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