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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/isa-rev.h>
15#include <asm/regdef.h>
16#include "bpf_jit.h"
17
18/* ABI
19 *
20 * r_skb_hl skb header length
21 * r_skb_data skb data
22 * r_off(a1) offset register
23 * r_A BPF register A
24 * r_X PF register X
25 * r_skb(a0) *skb
26 * r_M *scratch memory
27 * r_skb_le skb length
28 * r_s0 Scratch register 0
29 * r_s1 Scratch register 1
30 *
31 * On entry:
32 * a0: *skb
33 * a1: offset (imm or imm + X)
34 *
35 * All non-BPF-ABI registers are free for use. On return, we only
36 * care about r_ret. The BPF-ABI registers are assumed to remain
37 * unmodified during the entire filter operation.
38 */
39
40#define skb a0
41#define offset a1
42#define SKF_LL_OFF (-0x200000) /* Can't include linux/filter.h in assembly */
43
44 /* We know better :) so prevent assembler reordering etc */
45 .set noreorder
46
47#define is_offset_negative(TYPE) \
48 /* If offset is negative we have more work to do */ \
49 slti t0, offset, 0; \
50 bgtz t0, bpf_slow_path_##TYPE##_neg; \
51 /* Be careful what follows in DS. */
52
53#define is_offset_in_header(SIZE, TYPE) \
54 /* Reading from header? */ \
55 addiu $r_s0, $r_skb_hl, -SIZE; \
56 slt t0, $r_s0, offset; \
57 bgtz t0, bpf_slow_path_##TYPE; \
58
59LEAF(sk_load_word)
60 is_offset_negative(word)
61FEXPORT(sk_load_word_positive)
62 is_offset_in_header(4, word)
63 /* Offset within header boundaries */
64 PTR_ADDU t1, $r_skb_data, offset
65 .set reorder
66 lw $r_A, 0(t1)
67 .set noreorder
68#ifdef CONFIG_CPU_LITTLE_ENDIAN
69# if MIPS_ISA_REV >= 2
70 wsbh t0, $r_A
71 rotr $r_A, t0, 16
72# else
73 sll t0, $r_A, 24
74 srl t1, $r_A, 24
75 srl t2, $r_A, 8
76 or t0, t0, t1
77 andi t2, t2, 0xff00
78 andi t1, $r_A, 0xff00
79 or t0, t0, t2
80 sll t1, t1, 8
81 or $r_A, t0, t1
82# endif
83#endif
84 jr $r_ra
85 move $r_ret, zero
86 END(sk_load_word)
87
88LEAF(sk_load_half)
89 is_offset_negative(half)
90FEXPORT(sk_load_half_positive)
91 is_offset_in_header(2, half)
92 /* Offset within header boundaries */
93 PTR_ADDU t1, $r_skb_data, offset
94 lhu $r_A, 0(t1)
95#ifdef CONFIG_CPU_LITTLE_ENDIAN
96# if MIPS_ISA_REV >= 2
97 wsbh $r_A, $r_A
98# else
99 sll t0, $r_A, 8
100 srl t1, $r_A, 8
101 andi t0, t0, 0xff00
102 or $r_A, t0, t1
103# endif
104#endif
105 jr $r_ra
106 move $r_ret, zero
107 END(sk_load_half)
108
109LEAF(sk_load_byte)
110 is_offset_negative(byte)
111FEXPORT(sk_load_byte_positive)
112 is_offset_in_header(1, byte)
113 /* Offset within header boundaries */
114 PTR_ADDU t1, $r_skb_data, offset
115 lbu $r_A, 0(t1)
116 jr $r_ra
117 move $r_ret, zero
118 END(sk_load_byte)
119
120/*
121 * call skb_copy_bits:
122 * (prototype in linux/skbuff.h)
123 *
124 * int skb_copy_bits(sk_buff *skb, int offset, void *to, int len)
125 *
126 * o32 mandates we leave 4 spaces for argument registers in case
127 * the callee needs to use them. Even though we don't care about
128 * the argument registers ourselves, we need to allocate that space
129 * to remain ABI compliant since the callee may want to use that space.
130 * We also allocate 2 more spaces for $r_ra and our return register (*to).
131 *
132 * n64 is a bit different. The *caller* will allocate the space to preserve
133 * the arguments. So in 64-bit kernels, we allocate the 4-arg space for no
134 * good reason but it does not matter that much really.
