cbd3570086
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 <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
369 lines
12 KiB
C
369 lines
12 KiB
C
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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#include <linux/kernel.h>
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/bpf.h>
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#include <linux/filter.h>
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#include <net/netlink.h>
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#include <linux/file.h>
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#include <linux/vmalloc.h>
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/* bpf_check() is a static code analyzer that walks eBPF program
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* instruction by instruction and updates register/stack state.
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* All paths of conditional branches are analyzed until 'bpf_exit' insn.
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*
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* The first pass is depth-first-search to check that the program is a DAG.
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* It rejects the following programs:
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* - larger than BPF_MAXINSNS insns
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* - if loop is present (detected via back-edge)
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* - unreachable insns exist (shouldn't be a forest. program = one function)
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* - out of bounds or malformed jumps
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* The second pass is all possible path descent from the 1st insn.
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* Since it's analyzing all pathes through the program, the length of the
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* analysis is limited to 32k insn, which may be hit even if total number of
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* insn is less then 4K, but there are too many branches that change stack/regs.
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* Number of 'branches to be analyzed' is limited to 1k
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*
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* On entry to each instruction, each register has a type, and the instruction
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* changes the types of the registers depending on instruction semantics.
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* If instruction is BPF_MOV64_REG(BPF_REG_1, BPF_REG_5), then type of R5 is
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* copied to R1.
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*
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* All registers are 64-bit.
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* R0 - return register
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* R1-R5 argument passing registers
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* R6-R9 callee saved registers
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* R10 - frame pointer read-only
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*
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* At the start of BPF program the register R1 contains a pointer to bpf_context
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* and has type PTR_TO_CTX.
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*
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* Verifier tracks arithmetic operations on pointers in case:
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* BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
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* BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -20),
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* 1st insn copies R10 (which has FRAME_PTR) type into R1
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* and 2nd arithmetic instruction is pattern matched to recognize
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* that it wants to construct a pointer to some element within stack.
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* So after 2nd insn, the register R1 has type PTR_TO_STACK
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* (and -20 constant is saved for further stack bounds checking).
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* Meaning that this reg is a pointer to stack plus known immediate constant.
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*
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* Most of the time the registers have UNKNOWN_VALUE type, which
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* means the register has some value, but it's not a valid pointer.
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* (like pointer plus pointer becomes UNKNOWN_VALUE type)
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*
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* When verifier sees load or store instructions the type of base register
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* can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, FRAME_PTR. These are three pointer
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* types recognized by check_mem_access() function.
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*
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* PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
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* and the range of [ptr, ptr + map's value_size) is accessible.
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*
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* registers used to pass values to function calls are checked against
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* function argument constraints.
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*
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* ARG_PTR_TO_MAP_KEY is one of such argument constraints.
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* It means that the register type passed to this function must be
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* PTR_TO_STACK and it will be used inside the function as
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* 'pointer to map element key'
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*
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* For example the argument constraints for bpf_map_lookup_elem():
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* .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
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* .arg1_type = ARG_CONST_MAP_PTR,
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* .arg2_type = ARG_PTR_TO_MAP_KEY,
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*
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* ret_type says that this function returns 'pointer to map elem value or null'
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* function expects 1st argument to be a const pointer to 'struct bpf_map' and
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* 2nd argument should be a pointer to stack, which will be used inside
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* the helper function as a pointer to map element key.
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*
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* On the kernel side the helper function looks like:
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* u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
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* {
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* struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
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* void *key = (void *) (unsigned long) r2;
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* void *value;
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*
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* here kernel can access 'key' and 'map' pointers safely, knowing that
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* [key, key + map->key_size) bytes are valid and were initialized on
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* the stack of eBPF program.
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* }
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*
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* Corresponding eBPF program may look like:
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* BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), // after this insn R2 type is FRAME_PTR
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* BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), // after this insn R2 type is PTR_TO_STACK
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* BPF_LD_MAP_FD(BPF_REG_1, map_fd), // after this insn R1 type is CONST_PTR_TO_MAP
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* BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
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* here verifier looks at prototype of map_lookup_elem() and sees:
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* .arg1_type == ARG_CONST_MAP_PTR and R1->type == CONST_PTR_TO_MAP, which is ok,
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* Now verifier knows that this map has key of R1->map_ptr->key_size bytes
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*
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* Then .arg2_type == ARG_PTR_TO_MAP_KEY and R2->type == PTR_TO_STACK, ok so far,
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* Now verifier checks that [R2, R2 + map's key_size) are within stack limits
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* and were initialized prior to this call.
