linux-kernel - Re: [PATCH 4/4] iommu/vt-d: Do access checks before calling handle_mm

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Date:	Tue, 10 Nov 2015 15:52:26 +0100
From:	Joerg Roedel <jroedel@...e.de>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
	Oded Gabbay <oded.gabbay@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org
Subject: Re: [PATCH 4/4] iommu/vt-d: Do access checks before calling
 handle_mm_fault()

On Tue, Nov 10, 2015 at 02:45:56PM +0000, David Woodhouse wrote:
> On Tue, 2015-11-10 at 14:26 +0100, Joerg Roedel wrote:
> > +static bool access_error(struct vm_area_struct *vma, struct
> > page_req_dsc *req)
> > +{
> > +	return !((req->rd_req  && (vma->vm_flags & VM_READ))  ||
> > +		 (req->wr_req  && (vma->vm_flags & VM_WRITE)) ||
> > +		 (req->exe_req && (vma->vm_flags & VM_EXEC)));
> > +}
> > +
> 
> This is a TLB fill request from the device — can it not be asking for
> *all* of read, write and exec privs? And you allow it to succeed if any
> *one* of the permissions that it asks for is available?
> 
> Even if we don't see read+write in the same request, the VT-d spec does
> seem quite clear that we *will* see read+exec (§7.5.1.1 p7-17 of v2.3:
> 
> • Execute Requested: If the PASID Present, Read Requested and Execute
>   Requested fields are all 1, the request-with-PASID that encountered 
>   the recoverable fault that resulted in this page request, requires 
>   execute access to the page.

Okay, thanks for the clarification. The code above assumes that only one
of RWX is set. I'll update the patch to correctly check when multiple
bits are set.


	Joerg

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