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([2a01:e0a:e17:9700:16d2:7456:6634:9626]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38dc3a10fffsm13606012f8f.12.2025.02.11.02.31.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 02:31:28 -0800 (PST) Message-ID: Date: Tue, 11 Feb 2025 11:31:28 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 14/15] RISC-V: KVM: add support for FWFT SBI extension To: Deepak Gupta Cc: Paul Walmsley , Palmer Dabbelt , Anup Patel , Atish Patra , Shuah Khan , Jonathan Corbet , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, Samuel Holland References: <20250210213549.1867704-1-cleger@rivosinc.com> <20250210213549.1867704-15-cleger@rivosinc.com> Content-Language: en-US From: =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/02/2025 06:43, Deepak Gupta wrote: >> +static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long >> feature, >> +                unsigned long *value) >> +{ >> +    int ret; >> +    struct kvm_sbi_fwft_config *conf; >> + >> +    ret = kvm_fwft_get_feature(vcpu, feature, &conf); >> +    if (ret) >> +        return ret; >> + >> +    return conf->feature->get(vcpu, conf, value); >> +} >> + >> +static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct >> kvm_run *run, >> +                    struct kvm_vcpu_sbi_return *retdata) >> +{ >> +    int ret = 0; >> +    struct kvm_cpu_context *cp = &vcpu->arch.guest_context; >> +    unsigned long funcid = cp->a6; >> + >> +    switch (funcid) { >> +    case SBI_EXT_FWFT_SET: >> +        ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2); >> +        break; >> +    case SBI_EXT_FWFT_GET: >> +        ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val); >> +        break; >> +    default: >> +        ret = SBI_ERR_NOT_SUPPORTED; >> +        break; >> +    } >> + >> +    retdata->err_val = ret; >> + >> +    return 0; >> +} >> + >> +static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu) >> +{ >> +    struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu); >> +    const struct kvm_sbi_fwft_feature *feature; >> +    struct kvm_sbi_fwft_config *conf; >> +    int i; >> + >> +    fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct >> kvm_sbi_fwft_config), >> +                GFP_KERNEL); > nit: > > I understand that in next patch you grow the static array`features`. But > in this patch > `ARRAY_SIZE(features)` evaluates to 0, thus kcalloc will be returning a > pointer > to some slab block (IIRC, kcalloc will not return NULL if size > eventually evals to 0) > > This probably won't result in some bad stuff. But still there is a > pointer in > fwft->configs which is pointing to some random stuff if `features` turns > out to be > empty. > > Let me know if I got that right or missing something. So I actually searched into the kmalloc code to see what hapopens with a zero size allocation and it actually return ZERO_SIZE_PTR: /* * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. * * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault. * * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can. * Both make kfree a no-op. */ Which seems like it's not really random and will fault if accessed. I think that's enough for that commit (which will be bisectable if needed then). Clément