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bpf: Support new signed div/mod instructions.

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Add interpreter/jit support for new signed div/mod insns.
The new signed div/mod instructions are encoded with
unsigned div/mod instructions plus insn->off == 1.
Also add basic verifier support to ensure new insns get
accepted.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011219.3714605-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2023-07-27 18:12:19 -07:00 committed by Alexei Starovoitov
parent 0845c3db7b
commit ec0e2da95f
3 changed files with 117 additions and 26 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

11
arch/x86/net/bpf_jit_comp.c
View file

@ -1194,6 +1194,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
/* mov rax, dst_reg */
emit_mov_reg(&prog, is64, BPF_REG_0, dst_reg);
if (insn->off == 0) {
/*
* xor edx, edx
* equivalent to 'xor rdx, rdx', but one byte less
@ -1203,6 +1204,16 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
/* div src_reg */
maybe_emit_1mod(&prog, src_reg, is64);
EMIT2(0xF7, add_1reg(0xF0, src_reg));
} else {
if (BPF_CLASS(insn->code) == BPF_ALU)
EMIT1(0x99); /* cdq */
else
EMIT2(0x48, 0x99); /* cqo */
/* idiv src_reg */
maybe_emit_1mod(&prog, src_reg, is64);
EMIT2(0xF7, add_1reg(0xF8, src_reg));
}
if (BPF_OP(insn->code) == BPF_MOD &&
dst_reg != BPF_REG_3)

78
kernel/bpf/core.c
View file

@ -1792,36 +1792,114 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
(*(s64 *) &DST) >>= IMM;
CONT;
ALU64_MOD_X:
switch (OFF) {
case 0:
div64_u64_rem(DST, SRC, &AX);
DST = AX;
break;
case 1:
AX = div64_s64(DST, SRC);
DST = DST - AX * SRC;
break;
}
CONT;
ALU_MOD_X:
switch (OFF) {
case 0:
AX = (u32) DST;
DST = do_div(AX, (u32) SRC);
break;
case 1:
AX = abs((s32)DST);
AX = do_div(AX, abs((s32)SRC));
if ((s32)DST < 0)
DST = (u32)-AX;
else
DST = (u32)AX;
break;
}
CONT;
ALU64_MOD_K:
switch (OFF) {
case 0:
div64_u64_rem(DST, IMM, &AX);
DST = AX;
break;
case 1:
AX = div64_s64(DST, IMM);
DST = DST - AX * IMM;
break;
}
CONT;
ALU_MOD_K:
switch (OFF) {
case 0:
AX = (u32) DST;
DST = do_div(AX, (u32) IMM);
break;
case 1:
AX = abs((s32)DST);
AX = do_div(AX, abs((s32)IMM));
if ((s32)DST < 0)
DST = (u32)-AX;
else
DST = (u32)AX;
break;
}
CONT;
ALU64_DIV_X:
switch (OFF) {
case 0:
DST = div64_u64(DST, SRC);
break;
case 1:
DST = div64_s64(DST, SRC);
break;
}
CONT;
ALU_DIV_X:
switch (OFF) {
case 0:
AX = (u32) DST;
do_div(AX, (u32) SRC);
DST = (u32) AX;
break;
case 1:
AX = abs((s32)DST);
do_div(AX, abs((s32)SRC));
if ((s32)DST < 0 == (s32)SRC < 0)
DST = (u32)AX;
else
DST = (u32)-AX;
break;
}
CONT;
ALU64_DIV_K:
switch (OFF) {
case 0:
DST = div64_u64(DST, IMM);
break;
case 1:
DST = div64_s64(DST, IMM);
break;
}
CONT;
ALU_DIV_K:
switch (OFF) {
case 0:
AX = (u32) DST;
do_div(AX, (u32) IMM);
DST = (u32) AX;
break;
case 1:
AX = abs((s32)DST);
do_div(AX, abs((s32)IMM));
if ((s32)DST < 0 == (s32)IMM < 0)
DST = (u32)AX;
else
DST = (u32)-AX;
break;
}
CONT;
ALU_END_TO_BE:
switch (IMM) {

6
kernel/bpf/verifier.c
View file

@ -13237,7 +13237,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
} else { /* all other ALU ops: and, sub, xor, add, ... */
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0 || insn->off != 0) {
if (insn->imm != 0 || insn->off > 1 ||
(insn->off == 1 && opcode != BPF_MOD && opcode != BPF_DIV)) {
verbose(env, "BPF_ALU uses reserved fields\n");
return -EINVAL;
}
@ -13246,7 +13247,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
if (err)
return err;
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
if (insn->src_reg != BPF_REG_0 || insn->off > 1 ||
(insn->off == 1 && opcode != BPF_MOD && opcode != BPF_DIV)) {
verbose(env, "BPF_ALU uses reserved fields\n");
return -EINVAL;
}