linux-kernel - Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx

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Message-ID: <57b33fb5-f961-5c81-72f1-ebf5e6af671c@intel.com>
Date:   Wed, 3 Mar 2021 08:56:52 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Serge Ayoun <serge.ayoun@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] x86/sgx: Fix a resource leak in sgx_init()

On 3/3/21 7:03 AM, Jarkko Sakkinen wrote:
> If sgx_page_cache_init() fails in the middle, a trivial return
> statement causes unused memory and virtual address space reserved for
> the EPC section, not freed. Fix this by using the same rollback, as
> when sgx_page_reclaimer_init() fails.
...
> @@ -708,8 +708,10 @@ static int __init sgx_init(void)
>  	if (!cpu_feature_enabled(X86_FEATURE_SGX))
>  		return -ENODEV;
>  
> -	if (!sgx_page_cache_init())
> -		return -ENOMEM;
> +	if (!sgx_page_cache_init()) {
> +		ret = -ENOMEM;
> +		goto err_page_cache;
> +	}


Currently, the only way sgx_page_cache_init() can fail is in the case
that there are no sections:

        if (!sgx_nr_epc_sections) {
                pr_err("There are zero EPC sections.\n");
                return false;
        }

That only happened if all sgx_setup_epc_section() calls failed.
sgx_setup_epc_section() never both allocates memory with vmalloc for
section->pages *and* fails.  If sgx_setup_epc_section() has a successful
memremap() but a failed vmalloc(), it cleans up with memunmap().

In other words, I see how this _looks_ like a memory leak from
sgx_init(), but I don't see an actual leak in practice.

Am I missing something?