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/*
* bpf_jib_asm.S: Packet/header access helper functions for MIPS/MIPS64 BPF
* compiler.
*
* Copyright (C) 2015 Imagination Technologies Ltd.
* Author: Markos Chandras <markos.chandras@imgtec.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; version 2 of the License.
*/
#include <asm/asm.h>
#include <asm/regdef.h>
#include "bpf_jit.h"
/* ABI
*
* r_skb_hl skb header length
* r_skb_data skb data
* r_off(a1) offset register
* r_A BPF register A
* r_X PF register X
* r_skb(a0) *skb
* r_M *scratch memory
* r_skb_le skb length
* r_s0 Scratch register 0
* r_s1 Scratch register 1
*
* On entry:
* a0: *skb
* a1: offset (imm or imm + X)
*
* All non-BPF-ABI registers are free for use. On return, we only
* care about r_ret. The BPF-ABI registers are assumed to remain
* unmodified during the entire filter operation.
*/
#define skb a0
#define offset a1
#define SKF_LL_OFF (-0x200000) /* Can't include linux/filter.h in assembly */
/* We know better :) so prevent assembler reordering etc */
.set noreorder
#define is_offset_negative(TYPE) \
/* If offset is negative we have more work to do */ \
slti t0, offset, 0; \
bgtz t0, bpf_slow_path_##TYPE##_neg; \
/* Be careful what follows in DS. */
#define is_offset_in_header(SIZE, TYPE) \
/* Reading from header? */ \
addiu $r_s0, $r_skb_hl, -SIZE; \
slt t0, $r_s0, offset; \
bgtz t0, bpf_slow_path_##TYPE; \
LEAF(sk_load_word)
is_offset_negative(word)
.globl sk_load_word_positive
sk_load_word_positive:
is_offset_in_header(4, word)
/* Offset within header boundaries */
PTR_ADDU t1, $r_skb_data, offset
lw $r_A, 0(t1)
#ifdef CONFIG_CPU_LITTLE_ENDIAN
wsbh t0, $r_A
rotr $r_A, t0, 16
#endif
jr $r_ra
move $r_ret, zero
END(sk_load_word)
LEAF(sk_load_half)
is_offset_negative(half)
.globl sk_load_half_positive
sk_load_half_positive:
is_offset_in_header(2, half)
/* Offset within header boundaries */
PTR_ADDU t1, $r_skb_data, offset
lh $r_A, 0(t1)
#ifdef CONFIG_CPU_LITTLE_ENDIAN
wsbh t0, $r_A
seh $r_A, t0
#endif
jr $r_ra
move $r_ret, zero
END(sk_load_half)
LEAF(sk_load_byte)
is_offset_negative(byte)
.globl sk_load_byte_positive
sk_load_byte_positive:
is_offset_in_header(1, byte)
/* Offset within header boundaries */
PTR_ADDU t1, $r_skb_data, offset
lb $r_A, 0(t1)
jr $r_ra
move $r_ret, zero
END(sk_load_byte)
/*
* call skb_copy_bits:
* (prototype in linux/skbuff.h)
*
* int skb_copy_bits(sk_buff *skb, int offset, void *to, int len)
*
* o32 mandates we leave 4 spaces for argument registers in case
* the callee needs to use them. Even though we don't care about
* the argument registers ourselves, we need to allocate that space
* to remain ABI compliant since the callee may want to use that space.
* We also allocate 2 more spaces for $r_ra and our return register (*to).
*
* n64 is a bit different. The *caller* will allocate the space to preserve
* the arguments. So in 64-bit kernels, we allocate the 4-arg space for no
* good reason but it does not matter that much really.
