linux-kernel - Re: [PATCH v13 04/26] KVM: guest_memfd: Fix PTR_ERR() handling in __kvm_gmem_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri, 19 Apr 2024 10:11:09 -0500
From: Michael Roth <michael.roth@....com>
To: David Hildenbrand <david@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
	<linux-crypto@...r.kernel.org>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<jroedel@...e.de>, <thomas.lendacky@....com>, <hpa@...or.com>,
	<ardb@...nel.org>, <pbonzini@...hat.com>, <seanjc@...gle.com>,
	<vkuznets@...hat.com>, <jmattson@...gle.com>, <luto@...nel.org>,
	<dave.hansen@...ux.intel.com>, <slp@...hat.com>, <pgonda@...gle.com>,
	<peterz@...radead.org>, <srinivas.pandruvada@...ux.intel.com>,
	<rientjes@...gle.com>, <dovmurik@...ux.ibm.com>, <tobin@....com>,
	<bp@...en8.de>, <vbabka@...e.cz>, <kirill@...temov.name>,
	<ak@...ux.intel.com>, <tony.luck@...el.com>,
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, <alpergun@...gle.com>,
	<jarkko@...nel.org>, <ashish.kalra@....com>, <nikunj.dadhania@....com>,
	<pankaj.gupta@....com>, <liam.merwick@...cle.com>
Subject: Re: [PATCH v13 04/26] KVM: guest_memfd: Fix PTR_ERR() handling in
 __kvm_gmem_get_pfn()

On Fri, Apr 19, 2024 at 02:58:43PM +0200, David Hildenbrand wrote:
> On 18.04.24 21:41, Michael Roth wrote:
> > kvm_gmem_get_folio() may return a PTR_ERR() rather than just NULL. In
> > particular, for cases where EEXISTS is returned when FGP_CREAT_ONLY
> > flag is used. Handle this properly in __kvm_gmem_get_pfn().
> > 
> > Signed-off-by: Michael Roth <michael.roth@....com>
> > ---
> >   virt/kvm/guest_memfd.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> > index ccf22e44f387..9d7c6a70c547 100644
> > --- a/virt/kvm/guest_memfd.c
> > +++ b/virt/kvm/guest_memfd.c
> > @@ -580,8 +580,8 @@ static int __kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot,
> >   	}
> >   	folio = kvm_gmem_get_folio(file_inode(file), index, prepare);
> > -	if (!folio)
> > -		return -ENOMEM;
> > +	if (IS_ERR_OR_NULL(folio))
> > +		return folio ? PTR_ERR(folio) : -ENOMEM;
> 
> Will it even return NULL?  Staring at other filemap_grab_folio() users, they
> all check for IS_ERR().

Looks like the NULL case is handled with PTR_ERR(-ENOENT), so IS_ERR()
would be sufficient. I think in the past kvm_gmem_get_folio() itself
would return NULL in some cases, but as of commit 2b01b7e994e95 that's
no longer the case.

I'll fix this up to expect only PTR_ERR() when I re-spin v14, and also
address the other kvm_gmem_get_folio() / __filemap_get_folio() call
sites.

> 
> >   	if (folio_test_hwpoison(folio)) {
> >   		r = -EHWPOISON;
> 
> Do we have a Fixes: tag?

Fixes: 2b01b7e994e95 ("KVM: guest_memfd: pass error up from filemap_grab_folio")

Will add that in the re-spin as well.

Thanks!

-Mike

> 
> -- 
> Cheers,
> 
> David / dhildenb
>