456 lines
11 KiB
C
456 lines
11 KiB
C
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/*
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* bpf-prologue.c
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*
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* Copyright (C) 2015 He Kuang <hekuang@huawei.com>
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* Copyright (C) 2015 Wang Nan <wangnan0@huawei.com>
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* Copyright (C) 2015 Huawei Inc.
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*/
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#include <bpf/libbpf.h>
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#include "perf.h"
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#include "debug.h"
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#include "bpf-loader.h"
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#include "bpf-prologue.h"
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#include "probe-finder.h"
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#include <dwarf-regs.h>
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#include <linux/filter.h>
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#define BPF_REG_SIZE 8
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#define JMP_TO_ERROR_CODE -1
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#define JMP_TO_SUCCESS_CODE -2
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#define JMP_TO_USER_CODE -3
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struct bpf_insn_pos {
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struct bpf_insn *begin;
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struct bpf_insn *end;
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struct bpf_insn *pos;
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};
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static inline int
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pos_get_cnt(struct bpf_insn_pos *pos)
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{
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return pos->pos - pos->begin;
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}
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static int
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append_insn(struct bpf_insn new_insn, struct bpf_insn_pos *pos)
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{
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if (!pos->pos)
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return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
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if (pos->pos + 1 >= pos->end) {
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pr_err("bpf prologue: prologue too long\n");
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pos->pos = NULL;
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return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
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}
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*(pos->pos)++ = new_insn;
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return 0;
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}
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static int
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check_pos(struct bpf_insn_pos *pos)
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{
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if (!pos->pos || pos->pos >= pos->end)
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return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
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return 0;
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}
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/* Give it a shorter name */
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#define ins(i, p) append_insn((i), (p))
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/*
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* Give a register name (in 'reg'), generate instruction to
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* load register into an eBPF register rd:
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* 'ldd target_reg, offset(ctx_reg)', where:
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* ctx_reg is pre initialized to pointer of 'struct pt_regs'.
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*/
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static int
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gen_ldx_reg_from_ctx(struct bpf_insn_pos *pos, int ctx_reg,
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const char *reg, int target_reg)
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{
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int offset = regs_query_register_offset(reg);
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if (offset < 0) {
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pr_err("bpf: prologue: failed to get register %s\n",
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reg);
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return offset;
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}
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ins(BPF_LDX_MEM(BPF_DW, target_reg, ctx_reg, offset), pos);
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return check_pos(pos);
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}
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/*
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* Generate a BPF_FUNC_probe_read function call.
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*
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* src_base_addr_reg is a register holding base address,
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* dst_addr_reg is a register holding dest address (on stack),
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* result is:
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*
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* *[dst_addr_reg] = *([src_base_addr_reg] + offset)
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*
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* Arguments of BPF_FUNC_probe_read:
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* ARG1: ptr to stack (dest)
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* ARG2: size (8)
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* ARG3: unsafe ptr (src)
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*/
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static int
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gen_read_mem(struct bpf_insn_pos *pos,
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int src_base_addr_reg,
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int dst_addr_reg,
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long offset)
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{
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/* mov arg3, src_base_addr_reg */
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if (src_base_addr_reg != BPF_REG_ARG3)
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ins(BPF_MOV64_REG(BPF_REG_ARG3, src_base_addr_reg), pos);
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/* add arg3, #offset */
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if (offset)
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ins(BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG3, offset), pos);
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/* mov arg2, #reg_size */
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ins(BPF_ALU64_IMM(BPF_MOV, BPF_REG_ARG2, BPF_REG_SIZE), pos);
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/* mov arg1, dst_addr_reg */
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if (dst_addr_reg != BPF_REG_ARG1)
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ins(BPF_MOV64_REG(BPF_REG_ARG1, dst_addr_reg), pos);
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/* Call probe_read */
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ins(BPF_EMIT_CALL(BPF_FUNC_probe_read), pos);
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/*
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* Error processing: if read fail, goto error code,
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* will be relocated. Target should be the start of
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* error processing code.
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*/
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ins(BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, JMP_TO_ERROR_CODE),
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pos);
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return check_pos(pos);
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}
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/*
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* Each arg should be bare register. Fetch and save them into argument
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* registers (r3 - r5).
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*
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* BPF_REG_1 should have been initialized with pointer to
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* 'struct pt_regs'.
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*/
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static int
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gen_prologue_fastpath(struct bpf_insn_pos *pos,
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struct probe_trace_arg *args, int nargs)
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{
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int i, err = 0;
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for (i = 0; i < nargs; i++) {
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err = gen_ldx_reg_from_ctx(pos, BPF_REG_1, args[i].value,
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BPF_PROLOGUE_START_ARG_REG + i);
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if (err)
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goto errout;
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}
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return check_pos(pos);
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errout:
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return err;
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}
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/*
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* Slow path:
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* At least one argument has the form of 'offset($rx)'.
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*
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* Following code first stores them into stack, then loads all of then
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* to r2 - r5.
