On Tue, Mar 24, 2020 at 10:38:56AM -0700, John Fastabend wrote:
> -static void __reg_bound_offset32(struct bpf_reg_state *reg)
> +static void __reg_combine_32_into_64(struct bpf_reg_state *reg)
> {
> - u64 mask = 0xffffFFFF;
> - struct tnum range = tnum_range(reg->umin_value & mask,
> - reg->umax_value & mask);
> - struct tnum lo32 = tnum_cast(reg->var_off, 4);
> - struct tnum hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32);
> + /* special case when 64-bit register has upper 32-bit register
> + * zeroed. Typically happens after zext or <<32, >>32 sequence
> + * allowing us to use 32-bit bounds directly,
> + */
> + if (tnum_equals_const(tnum_clear_subreg(reg->var_off), 0)) {
> + reg->umin_value = reg->u32_min_value;
> + reg->umax_value = reg->u32_max_value;
> + reg->smin_value = reg->s32_min_value;
> + reg->smax_value = reg->s32_max_value;
Looks like above will not be correct for negative s32_min/max.
When upper 32-bit are cleared and we're processing jmp32
we cannot set smax_value to s32_max_value.
Consider if (w0 s< -5)
s32_max_value == -5
which is 0xfffffffb
but upper 32 are zeros so smax_value should be (u64)0xfffffffb
and not (s64)-5
We can be fancy and precise with this logic, but I would just use similar
approach from zext_32_to_64() where the following:
+ if (reg->s32_min_value > 0)
+ reg->smin_value = reg->s32_min_value;
+ else
+ reg->smin_value = 0;
+ if (reg->s32_max_value > 0)
+ reg->smax_value = reg->s32_max_value;
+ else
+ reg->smax_value = U32_MAX;
should work for this case too ?
> + if (BPF_SRC(insn->code) == BPF_K) {
> + pred = is_branch_taken(dst_reg, insn->imm, opcode, is_jmp32);
> + } else if (src_reg->type == SCALAR_VALUE && is_jmp32 && tnum_is_const(tnum_subreg(src_reg->var_off))) {
> + pred = is_branch_taken(dst_reg, tnum_subreg(src_reg->var_off).value, opcode, is_jmp32);
> + } else if (src_reg->type == SCALAR_VALUE && !is_jmp32 && tnum_is_const(src_reg->var_off)) {
> + pred = is_branch_taken(dst_reg, src_reg->var_off.value, opcode, is_jmp32);
> + }
pls wrap these lines. Way above normal.
The rest is awesome.
