Re: [PATCH v33 10/21] mm: Introduce vm_ops->may_mprotect()

From: Matthew Wilcox <willy@infradead.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	x86@kernel.org, linux-sgx@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Jethro Beekman <jethro@fortanix.com>,
	akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
	asapek@google.com, cedric.xing@intel.com,
	chenalexchen@google.com, conradparker@google.com,
	cyhanish@google.com, dave.hansen@intel.com,
	haitao.huang@intel.com, josh@joshtriplett.org,
	kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
	ludloff@google.com, luto@kernel.org, nhorman@redhat.com,
	npmccallum@redhat.com, puiterwijk@redhat.com,
	rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com,
	linux-mm@kvack.org
Subject: Re: [PATCH v33 10/21] mm: Introduce vm_ops->may_mprotect()
Date: Thu, 25 Jun 2020 18:30:50 +0100	[thread overview]
Message-ID: <20200625173050.GF7703@casper.infradead.org> (raw)
In-Reply-To: <20200625171416.GI20319@zn.tnic>

On Thu, Jun 25, 2020 at 07:14:16PM +0200, Borislav Petkov wrote:
> On Thu, Jun 18, 2020 at 01:08:32AM +0300, Jarkko Sakkinen wrote:
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> Something ate the Cc:s. Lemme add the mm list, akpm is already on Cc.
> 
> Leaving in the rest for mm folks.

Thanks!

> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index dc7b87310c10..be40b9c29327 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -542,6 +542,8 @@ struct vm_operations_struct {
> >  	void (*close)(struct vm_area_struct * area);
> >  	int (*split)(struct vm_area_struct * area, unsigned long addr);
> >  	int (*mremap)(struct vm_area_struct * area);
> > +	int (*may_mprotect)(struct vm_area_struct *vma, unsigned long start,
> > +			    unsigned long end, unsigned long prot);

This is unlike any other vm operation.  Every other one is a verb.

> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index ce8b8a5eacbb..f7731dc13ff0 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -603,13 +603,21 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
> >  			goto out;
> >  		}
> >  
> > +		tmp = vma->vm_end;
> > +		if (tmp > end)
> > +			tmp = end;
> > +
> > +		if (vma->vm_ops && vma->vm_ops->may_mprotect) {
> > +			error = vma->vm_ops->may_mprotect(vma, nstart, tmp,
> > +							  prot);
> > +			if (error)
> > +				goto out;
> > +		}
> > +
> >  		error = security_file_mprotect(vma, reqprot, prot);
> >  		if (error)
> >  			goto out;
> >  

I think the right way to do this is:

                error = security_file_mprotect(vma, reqprot, prot);
                if (error)
                        goto out;

                tmp = vma->vm_end;
                if (tmp > end)
                        tmp = end;
+		if (vma->vm_ops->mprotect)
+			error = vma->vm_ops->mprotect(vma, &prev, nstart, tmp,
+					newflags);
+		else
+			error = mprotect_fixup(vma, &prev, nstart, tmp,
+					newflags);
-               error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
                if (error)
                        goto out;

and then the vma owner can do whatever it needs to before calling
mprotect_fixup(), which is already not static.

(how did we get to v33 with this kind of problem still in the patch set?)