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