linux-kernel - Re: [PATCH 16/17] prmem: pratomic-long

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Date:   Thu, 25 Oct 2018 02:13:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        James Morris <jmorris@...ei.org>,
        Michal Hocko <mhocko@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, igor.stoppa@...wei.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/17] prmem: pratomic-long

On Wed, Oct 24, 2018 at 12:35:03AM +0300, Igor Stoppa wrote:
> +static __always_inline
> +bool __pratomic_long_op(bool inc, struct pratomic_long_t *l)
> +{
> +	struct page *page;
> +	uintptr_t base;
> +	uintptr_t offset;
> +	unsigned long flags;
> +	size_t size = sizeof(*l);
> +	bool is_virt = __is_wr_after_init(l, size);
> +
> +	if (WARN(!(is_virt || likely(__is_wr_pool(l, size))),
> +		 WR_ERR_RANGE_MSG))
> +		return false;
> +	local_irq_save(flags);
> +	if (is_virt)
> +		page = virt_to_page(l);
> +	else
> +		vmalloc_to_page(l);
> +	offset = (~PAGE_MASK) & (uintptr_t)l;
> +	base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> +	if (WARN(!base, WR_ERR_PAGE_MSG)) {
> +		local_irq_restore(flags);
> +		return false;
> +	}
> +	if (inc)
> +		atomic_long_inc((atomic_long_t *)(base + offset));
> +	else
> +		atomic_long_dec((atomic_long_t *)(base + offset));
> +	vunmap((void *)base);
> +	local_irq_restore(flags);
> +	return true;
> +
> +}

That's just hideously nasty.. and horribly broken.

We're not going to duplicate all these kernel interfaces wrapped in gunk
like that. Also, you _cannot_ call vunmap() with IRQs disabled. Clearly
you've never tested this with debug bits enabled.