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

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Date:   Wed, 10 Mar 2021 17:00:35 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-sgx@...r.kernel.org, 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 Wed, Mar 03, 2021 at 08:56:52AM -0800, Dave Hansen wrote:
> 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?

In sgx_setup_epc_section():


	section->pages = vmalloc(nr_pages * sizeof(struct sgx_epc_page));
	if (!section->pages) {
		memunmap(section->virt_addr);
		return false;
	}

I.e. this rollback does not happen without this fix applied:

	for (i = 0; i < sgx_nr_epc_sections; i++) {
		vfree(sgx_epc_sections[i].pages);
		memunmap(sgx_epc_sections[i].virt_addr);
	}

/Jarkko