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* If it's ok, then verifier allows this BPF_CALL insn and looks at
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* .ret_type which is RET_PTR_TO_MAP_VALUE_OR_NULL, so it sets
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* R0->type = PTR_TO_MAP_VALUE_OR_NULL which means bpf_map_lookup_elem() function
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* returns ether pointer to map value or NULL.
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*
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* When type PTR_TO_MAP_VALUE_OR_NULL passes through 'if (reg != 0) goto +off'
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* insn, the register holding that pointer in the true branch changes state to
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* PTR_TO_MAP_VALUE and the same register changes state to CONST_IMM in the false
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* branch. See check_cond_jmp_op().
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*
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* After the call R0 is set to return type of the function and registers R1-R5
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* are set to NOT_INIT to indicate that they are no longer readable.
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*/
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/* single container for all structs
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* one verifier_env per bpf_check() call
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*/
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struct verifier_env {
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};
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/* verbose verifier prints what it's seeing
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* bpf_check() is called under lock, so no race to access these global vars
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*/
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static u32 log_level, log_size, log_len;
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static char *log_buf;
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static DEFINE_MUTEX(bpf_verifier_lock);
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/* log_level controls verbosity level of eBPF verifier.
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* verbose() is used to dump the verification trace to the log, so the user
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* can figure out what's wrong with the program
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*/
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static void verbose(const char *fmt, ...)
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{
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va_list args;
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if (log_level == 0 || log_len >= log_size - 1)
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return;
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va_start(args, fmt);
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log_len += vscnprintf(log_buf + log_len, log_size - log_len, fmt, args);
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va_end(args);
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}
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static const char *const bpf_class_string[] = {
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[BPF_LD] = "ld",
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[BPF_LDX] = "ldx",
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[BPF_ST] = "st",
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[BPF_STX] = "stx",
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[BPF_ALU] = "alu",
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[BPF_JMP] = "jmp",
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[BPF_RET] = "BUG",
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[BPF_ALU64] = "alu64",
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};
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static const char *const bpf_alu_string[] = {
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[BPF_ADD >> 4] = "+=",
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[BPF_SUB >> 4] = "-=",
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[BPF_MUL >> 4] = "*=",
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[BPF_DIV >> 4] = "/=",
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[BPF_OR >> 4] = "|=",
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[BPF_AND >> 4] = "&=",
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[BPF_LSH >> 4] = "<<=",
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[BPF_RSH >> 4] = ">>=",
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[BPF_NEG >> 4] = "neg",
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[BPF_MOD >> 4] = "%=",
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[BPF_XOR >> 4] = "^=",
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[BPF_MOV >> 4] = "=",
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[BPF_ARSH >> 4] = "s>>=",
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[BPF_END >> 4] = "endian",
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};
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static const char *const bpf_ldst_string[] = {
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[BPF_W >> 3] = "u32",
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[BPF_H >> 3] = "u16",
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[BPF_B >> 3] = "u8",
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[BPF_DW >> 3] = "u64",
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};
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static const char *const bpf_jmp_string[] = {
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[BPF_JA >> 4] = "jmp",
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[BPF_JEQ >> 4] = "==",
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[BPF_JGT >> 4] = ">",
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[BPF_JGE >> 4] = ">=",
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[BPF_JSET >> 4] = "&",
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[BPF_JNE >> 4] = "!=",
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[BPF_JSGT >> 4] = "s>",
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[BPF_JSGE >> 4] = "s>=",
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[BPF_CALL >> 4] = "call",
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[BPF_EXIT >> 4] = "exit",
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};
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static void print_bpf_insn(struct bpf_insn *insn)
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{
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u8 class = BPF_CLASS(insn->code);
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if (class == BPF_ALU || class == BPF_ALU64) {
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if (BPF_SRC(insn->code) == BPF_X)
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verbose("(%02x) %sr%d %s %sr%d\n",
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insn->code, class == BPF_ALU ? "(u32) " : "",
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insn->dst_reg,
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bpf_alu_string[BPF_OP(insn->code) >> 4],
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class == BPF_ALU ? "(u32) " : "",
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insn->src_reg);
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else
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verbose("(%02x) %sr%d %s %s%d\n",
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insn->code, class == BPF_ALU ? "(u32) " : "",
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insn->dst_reg,
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bpf_alu_string[BPF_OP(insn->code) >> 4],
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class == BPF_ALU ? "(u32) " : "",
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insn->imm);
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} else if (class == BPF_STX) {
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if (BPF_MODE(insn->code) == BPF_MEM)
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verbose("(%02x) *(%s *)(r%d %+d) = r%d\n",
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insn->code,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->dst_reg,
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insn->off, insn->src_reg);
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else if (BPF_MODE(insn->code) == BPF_XADD)
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verbose("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
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insn->code,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->dst_reg, insn->off,
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insn->src_reg);
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else
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verbose("BUG_%02x\n", insn->code);