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* Before final loading, the final result should be:
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*
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* low address
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* BPF_REG_FP - 24 ARG3
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* BPF_REG_FP - 16 ARG2
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* BPF_REG_FP - 8 ARG1
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* BPF_REG_FP
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* high address
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*
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* For each argument (described as: offn(...off2(off1(reg)))),
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* generates following code:
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*
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* r7 <- fp
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* r7 <- r7 - stack_offset // Ideal code should initialize r7 using
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* // fp before generating args. However,
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* // eBPF won't regard r7 as stack pointer
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* // if it is generated by minus 8 from
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* // another stack pointer except fp.
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* // This is why we have to set r7
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* // to fp for each variable.
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* r3 <- value of 'reg'-> generated using gen_ldx_reg_from_ctx()
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* (r7) <- r3 // skip following instructions for bare reg
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* r3 <- r3 + off1 . // skip if off1 == 0
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* r2 <- 8 \
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* r1 <- r7 |-> generated by gen_read_mem()
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* call probe_read /
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* jnei r0, 0, err ./
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* r3 <- (r7)
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* r3 <- r3 + off2 . // skip if off2 == 0
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* r2 <- 8 \ // r2 may be broken by probe_read, so set again
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* r1 <- r7 |-> generated by gen_read_mem()
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* call probe_read /
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* jnei r0, 0, err ./
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* ...
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*/
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static int
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gen_prologue_slowpath(struct bpf_insn_pos *pos,
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struct probe_trace_arg *args, int nargs)
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{
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int err, i;
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for (i = 0; i < nargs; i++) {
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struct probe_trace_arg *arg = &args[i];
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const char *reg = arg->value;
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struct probe_trace_arg_ref *ref = NULL;
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int stack_offset = (i + 1) * -8;
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pr_debug("prologue: fetch arg %d, base reg is %s\n",
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i, reg);
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/* value of base register is stored into ARG3 */
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err = gen_ldx_reg_from_ctx(pos, BPF_REG_CTX, reg,
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BPF_REG_ARG3);
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if (err) {
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pr_err("prologue: failed to get offset of register %s\n",
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reg);
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goto errout;
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}
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/* Make r7 the stack pointer. */
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ins(BPF_MOV64_REG(BPF_REG_7, BPF_REG_FP), pos);
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/* r7 += -8 */
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ins(BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, stack_offset), pos);
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/*
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* Store r3 (base register) onto stack
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* Ensure fp[offset] is set.
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* fp is the only valid base register when storing
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* into stack. We are not allowed to use r7 as base
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* register here.
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*/
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ins(BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_ARG3,
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stack_offset), pos);
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ref = arg->ref;
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while (ref) {
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pr_debug("prologue: arg %d: offset %ld\n",
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i, ref->offset);
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err = gen_read_mem(pos, BPF_REG_3, BPF_REG_7,
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ref->offset);
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if (err) {
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pr_err("prologue: failed to generate probe_read function call\n");
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goto errout;
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}
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ref = ref->next;
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/*
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* Load previous result into ARG3. Use
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* BPF_REG_FP instead of r7 because verifier
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* allows FP based addressing only.
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*/
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if (ref)
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ins(BPF_LDX_MEM(BPF_DW, BPF_REG_ARG3,
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BPF_REG_FP, stack_offset), pos);
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}
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}
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/* Final pass: read to registers */
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for (i = 0; i < nargs; i++)
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ins(BPF_LDX_MEM(BPF_DW, BPF_PROLOGUE_START_ARG_REG + i,
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BPF_REG_FP, -BPF_REG_SIZE * (i + 1)), pos);
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ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_SUCCESS_CODE), pos);
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return check_pos(pos);
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errout:
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return err;
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}
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static int
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prologue_relocate(struct bpf_insn_pos *pos, struct bpf_insn *error_code,
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struct bpf_insn *success_code, struct bpf_insn *user_code)
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{
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struct bpf_insn *insn;
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if (check_pos(pos))
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return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
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for (insn = pos->begin; insn < pos->pos; insn++) {
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struct bpf_insn *target;
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u8 class = BPF_CLASS(insn->code);
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u8 opcode;
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if (class != BPF_JMP)
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continue;
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opcode = BPF_OP(insn->code);
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if (opcode == BPF_CALL)
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continue;
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switch (insn->off) {
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case JMP_TO_ERROR_CODE:
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target = error_code;
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break;
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case JMP_TO_SUCCESS_CODE:
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target = success_code;
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break;
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case JMP_TO_USER_CODE:
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target = user_code;
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break;
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default:
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pr_err("bpf prologue: internal error: relocation failed\n");
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return -BPF_LOADER_ERRNO__PROLOGUE;
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}
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insn->off = target - (insn + 1);
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}
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return 0;
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}
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int bpf__gen_prologue(struct probe_trace_arg *args, int nargs,
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struct bpf_insn *new_prog, size_t *new_cnt,
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size_t cnt_space)
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{
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struct bpf_insn *success_code = NULL;
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struct bpf_insn *error_code = NULL;
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struct bpf_insn *user_code = NULL;
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struct bpf_insn_pos pos;
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bool fastpath = true;
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int err = 0, i;
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if (!new_prog || !new_cnt)
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return -EINVAL;
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if (cnt_space > BPF_MAXINSNS)
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cnt_space = BPF_MAXINSNS;
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pos.begin = new_prog;
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pos.end = new_prog + cnt_space;
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pos.pos = new_prog;
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if (!nargs) {
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ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 0),
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&pos);
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if (check_pos(&pos))
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goto errout;
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*new_cnt = pos_get_cnt(&pos);
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return 0;
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}
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if (nargs > BPF_PROLOGUE_MAX_ARGS) {
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pr_warning("bpf: prologue: %d arguments are dropped\n",
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nargs - BPF_PROLOGUE_MAX_ARGS);
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nargs = BPF_PROLOGUE_MAX_ARGS;
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}
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/* First pass: validation */
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for (i = 0; i < nargs; i++) {
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struct probe_trace_arg_ref *ref = args[i].ref;
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if (args[i].value[0] == '@') {
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/* TODO: fetch global variable */
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pr_err("bpf: prologue: global %s%+ld not support\n",
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args[i].value, ref ? ref->offset : 0);
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return -ENOTSUP;
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}
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while (ref) {
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/* fastpath is true if all args has ref == NULL */
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fastpath = false;
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/*
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* Instruction encodes immediate value using
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* s32, ref->offset is long. On systems which
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* can't fill long in s32, refuse to process if
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* ref->offset too large (or small).
