LXR linux/arch/mips/net/bpf_jit

   1/*
   2 * bpf_jib_asm.S: Packet/header access helper functions for MIPS/MIPS64 BPF
   3 * compiler.
   4 *
   5 * Copyright (C) 2015 Imagination Technologies Ltd.
   6 * Author: Markos Chandras <markos.chandras@imgtec.com>
   7 *
   8 * This program is free software; you can redistribute it and/or modify it
   9 * under the terms of the GNU General Public License as published by the
  10 * Free Software Foundation; version 2 of the License.
  11 */
  12
  13#include <asm/asm.h>
  14#include <asm/regdef.h>
  15#include "bpf_jit.h"
  16
  17/* ABI
  18 *
  19 * r_skb_hl     skb header length
  20 * r_skb_data   skb data
  21 * r_off(a1)    offset register
  22 * r_A          BPF register A
  23 * r_X          PF register X
  24 * r_skb(a0)    *skb
  25 * r_M          *scratch memory
  26 * r_skb_le     skb length
  27 * r_s0         Scratch register 0
  28 * r_s1         Scratch register 1
  29 *
  30 * On entry:
  31 * a0: *skb
  32 * a1: offset (imm or imm + X)
  33 *
  34 * All non-BPF-ABI registers are free for use. On return, we only
  35 * care about r_ret. The BPF-ABI registers are assumed to remain
  36 * unmodified during the entire filter operation.
  37 */
  38
  39#define skb     a0
  40#define offset  a1
  41#define SKF_LL_OFF  (-0x200000) /* Can't include linux/filter.h in assembly */
  42
  43        /* We know better :) so prevent assembler reordering etc */
  44        .set    noreorder
  45
  46#define is_offset_negative(TYPE)                                \
  47        /* If offset is negative we have more work to do */     \
  48        slti    t0, offset, 0;                                  \
  49        bgtz    t0, bpf_slow_path_##TYPE##_neg;                 \
  50        /* Be careful what follows in DS. */
  51
  52#define is_offset_in_header(SIZE, TYPE)                         \
  53        /* Reading from header? */                              \
  54        addiu   $r_s0, $r_skb_hl, -SIZE;                        \
  55        slt     t0, $r_s0, offset;                              \
  56        bgtz    t0, bpf_slow_path_##TYPE;                       \
  57
  58LEAF(sk_load_word)
  59        is_offset_negative(word)
  60        .globl sk_load_word_positive
  61sk_load_word_positive:
  62        is_offset_in_header(4, word)
  63        /* Offset within header boundaries */
  64        PTR_ADDU t1, $r_skb_data, offset
  65        lw      $r_A, 0(t1)
  66#ifdef CONFIG_CPU_LITTLE_ENDIAN
  67        wsbh    t0, $r_A
  68        rotr    $r_A, t0, 16
  69#endif
  70        jr      $r_ra
  71         move   $r_ret, zero
  72        END(sk_load_word)
  73
  74LEAF(sk_load_half)
  75        is_offset_negative(half)
  76        .globl sk_load_half_positive
  77sk_load_half_positive:
  78        is_offset_in_header(2, half)
  79        /* Offset within header boundaries */
  80        PTR_ADDU t1, $r_skb_data, offset
  81        lh      $r_A, 0(t1)
  82#ifdef CONFIG_CPU_LITTLE_ENDIAN
  83        wsbh    t0, $r_A
  84        seh     $r_A, t0
  85#endif
  86        jr      $r_ra
  87         move   $r_ret, zero
  88        END(sk_load_half)
  89
  90LEAF(sk_load_byte)
  91        is_offset_negative(byte)
  92        .globl sk_load_byte_positive
  93sk_load_byte_positive:
  94        is_offset_in_header(1, byte)
  95        /* Offset within header boundaries */
  96        PTR_ADDU t1, $r_skb_data, offset
  97        lb      $r_A, 0(t1)
  98        jr      $r_ra
  99         move   $r_ret, zero
 100        END(sk_load_byte)
 101
 102/*
 103 * call skb_copy_bits:
 104 * (prototype in linux/skbuff.h)
 105 *
 106 * int skb_copy_bits(sk_buff *skb, int offset, void *to, int len)
 107 *
 108 * o32 mandates we leave 4 spaces for argument registers in case
 109 * the callee needs to use them. Even though we don't care about
 110 * the argument registers ourselves, we need to allocate that space
 111 * to remain ABI compliant since the callee may want to use that space.
 112 * We also allocate 2 more spaces for $r_ra and our return register (*to).
 113 *
 114 * n64 is a bit different. The *caller* will allocate the space to preserve
 115 * the arguments. So in 64-bit kernels, we allocate the 4-arg space for no
 116 * good reason but it does not matter that much really.