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} else if (class == BPF_ST) {
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if (BPF_MODE(insn->code) != BPF_MEM) {
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verbose("BUG_st_%02x\n", insn->code);
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return;
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}
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verbose("(%02x) *(%s *)(r%d %+d) = %d\n",
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insn->code,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->dst_reg,
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insn->off, insn->imm);
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} else if (class == BPF_LDX) {
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if (BPF_MODE(insn->code) != BPF_MEM) {
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verbose("BUG_ldx_%02x\n", insn->code);
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return;
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}
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verbose("(%02x) r%d = *(%s *)(r%d %+d)\n",
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insn->code, insn->dst_reg,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->src_reg, insn->off);
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} else if (class == BPF_LD) {
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if (BPF_MODE(insn->code) == BPF_ABS) {
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verbose("(%02x) r0 = *(%s *)skb[%d]\n",
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insn->code,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->imm);
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} else if (BPF_MODE(insn->code) == BPF_IND) {
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verbose("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
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insn->code,
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bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
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insn->src_reg, insn->imm);
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} else if (BPF_MODE(insn->code) == BPF_IMM) {
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verbose("(%02x) r%d = 0x%x\n",
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insn->code, insn->dst_reg, insn->imm);
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} else {
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verbose("BUG_ld_%02x\n", insn->code);
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return;
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}
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} else if (class == BPF_JMP) {
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u8 opcode = BPF_OP(insn->code);
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if (opcode == BPF_CALL) {
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verbose("(%02x) call %d\n", insn->code, insn->imm);
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} else if (insn->code == (BPF_JMP | BPF_JA)) {
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verbose("(%02x) goto pc%+d\n",
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insn->code, insn->off);
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} else if (insn->code == (BPF_JMP | BPF_EXIT)) {
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verbose("(%02x) exit\n", insn->code);
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} else if (BPF_SRC(insn->code) == BPF_X) {
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verbose("(%02x) if r%d %s r%d goto pc%+d\n",
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insn->code, insn->dst_reg,
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bpf_jmp_string[BPF_OP(insn->code) >> 4],
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insn->src_reg, insn->off);
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} else {
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verbose("(%02x) if r%d %s 0x%x goto pc%+d\n",
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insn->code, insn->dst_reg,
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bpf_jmp_string[BPF_OP(insn->code) >> 4],
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insn->imm, insn->off);
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}
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} else {
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verbose("(%02x) %s\n", insn->code, bpf_class_string[class]);
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}
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}
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int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
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{
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char __user *log_ubuf = NULL;
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struct verifier_env *env;
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int ret = -EINVAL;
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if (prog->len <= 0 || prog->len > BPF_MAXINSNS)
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return -E2BIG;
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/* 'struct verifier_env' can be global, but since it's not small,
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* allocate/free it every time bpf_check() is called
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*/
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env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
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if (!env)
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return -ENOMEM;
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/* grab the mutex to protect few globals used by verifier */
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mutex_lock(&bpf_verifier_lock);
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if (attr->log_level || attr->log_buf || attr->log_size) {
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/* user requested verbose verifier output
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* and supplied buffer to store the verification trace
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*/
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log_level = attr->log_level;
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log_ubuf = (char __user *) (unsigned long) attr->log_buf;
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log_size = attr->log_size;
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log_len = 0;
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ret = -EINVAL;
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/* log_* values have to be sane */
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if (log_size < 128 || log_size > UINT_MAX >> 8 ||
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log_level == 0 || log_ubuf == NULL)
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goto free_env;
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ret = -ENOMEM;
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log_buf = vmalloc(log_size);
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if (!log_buf)
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goto free_env;
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} else {
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log_level = 0;
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}
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/* ret = do_check(env); */
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if (log_level && log_len >= log_size - 1) {
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BUG_ON(log_len >= log_size);
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/* verifier log exceeded user supplied buffer */
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ret = -ENOSPC;
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/* fall through to return what was recorded */
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}
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/* copy verifier log back to user space including trailing zero */
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if (log_level && copy_to_user(log_ubuf, log_buf, log_len + 1) != 0) {
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ret = -EFAULT;
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goto free_log_buf;
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}
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free_log_buf:
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if (log_level)
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vfree(log_buf);
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free_env:
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kfree(env);
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mutex_unlock(&bpf_verifier_lock);
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return ret;
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}
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