RE: [PATCH] virt: acrn: obtain pa from VMA with PFNMAP flag

["Huang, Yonghua" <yonghua.huang@intel.com>]

Hi Daniel,

 Thank you for this info, we will fix this issue.

Almost miss this mail, sorry!

-Yonghua

> -----Original Message-----
> From: Daniel Vetter <daniel@ffwll.ch>
> Sent: Wednesday, August 10, 2022 20:20
> To: Huang, Yonghua <yonghua.huang@intel.com>
> Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> stable@vger.kernel.org; Chatre, Reinette <reinette.chatre@intel.com>; Wang,
> Zhi A <zhi.a.wang@intel.com>; Wang, Yu1 <yu1.wang@intel.com>; Li, Fei1
> <fei1.li@intel.com>; Linux MM <linux-mm@kvack.org>; DRI Development <dri-
> devel@lists.freedesktop.org>
> Subject: Re: [PATCH] virt: acrn: obtain pa from VMA with PFNMAP flag
> 
> On Mon, Feb 28, 2022 at 05:22:12AM +0300, Yonghua Huang wrote:
> >  acrn_vm_ram_map can't pin the user pages with VM_PFNMAP flag  by
> > calling get_user_pages_fast(), the PA(physical pages)  may be mapped
> > by kernel driver and set PFNMAP flag.
> >
> >  This patch fixes logic to setup EPT mapping for PFN mapped RAM region
> > by checking the memory attribute before adding EPT mapping for them.
> >
> > Fixes: 88f537d5e8dd ("virt: acrn: Introduce EPT mapping management")
> > Signed-off-by: Yonghua Huang <yonghua.huang@intel.com>
> > Signed-off-by: Fei Li <fei1.li@intel.com>
> > ---
> >  drivers/virt/acrn/mm.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c index
> > c4f2e15c8a2b..3b1b1e7a844b 100644
> > --- a/drivers/virt/acrn/mm.c
> > +++ b/drivers/virt/acrn/mm.c
> > @@ -162,10 +162,34 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct
> acrn_vm_memmap *memmap)
> >  	void *remap_vaddr;
> >  	int ret, pinned;
> >  	u64 user_vm_pa;
> > +	unsigned long pfn;
> > +	struct vm_area_struct *vma;
> >
> >  	if (!vm || !memmap)
> >  		return -EINVAL;
> >
> > +	mmap_read_lock(current->mm);
> > +	vma = vma_lookup(current->mm, memmap->vma_base);
> > +	if (vma && ((vma->vm_flags & VM_PFNMAP) != 0)) {
> > +		if ((memmap->vma_base + memmap->len) > vma->vm_end) {
> > +			mmap_read_unlock(current->mm);
> > +			return -EINVAL;
> > +		}
> > +
> > +		ret = follow_pfn(vma, memmap->vma_base, &pfn);
> 
> This races, don't use follow_pfn() and most definitely don't add new users. In
> some cases follow_pte, but the pte/pfn is still only valid for as long as you hold
> the pte spinlock.
> 
> > +		mmap_read_unlock(current->mm);
> 
> Definitely after here there's zero guarantees about this pfn and it could point at
> anything.
> 
> Please fix, I tried pretty hard to get rid of follow_pfn(), but some of them are
> just too hard to fix (e.g. kvm needs a pretty hug rewrite to get it all sorted).
> 
> Cheers, Daniel
> 
> > +		if (ret < 0) {
> > +			dev_dbg(acrn_dev.this_device,
> > +				"Failed to lookup PFN at VMA:%pK.\n", (void
> *)memmap->vma_base);
> > +			return ret;
> > +		}
> > +
> > +		return acrn_mm_region_add(vm, memmap->user_vm_pa,
> > +			 PFN_PHYS(pfn), memmap->len,
> > +			 ACRN_MEM_TYPE_WB, memmap->attr);
> > +	}
> > +	mmap_read_unlock(current->mm);
> > +
> >  	/* Get the page number of the map region */
> >  	nr_pages = memmap->len >> PAGE_SHIFT;
> >  	pages = vzalloc(nr_pages * sizeof(struct page *));
> >
> > base-commit: 73878e5eb1bd3c9656685ca60bc3a49d17311e0c
> > --
> > 2.25.1
> >
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch