Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220908170133.1159747-1-abrestic@rivosinc.com>
In-Reply-To: <20220908170133.1159747-1-abrestic@rivosinc.com>
From:   SS JieJi <c141028@gmail.com>
Date:   Fri, 9 Sep 2022 01:21:18 +0800
Message-ID: <CANaf2scedFxwDwBYNwk-9Y_p4O7Sc62FFjZPptdZeAs4H4JGiQ@mail.gmail.com>
Subject: Re: [PATCH] riscv: Allow PROT_WRITE-only mmap()
To:     Andrew Bresticker <abrestic@rivosinc.com>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Atish Patra <atishp@atishpatra.org>,
        Celeste Liu <coelacanthus@outlook.com>,
        dram <dramforever@live.com>, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

> is unnecessary since RISC-V defines its protection_map such that PROT_WRITE
> maps to the same PTE permissions as PROT_WRITE|PROT_READ, and it is
> inconsistent with other architectures that don't support write-only PTEs,
> creating a potential software portability issue.

I don't believe that the check is unnecessary. The missing check is
discovered in realworld scenario, while we are fixing libaio's test
failure on RISC-V [1]. A minimum reproducible example is uploaded to
https://fars.ee/1sPb, showing *inconsistent* read results on -r- pages
before/after a write attempt performed by the kernel.

[1]: https://pagure.io/libaio/blob/1b18bfafc6a2f7b9fa2c6be77a95afed8b7be448/f/harness/cases/5.t

> -       if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
> -               return -EINVAL;
> -

Just to mention, this revert patch is removing the check of exec
without read (--x), too.