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bpf, x86: Fix signed 32-bit div/mod in the i386 JIT #12801

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bpf, x86: Fix signed 32-bit div/mod in the i386 JIT #12801

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23 changes: 16 additions & 7 deletions arch/x86/net/bpf_jit_comp32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -433,7 +433,8 @@ static inline void emit_ia32_to_be_r64(const u8 dst[], s32 val,
* dst = dst (div|mod) src
*/
static inline void emit_ia32_div_mod_r(const u8 op, const u8 dst, const u8 src,
bool dstk, bool sstk, u8 **pprog)
bool dstk, bool sstk, bool is_signed,
u8 **pprog)
{
u8 *prog = *pprog;
int cnt = 0;
Expand All @@ -454,10 +455,17 @@ static inline void emit_ia32_div_mod_r(const u8 op, const u8 dst, const u8 src,
/* mov eax,dst */
EMIT2(0x8B, add_2reg(0xC0, dst, IA32_EAX));

/* xor edx,edx */
EMIT2(0x31, add_2reg(0xC0, IA32_EDX, IA32_EDX));
/* div ecx */
EMIT2(0xF7, add_1reg(0xF0, IA32_ECX));
if (is_signed) {
/* cdq */
EMIT1(0x99);
/* idiv ecx */
EMIT2(0xF7, add_1reg(0xF8, IA32_ECX));
} else {
/* xor edx,edx */
EMIT2(0x31, add_2reg(0xC0, IA32_EDX, IA32_EDX));
/* div ecx */
EMIT2(0xF7, add_1reg(0xF0, IA32_ECX));
}

if (op == BPF_MOD) {
if (dstk)
Expand Down Expand Up @@ -1796,15 +1804,16 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
switch (BPF_SRC(code)) {
case BPF_X:
emit_ia32_div_mod_r(BPF_OP(code), dst_lo,
src_lo, dstk, sstk, &prog);
src_lo, dstk, sstk,
insn->off == 1, &prog);
break;
case BPF_K:
/* mov ecx,imm32*/
EMIT2_off32(0xC7, add_1reg(0xC0, IA32_ECX),
imm32);
emit_ia32_div_mod_r(BPF_OP(code), dst_lo,
IA32_ECX, dstk, false,
&prog);
insn->off == 1, &prog);
break;
}
if (!bpf_prog->aux->verifier_zext)
Expand Down
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