Subject: Re: [PATCH v8 4/9] mm: introduce memfd_secret system call to create "secret" memory areas

From: Mike Rapoport <[email-masked]>
Date: Sun, 15 Nov 2020 10:53:07 +0200

On Fri, Nov 13, 2020 at 01:58:48PM +0000, Matthew Wilcox wrote:
> On Tue, Nov 10, 2020 at 05:14:39PM +0200, Mike Rapoport wrote:
> > +static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> > +{
> > +	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> > +	struct inode *inode = file_inode(vmf->vma->vm_file);
> > +	pgoff_t offset = vmf->pgoff;
> > +	unsigned long addr;
> > +	struct page *page;
> > +	int ret = 0;
> > +
> > +	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
> > +		return vmf_error(-EINVAL);
> > +
> > +	page = find_get_entry(mapping, offset);
> 
> Why did you decide to use find_get_entry() here?  You don't handle
> swap or shadow entries.

Right, I've missed that. 

> > +	if (!page) {
> > +		page = secretmem_alloc_page(vmf->gfp_mask);
> > +		if (!page)
> > +			return vmf_error(-EINVAL);
> 
> Why is this EINVAL and not ENOMEM?

Ah, I was annoyed by OOMs I got when I simulated various allocation
failures, so I changed it to get SIGBUS instead and than forgot to restore.
Will fix.

> > +		ret = add_to_page_cache(page, mapping, offset, vmf->gfp_mask);
> > +		if (unlikely(ret))
> > +			goto err_put_page;
> > +
> > +		ret = set_direct_map_invalid_noflush(page, 1);
> > +		if (ret)
> > +			goto err_del_page_cache;
> > +
> > +		addr = (unsigned long)page_address(page);
> > +		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> > +
> > +		__SetPageUptodate(page);
> > +
> > +		ret = VM_FAULT_LOCKED;
> > +	}
> > +
> > +	vmf->page = page;
> > +	return ret;
> 
> Does sparse not warn you about this abuse of vm_fault_t?  Separate out
> 'ret' and 'err'.
 
Will fix.

> Andrew, please fold in this fix.  I suspect Mike will want to fix
> the other things I mention above.
> 
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index 3dfdbd85ba00..09ca27f21661 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -172,7 +172,7 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
>  	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
>  		return vmf_error(-EINVAL);
>  
> -	page = find_get_entry(mapping, offset);
> +	page = find_get_page(mapping, offset);
>  	if (!page) {
>  		page = secretmem_alloc_page(ctx, vmf->gfp_mask);
>  		if (!page)

-- 
Sincerely yours,
Mike.

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