netdev - Re: [PATCH/RFC bpf-next 03/16] bpf: split read liveness into REG_LIVE_READ64 and REG_LIVE

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Message-ID: <CAG48ez0inUUF3wZw5P6o35T3CKQ=CEue1vo-H-dSLDKKo2OHow@mail.gmail.com>
Date:   Tue, 26 Mar 2019 21:21:46 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Jiong Wang <jiong.wang@...ronome.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>, bpf@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com
Subject: Re: [PATCH/RFC bpf-next 03/16] bpf: split read liveness into
 REG_LIVE_READ64 and REG_LIVE_READ32

On Tue, Mar 26, 2019 at 7:06 PM Jiong Wang <jiong.wang@...ronome.com> wrote:
>
> In previous patch, we have split register arg type for sub-register read,
> but haven't touch read liveness.
>
> This patch further split read liveness into REG_LIVE_READ64 and
> REG_LIVE_READ32. Liveness propagation code are updated accordingly.
>
> After this split, customized actions could be defined when propagating full
> register read (REG_LIVE_READ64) or sub-register read (REG_LIVE_READ32).
>
> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
[...]
> @@ -1374,7 +1374,8 @@ static int check_stack_read(struct bpf_verifier_env *env,
>                         return -EACCES;
>                 }
>                 mark_reg_read(env, &reg_state->stack[spi].spilled_ptr,
> -                             reg_state->stack[spi].spilled_ptr.parent);
> +                             reg_state->stack[spi].spilled_ptr.parent,
> +                             size == BPF_REG_SIZE);

Isn't it possible to use a 4-byte read on the upper half of an 8-byte
stack slot?

>                 if (value_regno >= 0) {
>                         if (zeros == size) {
>                                 /* any size read into register is zero extended,
> @@ -2220,7 +2221,8 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
>                  * the whole slot to be marked as 'read'
>                  */
>                 mark_reg_read(env, &state->stack[spi].spilled_ptr,
> -                             state->stack[spi].spilled_ptr.parent);
> +                             state->stack[spi].spilled_ptr.parent,
> +                             access_size == BPF_REG_SIZE);

Same thing as above.

>         }
>         return update_stack_depth(env, state, off);
>  }
[...]