcp_unregister_congestion_control()".

* "const" is added to some of the existing "struct btf_func_model *"
  function arg to avoid a compiler warning caused by this patch.

Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov 
Acked-by: Andrii Nakryiko 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20200109003505.3855919-1-kafai@fb.com

bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS

2020-01-09T16:46:18+00:00

This patch allows the kernel's struct ops (i.e. func ptr) to be
implemented in BPF.  The first use case in this series is the
"struct tcp_congestion_ops" which will be introduced in a
latter patch.

This patch introduces a new prog type BPF_PROG_TYPE_STRUCT_OPS.
The BPF_PROG_TYPE_STRUCT_OPS prog is verified against a particular
func ptr of a kernel struct.  The attr->attach_btf_id is the btf id
of a kernel struct.  The attr->expected_attach_type is the member
"index" of that kernel struct.  The first member of a struct starts
with member index 0.  That will avoid ambiguity when a kernel struct
has multiple func ptrs with the same func signature.

For example, a BPF_PROG_TYPE_STRUCT_OPS prog is written
to implement the "init" func ptr of the "struct tcp_congestion_ops".
The attr->attach_btf_id is the btf id of the "struct tcp_congestion_ops"
of the _running_ kernel.  The attr->expected_attach_type is 3.

The ctx of BPF_PROG_TYPE_STRUCT_OPS is an array of u64 args saved
by arch_prepare_bpf_trampoline that will be done in the next
patch when introducing BPF_MAP_TYPE_STRUCT_OPS.

"struct bpf_struct_ops" is introduced as a common interface for the kernel
struct that supports BPF_PROG_TYPE_STRUCT_OPS prog.  The supporting kernel
struct will need to implement an instance of the "struct bpf_struct_ops".

The supporting kernel struct also needs to implement a bpf_verifier_ops.
During BPF_PROG_LOAD, bpf_struct_ops_find() will find the right
bpf_verifier_ops by searching the attr->attach_btf_id.

A new "btf_struct_access" is also added to the bpf_verifier_ops such
that the supporting kernel struct can optionally provide its own specific
check on accessing the func arg (e.g. provide limited write access).

After btf_vmlinux is parsed, the new bpf_struct_ops_init() is called
to initialize some values (e.g. the btf id of the supporting kernel
struct) and it can only be done once the btf_vmlinux is available.

The R0 checks at BPF_EXIT is excluded for the BPF_PROG_TYPE_STRUCT_OPS prog
if the return type of the prog->aux->attach_func_proto is "void".

Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov 
Acked-by: Andrii Nakryiko 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20200109003503.3855825-1-kafai@fb.com