 117 *
 118 * (void *to) is returned in r_s0
 119 *
 120 */
 121#define bpf_slow_path_common(SIZE)                              \
 122        /* Quick check. Are we within reasonable boundaries? */ \
 123        LONG_ADDIU      $r_s1, $r_skb_len, -SIZE;               \
 124        sltu            $r_s0, offset, $r_s1;                   \
 125        beqz            $r_s0, fault;                           \
 126        /* Load 4th argument in DS */                           \
 127         LONG_ADDIU     a3, zero, SIZE;                         \
 128        PTR_ADDIU       $r_sp, $r_sp, -(6 * SZREG);             \
 129        PTR_LA          t0, skb_copy_bits;                      \
 130        PTR_S           $r_ra, (5 * SZREG)($r_sp);              \
 131        /* Assign low slot to a2 */                             \
 132        move            a2, $r_sp;                              \
 133        jalr            t0;                                     \
 134        /* Reset our destination slot (DS but it's ok) */       \
 135         INT_S          zero, (4 * SZREG)($r_sp);               \
 136        /*                                                      \
 137         * skb_copy_bits returns 0 on success and -EFAULT       \
 138         * on error. Our data live in a2. Do not bother with    \
 139         * our data if an error has been returned.              \
 140         */                                                     \
 141        /* Restore our frame */                                 \
 142        PTR_L           $r_ra, (5 * SZREG)($r_sp);              \
 143        INT_L           $r_s0, (4 * SZREG)($r_sp);              \
 144        bltz            v0, fault;                              \
 145         PTR_ADDIU      $r_sp, $r_sp, 6 * SZREG;                \
 146        move            $r_ret, zero;                           \
 147
 148NESTED(bpf_slow_path_word, (6 * SZREG), $r_sp)
 149        bpf_slow_path_common(4)
 150#ifdef CONFIG_CPU_LITTLE_ENDIAN
 151        wsbh    t0, $r_s0
 152        jr      $r_ra
 153         rotr   $r_A, t0, 16
 154#endif
 155        jr      $r_ra
 156        move    $r_A, $r_s0
 157
 158        END(bpf_slow_path_word)
 159
 160NESTED(bpf_slow_path_half, (6 * SZREG), $r_sp)
 161        bpf_slow_path_common(2)
 162#ifdef CONFIG_CPU_LITTLE_ENDIAN
 163        jr      $r_ra
 164         wsbh   $r_A, $r_s0
 165#endif
 166        jr      $r_ra
 167         move   $r_A, $r_s0
 168
 169        END(bpf_slow_path_half)
 170
 171NESTED(bpf_slow_path_byte, (6 * SZREG), $r_sp)
 172        bpf_slow_path_common(1)
 173        jr      $r_ra
 174         move   $r_A, $r_s0
 175
 176        END(bpf_slow_path_byte)
 177
 178/*
 179 * Negative entry points
 180 */
 181        .macro bpf_is_end_of_data
 182        li      t0, SKF_LL_OFF
 183        /* Reading link layer data? */
 184        slt     t1, offset, t0
 185        bgtz    t1, fault
 186        /* Be careful what follows in DS. */
 187        .endm
 188/*
 189 * call skb_copy_bits:
 190 * (prototype in linux/filter.h)
 191 *
 192 * void *bpf_internal_load_pointer_neg_helper(const struct sk_buff *skb,
 193 *                                            int k, unsigned int size)
 194 *
 195 * see above (bpf_slow_path_common) for ABI restrictions
 196 */
 197#define bpf_negative_common(SIZE)                                       \
 198        PTR_ADDIU       $r_sp, $r_sp, -(6 * SZREG);                     \
 199        PTR_LA          t0, bpf_internal_load_pointer_neg_helper;       \
 200        PTR_S           $r_ra, (5 * SZREG)($r_sp);                      \
 201        jalr            t0;                                             \
 202         li             a2, SIZE;                                       \
 203        PTR_L           $r_ra, (5 * SZREG)($r_sp);                      \
 204        /* Check return pointer */                                      \
 205        beqz            v0, fault;                                      \
 206         PTR_ADDIU      $r_sp, $r_sp, 6 * SZREG;                        \
 207        /* Preserve our pointer */                                      \
 208        move            $r_s0, v0;                                      \
 209        /* Set return value */                                          \
 210        move            $r_ret, zero;                                   \
 211
 212bpf_slow_path_word_neg:
 213        bpf_is_end_of_data
 214NESTED(sk_load_word_negative, (6 * SZREG), $r_sp)
 215        bpf_negative_common(4)
 216        jr      $r_ra
 217         lw     $r_A, 0($r_s0)
 218        END(sk_load_word_negative)
 219
 220bpf_slow_path_half_neg:
 221        bpf_is_end_of_data
 222NESTED(sk_load_half_negative, (6 * SZREG), $r_sp)
 223        bpf_negative_common(2)
 224        jr      $r_ra
 225         lhu    $r_A, 0($r_s0)
 226        END(sk_load_half_negative)
 227
 228bpf_slow_path_byte_neg:
 229        bpf_is_end_of_data
 230NESTED(sk_load_byte_negative, (6 * SZREG), $r_sp)
 231        bpf_negative_common(1)
 232        jr      $r_ra
 233         lbu    $r_A, 0($r_s0)
 234        END(sk_load_byte_negative)
 235
 236fault:
 237        jr      $r_ra
 238         addiu $r_ret, zero, 1
 239