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*/
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#ifdef __LP64__
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#define OFFSET_MAX ((1LL << 31) - 1)
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||
|
|
#define OFFSET_MIN ((1LL << 31) * -1)
|
||
|
|
if (ref->offset > OFFSET_MAX ||
|
||
|
|
ref->offset < OFFSET_MIN) {
|
||
|
|
pr_err("bpf: prologue: offset out of bound: %ld\n",
|
||
|
|
ref->offset);
|
||
|
|
return -BPF_LOADER_ERRNO__PROLOGUEOOB;
|
||
|
|
}
|
||
|
|
#endif
|
||
|
|
ref = ref->next;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
pr_debug("prologue: pass validation\n");
|
||
|
|
|
||
|
|
if (fastpath) {
|
||
|
|
/* If all variables are registers... */
|
||
|
|
pr_debug("prologue: fast path\n");
|
||
|
|
err = gen_prologue_fastpath(&pos, args, nargs);
|
||
|
|
if (err)
|
||
|
|
goto errout;
|
||
|
|
} else {
|
||
|
|
pr_debug("prologue: slow path\n");
|
||
|
|
|
||
|
|
/* Initialization: move ctx to a callee saved register. */
|
||
|
|
ins(BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1), &pos);
|
||
|
|
|
||
|
|
err = gen_prologue_slowpath(&pos, args, nargs);
|
||
|
|
if (err)
|
||
|
|
goto errout;
|
||
|
|
/*
|
||
|
|
* start of ERROR_CODE (only slow pass needs error code)
|
||
|
|
* mov r2 <- 1 // r2 is error number
|
||
|
|
* mov r3 <- 0 // r3, r4... should be touched or
|
||
|
|
* // verifier would complain
|
||
|
|
* mov r4 <- 0
|
||
|
|
* ...
|
||
|
|
* goto usercode
|
||
|
|
*/
|
||
|
|
error_code = pos.pos;
|
||
|
|
ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 1),
|
||
|
|
&pos);
|
||
|
|
|
||
|
|
for (i = 0; i < nargs; i++)
|
||
|
|
ins(BPF_ALU64_IMM(BPF_MOV,
|
||
|
|
BPF_PROLOGUE_START_ARG_REG + i,
|
||
|
|
0),
|
||
|
|
&pos);
|
||
|
|
ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_USER_CODE),
|
||
|
|
&pos);
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* start of SUCCESS_CODE:
|
||
|
|
* mov r2 <- 0
|
||
|
|
* goto usercode // skip
|
||
|
|
*/
|
||
|
|
success_code = pos.pos;
|
||
|
|
ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 0), &pos);
|
||
|
|
|
||
|
|
/*
|
||
|
|
* start of USER_CODE:
|
||
|
|
* Restore ctx to r1
|
||
|
|
*/
|
||
|
|
user_code = pos.pos;
|
||
|
|
if (!fastpath) {
|
||
|
|
/*
|
||
|
|
* Only slow path needs restoring of ctx. In fast path,
|
||
|
|
* register are loaded directly from r1.
|
||
|
|
*/
|
||
|
|
ins(BPF_MOV64_REG(BPF_REG_ARG1, BPF_REG_CTX), &pos);
|
||
|
|
err = prologue_relocate(&pos, error_code, success_code,
|
||
|
|
user_code);
|
||
|
|
if (err)
|
||
|
|
goto errout;
|
||
|
|
}
|
||
|
|
|
||
|
|
err = check_pos(&pos);
|
||
|
|
if (err)
|
||
|
|
goto errout;
|
||
|
|
|
||
|
|
*new_cnt = pos_get_cnt(&pos);
|
||
|
|
return 0;
|
||
|
|
errout:
|
||
|
|
return err;
|
||
|
|
}
|