135 *
136 * (void *to) is returned in r_s0
137 *
138 */
139#ifdef CONFIG_CPU_LITTLE_ENDIAN
140#define DS_OFFSET(SIZE) (4 * SZREG)
141#else
142#define DS_OFFSET(SIZE) ((4 * SZREG) + (4 - SIZE))
143#endif
144#define bpf_slow_path_common(SIZE) \
145 /* Quick check. Are we within reasonable boundaries? */ \
146 LONG_ADDIU $r_s1, $r_skb_len, -SIZE; \
147 sltu $r_s0, offset, $r_s1; \
148 beqz $r_s0, fault; \
149 /* Load 4th argument in DS */ \
150 LONG_ADDIU a3, zero, SIZE; \
151 PTR_ADDIU $r_sp, $r_sp, -(6 * SZREG); \
152 PTR_LA t0, skb_copy_bits; \
153 PTR_S $r_ra, (5 * SZREG)($r_sp); \
154 /* Assign low slot to a2 */ \
155 PTR_ADDIU a2, $r_sp, DS_OFFSET(SIZE); \
156 jalr t0; \
157 /* Reset our destination slot (DS but it's ok) */ \
158 INT_S zero, (4 * SZREG)($r_sp); \
159 /* \
160 * skb_copy_bits returns 0 on success and -EFAULT \
161 * on error. Our data live in a2. Do not bother with \
162 * our data if an error has been returned. \
163 */ \
164 /* Restore our frame */ \
165 PTR_L $r_ra, (5 * SZREG)($r_sp); \
166 INT_L $r_s0, (4 * SZREG)($r_sp); \
167 bltz v0, fault; \
168 PTR_ADDIU $r_sp, $r_sp, 6 * SZREG; \
169 move $r_ret, zero; \
170
171NESTED(bpf_slow_path_word, (6 * SZREG), $r_sp)
172 bpf_slow_path_common(4)
173#ifdef CONFIG_CPU_LITTLE_ENDIAN
174# if MIPS_ISA_REV >= 2
175 wsbh t0, $r_s0
176 jr $r_ra
177 rotr $r_A, t0, 16
178# else
179 sll t0, $r_s0, 24
180 srl t1, $r_s0, 24
181 srl t2, $r_s0, 8
182 or t0, t0, t1
183 andi t2, t2, 0xff00
184 andi t1, $r_s0, 0xff00
185 or t0, t0, t2
186 sll t1, t1, 8
187 jr $r_ra
188 or $r_A, t0, t1
189# endif
190#else
191 jr $r_ra
192 move $r_A, $r_s0
193#endif
194
195 END(bpf_slow_path_word)
196
197NESTED(bpf_slow_path_half, (6 * SZREG), $r_sp)
198 bpf_slow_path_common(2)
199#ifdef CONFIG_CPU_LITTLE_ENDIAN
200# if MIPS_ISA_REV >= 2
201 jr $r_ra
202 wsbh $r_A, $r_s0
203# else
204 sll t0, $r_s0, 8
205 andi t1, $r_s0, 0xff00
206 andi t0, t0, 0xff00
207 srl t1, t1, 8
208 jr $r_ra
209 or $r_A, t0, t1
210# endif
211#else
212 jr $r_ra
213 move $r_A, $r_s0
214#endif
215
216 END(bpf_slow_path_half)
217
218NESTED(bpf_slow_path_byte, (6 * SZREG), $r_sp)
219 bpf_slow_path_common(1)
220 jr $r_ra
221 move $r_A, $r_s0
222
223 END(bpf_slow_path_byte)
224
225/*
226 * Negative entry points
227 */
228 .macro bpf_is_end_of_data
229 li t0, SKF_LL_OFF
230 /* Reading link layer data? */
231 slt t1, offset, t0
232 bgtz t1, fault
233 /* Be careful what follows in DS. */
234 .endm
235/*
236 * call skb_copy_bits:
237 * (prototype in linux/filter.h)
238 *
239 * void *bpf_internal_load_pointer_neg_helper(const struct sk_buff *skb,
240 * int k, unsigned int size)
241 *
242 * see above (bpf_slow_path_common) for ABI restrictions
243 */
244#define bpf_negative_common(SIZE) \
245 PTR_ADDIU $r_sp, $r_sp, -(6 * SZREG); \
246 PTR_LA t0, bpf_internal_load_pointer_neg_helper; \
247 PTR_S $r_ra, (5 * SZREG)($r_sp); \
248 jalr t0; \
249 li a2, SIZE; \
250 PTR_L $r_ra, (5 * SZREG)($r_sp); \
251 /* Check return pointer */ \
252 beqz v0, fault; \
253 PTR_ADDIU $r_sp, $r_sp, 6 * SZREG; \
254 /* Preserve our pointer */ \
255 move $r_s0, v0; \
256 /* Set return value */ \
257 move $r_ret, zero; \
258
259bpf_slow_path_word_neg:
260 bpf_is_end_of_data
261NESTED(sk_load_word_negative, (6 * SZREG), $r_sp)
262 bpf_negative_common(4)
263 jr $r_ra
264 lw $r_A, 0($r_s0)
265 END(sk_load_word_negative)
266
267bpf_slow_path_half_neg:
268 bpf_is_end_of_data
269NESTED(sk_load_half_negative, (6 * SZREG), $r_sp)
270 bpf_negative_common(2)
271 jr $r_ra
272 lhu $r_A, 0($r_s0)
273 END(sk_load_half_negative)
274
275bpf_slow_path_byte_neg:
276 bpf_is_end_of_data
277NESTED(sk_load_byte_negative, (6 * SZREG), $r_sp)
278 bpf_negative_common(1)
279 jr $r_ra
280 lbu $r_A, 0($r_s0)
281 END(sk_load_byte_negative)
282
283fault:
284 jr $r_ra
285 addiu $r_ret, zero, 1