linux-stable.git/kernel/bpf/verifier.c, branch linux-4.0.y

ebpf: verifier: check that call reg with ARG_ANYTHING is initialized

2015-05-06T20:04:07+00:00

commit 80f1d68ccba70b1060c9c7360ca83da430f66bed upstream.

I noticed that a helper function with argument type ARG_ANYTHING does
not need to have an initialized value (register).

This can worst case lead to unintented stack memory leakage in future
helper functions if they are not carefully designed, or unintended
application behaviour in case the application developer was not careful
enough to match a correct helper function signature in the API.

The underlying issue is that ARG_ANYTHING should actually be split
into two different semantics:

  1) ARG_DONTCARE for function arguments that the helper function
     does not care about (in other words: the default for unused
     function arguments), and

  2) ARG_ANYTHING that is an argument actually being used by a
     helper function and *guaranteed* to be an initialized register.

The current risk is low: ARG_ANYTHING is only used for the 'flags'
argument (r4) in bpf_map_update_elem() that internally does strict
checking.

Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)")
Signed-off-by: Daniel Borkmann 
Acked-by: Alexei Starovoitov 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

bpf: fix verifier memory corruption

2015-04-29T08:22:18+00:00

[ Upstream commit c3de6317d748e23b9e46ba36e10483728d00d144 ]

Due to missing bounds check the DAG pass of the BPF verifier can corrupt
the memory which can cause random crashes during program loading:

[8.449451] BUG: unable to handle kernel paging request at ffffffffffffffff
[8.451293] IP: [] kmem_cache_alloc_trace+0x8d/0x2f0
[8.452329] Oops: 0000 [#1] SMP
[8.452329] Call Trace:
[8.452329]  [] bpf_check+0x852/0x2000
[8.452329]  [] bpf_prog_load+0x1e4/0x310
[8.452329]  [] ? might_fault+0x5f/0xb0
[8.452329]  [] SyS_bpf+0x806/0xa30

Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
Signed-off-by: Alexei Starovoitov 
Acked-by: Hannes Frederic Sowa 
Acked-by: Daniel Borkmann 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

bpf: verifier: add checks for BPF_ABS | BPF_IND instructions

2014-12-06T05:47:32+00:00

introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used
for attaching programs to sockets where ctx == skb.

add verifier checks for ABS/IND instructions which can only be seen
in socket filters, therefore the check:
  if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER)
    verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n");

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: reduce verifier memory consumption

2014-10-30T19:44:37+00:00

verifier keeps track of register state spilled to stack.
registers are 8-byte wide and always aligned, so instead of tracking them
in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track
spilled register state.
Though verifier runs in user context and its state freed immediately
after verification, it makes sense to reduce its memory usage.
This optimization reduces sizeof(struct verifier_state)
from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit.

Note, this patch doesn't change existing limits, which are there to bound
time and memory during verification: 4k total number of insns in a program,
1k number of jumps (states to visit) and 32k number of processed insn
(since an insn may be visited multiple times). Theoretical worst case memory
during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers
cleanup and rejects the program.

Suggested-by: Andy Lutomirski 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: fix bug in eBPF verifier

2014-10-22T01:43:46+00:00

while comparing for verifier state equivalency the comparison
was missing a check for uninitialized register.
Make sure it does so and add a testcase.

Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
Cc: Hannes Frederic Sowa 
Signed-off-by: Alexei Starovoitov 
Acked-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

bpf: add search pruning optimization to verifier

2014-10-02T01:30:33+00:00

consider C program represented in eBPF:
int filter(int arg)
{
    int a, b, c, *ptr;

    if (arg == 1)
        ptr = &a;
    else if (arg == 2)
        ptr = &b;
    else
        ptr = &c;

    *ptr = 0;
    return 0;
}
eBPF verifier has to follow all possible paths through the program
to recognize that '*ptr = 0' instruction would be safe to execute
in all situations.
It's doing it by picking a path towards the end and observes changes
to registers and stack at every insn until it reaches bpf_exit.
Then it comes back to one of the previous branches and goes towards
the end again with potentially different values in registers.
When program has a lot of branches, the number of possible combinations
of branches is huge, so verifer has a hard limit of walking no more
than 32k instructions. This limit can be reached and complex (but valid)
programs could be rejected. Therefore it's important to recognize equivalent
verifier states to prune this depth first search.

