linux-kernel - Re: [RFC PATCH v2 3/5] x86/sgx: Enforce noexec filesystem restriction for enclaves

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Message-ID: <20190610160005.GC3752@linux.intel.com>
Date:   Mon, 10 Jun 2019 19:00:18 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Cedric Xing <cedric.xing@...el.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, nhorman@...hat.com,
        npmccallum@...hat.com, Serge Ayoun <serge.ayoun@...el.com>,
        Shay Katz-zamir <shay.katz-zamir@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kai Svahn <kai.svahn@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        Kai Huang <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        William Roberts <william.c.roberts@...el.com>,
        Philip Tricca <philip.b.tricca@...el.com>
Subject: Re: [RFC PATCH v2 3/5] x86/sgx: Enforce noexec filesystem
 restriction for enclaves

On Wed, Jun 05, 2019 at 07:11:43PM -0700, Sean Christopherson wrote:
> +		goto out;
> +	}
> +
> +	/*
> +	 * Query VM_MAYEXEC as an indirect path_noexec() check (see do_mmap()),
> +	 * but with some future proofing against other cases that may deny
> +	 * execute permissions.
> +	 */
> +	if (!(vma->vm_flags & VM_MAYEXEC)) {
> +		ret = -EACCES;
> +		goto out;
> +	}
> +
> +	if (copy_from_user(dst, (void __user *)src, PAGE_SIZE))
> +		ret = -EFAULT;
> +	else
> +		ret = 0;
> +
> +out:
> +	up_read(&current->mm->mmap_sem);
> +
> +	return ret;
> +}

I would suggest to express the above instead like this for clarity
and consistency:

		goto err_map_sem;
	}

	/* Query VM_MAYEXEC as an indirect path_noexec() check
	 * (see do_mmap()).
	 */
	if (!(vma->vm_flags & VM_MAYEXEC)) {
		ret = -EACCES;
		goto err_mmap_sem;
	}

	if (copy_from_user(dst, (void __user *)src, PAGE_SIZE)) {
		ret = -EFAULT;
		goto err_mmap_sem;
	}

	return 0;

err_mmap_sem:
	up_read(&current->mm->mmap_sem);
	return ret;
}

The comment about future proofing is unnecessary.

/Jarkk