*
* (void *to) is returned in r_s0
*
*/
#define bpf_slow_path_common(SIZE) \
/* Quick check. Are we within reasonable boundaries? */ \
LONG_ADDIU $r_s1, $r_skb_len, -SIZE; \
sltu $r_s0, offset, $r_s1; \
beqz $r_s0, fault; \
/* Load 4th argument in DS */ \
LONG_ADDIU a3, zero, SIZE; \
PTR_ADDIU $r_sp, $r_sp, -(6 * SZREG); \
PTR_LA t0, skb_copy_bits; \
PTR_S $r_ra, (5 * SZREG)($r_sp); \
/* Assign low slot to a2 */ \
move a2, $r_sp; \
jalr t0; \
/* Reset our destination slot (DS but it's ok) */ \
INT_S zero, (4 * SZREG)($r_sp); \
/* \
* skb_copy_bits returns 0 on success and -EFAULT \
* on error. Our data live in a2. Do not bother with \
* our data if an error has been returned. \
*/ \
/* Restore our frame */ \
PTR_L $r_ra, (5 * SZREG)($r_sp); \
INT_L $r_s0, (4 * SZREG)($r_sp); \
bltz v0, fault; \
PTR_ADDIU $r_sp, $r_sp, 6 * SZREG; \
move $r_ret, zero; \
NESTED(bpf_slow_path_word, (6 * SZREG), $r_sp)
bpf_slow_path_common(4)
#ifdef CONFIG_CPU_LITTLE_ENDIAN
wsbh t0, $r_s0
jr $r_ra
rotr $r_A, t0, 16
#endif
jr $r_ra
move $r_A, $r_s0
END(bpf_slow_path_word)
NESTED(bpf_slow_path_half, (6 * SZREG), $r_sp)
bpf_slow_path_common(2)
#ifdef CONFIG_CPU_LITTLE_ENDIAN
jr $r_ra
wsbh $r_A, $r_s0
#endif
jr $r_ra
move $r_A, $r_s0
END(bpf_slow_path_half)
NESTED(bpf_slow_path_byte, (6 * SZREG), $r_sp)
bpf_slow_path_common(1)
jr $r_ra
move $r_A, $r_s0
END(bpf_slow_path_byte)
/*
* Negative entry points
*/
.macro bpf_is_end_of_data
li t0, SKF_LL_OFF
/* Reading link layer data? */
slt t1, offset, t0
bgtz t1, fault
/* Be careful what follows in DS. */
.endm
/*
* call skb_copy_bits:
* (prototype in linux/filter.h)
*
* void *bpf_internal_load_pointer_neg_helper(const struct sk_buff *skb,
* int k, unsigned int size)
*
* see above (bpf_slow_path_common) for ABI restrictions
*/
#define bpf_negative_common(SIZE) \
PTR_ADDIU $r_sp, $r_sp, -(6 * SZREG); \
PTR_LA t0, bpf_internal_load_pointer_neg_helper; \
PTR_S $r_ra, (5 * SZREG)($r_sp); \
jalr t0; \
li a2, SIZE; \
PTR_L $r_ra, (5 * SZREG)($r_sp); \
/* Check return pointer */ \
beqz v0, fault; \
PTR_ADDIU $r_sp, $r_sp, 6 * SZREG; \
/* Preserve our pointer */ \
move $r_s0, v0; \
/* Set return value */ \
move $r_ret, zero; \
bpf_slow_path_word_neg:
bpf_is_end_of_data
NESTED(sk_load_word_negative, (6 * SZREG), $r_sp)
bpf_negative_common(4)
jr $r_ra
lw $r_A, 0($r_s0)
END(sk_load_word_negative)
bpf_slow_path_half_neg:
bpf_is_end_of_data
NESTED(sk_load_half_negative, (6 * SZREG), $r_sp)
bpf_negative_common(2)
jr $r_ra
lhu $r_A, 0($r_s0)
END(sk_load_half_negative)
bpf_slow_path_byte_neg:
bpf_is_end_of_data
NESTED(sk_load_byte_negative, (6 * SZREG), $r_sp)
bpf_negative_common(1)
jr $r_ra
lbu $r_A, 0($r_s0)
END(sk_load_byte_negative)
fault:
jr $r_ra
addiu $r_ret, zero, 1
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