Basic idea can be illustrated by the program (where .. are some eBPF insns):
    1: ..
    2: if (rX == rY) goto 4
    3: ..
    4: ..
    5: ..
    6: bpf_exit
In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6
Since insn#2 is a branch the verifier will remember its state in verifier stack
to come back to it later.
Since insn#4 is marked as 'branch target', the verifier will remember its state
in explored_states[4] linked list.
Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and
will continue.
Without search pruning optimization verifier would have to walk 4, 5, 6 again,
effectively simulating execution of insns 1, 2, 4, 5, 6
With search pruning it will check whether state at #4 after jumping from #2
is equivalent to one recorded in explored_states[4] during first pass.
If there is an equivalent state, verifier can prune the search at #4 and declare
this path to be safe as well.
In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns
and 1, 2, 4 insns produces equivalent registers and stack.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: verifier (add verifier core)

2014-09-26T19:05:15+00:00

This patch adds verifier core which simulates execution of every insn and
records the state of registers and program stack. Every branch instruction seen
during simulation is pushed into state stack. When verifier reaches BPF_EXIT,
it pops the state from the stack and continues until it reaches BPF_EXIT again.
For program:
1: bpf_mov r1, xxx
2: if (r1 == 0) goto 5
3: bpf_mov r0, 1
4: goto 6
5: bpf_mov r0, 2
6: bpf_exit
The verifier will walk insns: 1, 2, 3, 4, 6
then it will pop the state recorded at insn#2 and will continue: 5, 6

This way it walks all possible paths through the program and checks all
possible values of registers. While doing so, it checks for:
- invalid instructions
- uninitialized register access
- uninitialized stack access
- misaligned stack access
- out of range stack access
- invalid calling convention
- instruction encoding is not using reserved fields

Kernel subsystem configures the verifier with two callbacks:

- bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
  that provides information to the verifer which fields of 'ctx'
  are accessible (remember 'ctx' is the first argument to eBPF program)

- const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id);
  returns argument constraints of kernel helper functions that eBPF program
  may call, so that verifier can checks that R1-R5 types match the prototype

More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: verifier (add branch/goto checks)

2014-09-26T19:05:15+00:00

check that control flow graph of eBPF program is a directed acyclic graph

check_cfg() does:
- detect loops
- detect unreachable instructions
- check that program terminates with BPF_EXIT insn
- check that all branches are within program boundary

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: handle pseudo BPF_LD_IMM64 insn

2014-09-26T19:05:15+00:00

eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions
to refer to process-local map_fd. Scan the program for such instructions and
if FDs are valid, convert them to 'struct bpf_map' pointers which will be used
by verifier to check access to maps in bpf_map_lookup/update() calls.
If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping
BPF_PSEUDO_MAP_FD flag.

Note that eBPF interpreter is generic and knows nothing about pseudo insns.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller

bpf: verifier (add ability to receive verification log)

2014-09-26T19:05:15+00:00

add optional attributes for BPF_PROG_LOAD syscall:
union bpf_attr {
    struct {
	...
	__u32         log_level; /* verbosity level of eBPF verifier */
	__u32         log_size;  /* size of user buffer */
	__aligned_u64 log_buf;   /* user supplied 'char *buffer' */
    };
};

when log_level > 0 the verifier will return its verification log in the user
supplied buffer 'log_buf' which can be used by program author to analyze why
verifier rejected given program.

'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt
provides several examples of these messages, like the program:

  BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
  BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
  BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
  BPF_LD_MAP_FD(BPF_REG_1, 0),
  BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem),
  BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
  BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0),
  BPF_EXIT_INSN(),

will be rejected with the following multi-line message in log_buf:

  0: (7a) *(u64 *)(r10 -8) = 0
  1: (bf) r2 = r10
  2: (07) r2 += -8
  3: (b7) r1 = 0
  4: (85) call 1
  5: (15) if r0 == 0x0 goto pc+1
   R0=map_ptr R10=fp
  6: (7a) *(u64 *)(r0 +4) = 0
  misaligned access off 4 size 8

The format of the output can change at any time as verifier evolves.

Signed-off-by: Alexei Starovoitov 
Signed-off-by: David S. Miller