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bpf: preserve constant zero when doing partial register restore
Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from stack from slot that has register spilled into it and that register has a constant value zero, preserve that zero and mark spilled register as precise for that. This makes spilled const zero register and STACK_ZERO cases equivalent in their behavior. Acked-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20231205184248.1502704-7-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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1 changed files with 21 additions and 4 deletions
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@ -4767,22 +4767,39 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
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copy_register_state(&state->regs[dst_regno], reg);
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state->regs[dst_regno].subreg_def = subreg_def;
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} else {
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int spill_cnt = 0, zero_cnt = 0;
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for (i = 0; i < size; i++) {
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type = stype[(slot - i) % BPF_REG_SIZE];
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if (type == STACK_SPILL)
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if (type == STACK_SPILL) {
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spill_cnt++;
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continue;
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}
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if (type == STACK_MISC)
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continue;
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if (type == STACK_ZERO)
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if (type == STACK_ZERO) {
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zero_cnt++;
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continue;
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}
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if (type == STACK_INVALID && env->allow_uninit_stack)
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continue;
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verbose(env, "invalid read from stack off %d+%d size %d\n",
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off, i, size);
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return -EACCES;
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}
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mark_reg_unknown(env, state->regs, dst_regno);
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insn_flags = 0; /* not restoring original register state */
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if (spill_cnt == size &&
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tnum_is_const(reg->var_off) && reg->var_off.value == 0) {
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__mark_reg_const_zero(&state->regs[dst_regno]);
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/* this IS register fill, so keep insn_flags */
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} else if (zero_cnt == size) {
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/* similarly to mark_reg_stack_read(), preserve zeroes */
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__mark_reg_const_zero(&state->regs[dst_regno]);
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insn_flags = 0; /* not restoring original register state */
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} else {
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mark_reg_unknown(env, state->regs, dst_regno);
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insn_flags = 0; /* not restoring original register state */
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}
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}
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state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
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} else if (dst_regno >= 0) {
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