Re: [PATCH 02/17] prmem: write rare for static allocation

[Igor Stoppa]

On 26/10/2018 10:41, Peter Zijlstra wrote:
> On Wed, Oct 24, 2018 at 12:34:49AM +0300, Igor Stoppa wrote:
> > +static __always_inline
>
> That's far too large for inline.

The reason for it is that it's supposed to minimize the presence of 
gadgets that might be used in JOP attacks.
I am ready to stand corrected, if I'm wrong, but this is the reason why 
I did it.

Regarding the function being too large, yes, I would not normally choose 
it for inlining.

Actually, I would not normally use "__always_inline" and instead I would 
limit myself to plain "inline", at most.

> > +bool wr_memset(const void *dst, const int c, size_t n_bytes)
> > +{
> > +	size_t size;
> > +	unsigned long flags;
> > +	uintptr_t d = (uintptr_t)dst;
> > +
> > +	if (WARN(!__is_wr_after_init(dst, n_bytes), WR_ERR_RANGE_MSG))
> > +		return false;
> > +	while (n_bytes) {
> > +		struct page *page;
> > +		uintptr_t base;
> > +		uintptr_t offset;
> > +		uintptr_t offset_complement;
> > +
> > +		local_irq_save(flags);
> > +		page = virt_to_page(d);
> > +		offset = d & ~PAGE_MASK;
> > +		offset_complement = PAGE_SIZE - offset;
> > +		size = min(n_bytes, offset_complement);
> > +		base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> > +		if (WARN(!base, WR_ERR_PAGE_MSG)) {
> > +			local_irq_restore(flags);
> > +			return false;
> > +		}
> > +		memset((void *)(base + offset), c, size);
> > +		vunmap((void *)base);
>
> BUG

yes, somehow I managed to drop this debug configuration from the debug 
builds I made.

[...]

> Also, I see an amount of duplication here that shows you're not nearly
> lazy enough.

I did notice a certain amount of duplication, but I didn't know how to 
exploit it.

--
igor