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From: "Derrick, Jonathan" <jonathan.derrick@intel.com>
To: "tglx@linutronix.de" <tglx@linutronix.de>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>,
	"helgaas@kernel.org" <helgaas@kernel.org>
Cc: "Kalakota, SushmaX" <sushmax.kalakota@intel.com>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: [PATCH] PCI: vmd: Keep fwnode allocated through VMD irqdomain life
Date: Sat, 4 Jul 2020 01:44:59 +0000
Message-ID: <225256cc0ef63a3e149bcac97999d06381c52830.camel@intel.com> (raw)
In-Reply-To: <20200630163332.GA3437879@bjorn-Precision-5520>

On Tue, 2020-06-30 at 11:33 -0500, Bjorn Helgaas wrote:
> On Tue, Jun 30, 2020 at 12:39:08PM +0300, Andy Shevchenko wrote:
> > On Mon, Jun 29, 2020 at 06:20:11PM -0500, Bjorn Helgaas wrote:
> > > On Thu, Jun 25, 2020 at 02:58:23PM -0500, Bjorn Helgaas wrote:
> > > > [+cc Thomas]
> > > > 
> > > > On Thu, Jun 25, 2020 at 12:24:49PM -0400, Jon Derrick wrote:
> > > > > From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > > > 
> > > > > The VMD domain does not subscribe to ACPI, and so does not operate on
> > > > > it's irqdomain fwnode. It was freeing the handle after allocation of the
> > > > > domain. As of 181e9d4efaf6a (irqdomain: Make __irq_domain_add() less
> > > > > OF-dependent), the fwnode is put during irq_domain_remove causing a page
> > > > > fault. This patch keeps VMD's fwnode allocated through the lifetime of
> > > > > the VMD irqdomain.
> > > > > 
> > > > > Fixes: ae904cafd59d ("PCI/vmd: Create named irq domain")
> > > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > > > Co-developed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > > > Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> > > > > ---
> > > > > Hi Lorenzo, Bjorn,
> > > > > 
> > > > > Please take this patch for v5.8 fixes. It fixes an issue during VMD
> > > > > unload.
> > > > 
> > > > I tentatively applied this to for-linus for v5.8.
> > > > 
> > > > But I would like to clarify the commit log.  It says this fixes
> > > > Thomas' ae904cafd59d ("PCI/vmd: Create named irq domain").  That
> > > > appeared in v4.13, which suggests that this patch should be backported
> > > > to v4.13 and later.
> > > 
> > > I didn't word this correctly.  What I meant was "I will consider
> > > applying this after the commit log is clarified."  Just FYI that this
> > > isn't resolved yet.
> > > 
> > > Since this is proposed for v5.8, I really want to understand this
> > > better before asking Linus to pull it as a fix.
> > 
> > The problem here is in the original patch which relies on the
> > knowledge that fwnode is (was) not used anyhow specifically for ACPI
> > case. That said, it makes fwnode a dangling pointer which I
> > personally consider as a mine left for others. That's why the Fixes
> > refers to the initial commit. The latter just has been blasted on
> > that mine.
> 
> IIUC, you're saying this pattern:
> 
>   fwnode = irq_domain_alloc_named_id_fwnode(...)
>   irq_domain = pci_msi_create_irq_domain(fwnode, ...)
>   irq_domain_free_fwnode(fwnode)
> 
> leaves a dangling fwnode pointer.  That does look suspicious because
> __irq_domain_add() saves fwnode:
> 
>   irq_domain = pci_msi_create_irq_domain(fwnode, ...)
>     msi_create_irq_domain(fwnode, ...)
>       irq_domain_create_hierarchy(..., fwnode, ...)
> 	irq_domain_create_linear(fwnode, ...)
> 	  __irq_domain_add(fwnode, ...)
> 	    domain->fwnode = fwnode
> 
> and irq_domain_free_fwnode() frees it.  But I'm confused because there
> are several other instances of this pattern:
> 
>   bridge_probe()                      # arch/mips/pci/pci-xtalk-bridge.c
>   mp_irqdomain_create()
>   arch_init_msi_domain()
>   arch_create_remap_msi_irq_domain()
>   dmar_get_irq_domain()
>   hpet_create_irq_domain()
>   ...
> 
> Are they all wrong?  I definitely think it's a bad idea to keep a copy
> of a pointer after we free the data it points to.  But if they're all
> wrong, I don't want to fix just one and leave all the others.
> 
> Thomas, can you enlighten us?
> 

I see that struct irqchip_fwid contains the actual fwnode structure and
when that is freed, it's causes the issue.

I'm noticing in each caller of irq_domain_free_fwnode, we have the
domain itself available. It seems like it should be up to the caller to
deal with the fwnode pointer, but we could just do:

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index a4c2c915511d..61f0070285ff 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -101,7 +101,7 @@ EXPORT_SYMBOL_GPL(__irq_domain_alloc_fwnode);
  *
  * Free a fwnode_handle allocated with irq_domain_alloc_fwnode.
  */
-void irq_domain_free_fwnode(struct fwnode_handle *fwnode)
+void irq_domain_free_fwnode(struct irq_domain *domain, struct
fwnode_handle *fwnode)
 {
        struct irqchip_fwid *fwid;
 
@@ -109,6 +109,7 @@ void irq_domain_free_fwnode(struct fwnode_handle
*fwnode)
                return;
 
        fwid = container_of(fwnode, struct irqchip_fwid, fwnode);
+       domain->fwnode = NULL;
        kfree(fwid->name);
        kfree(fwid);
 }



> > If you think that's fine to have such trick, feel free to update Fixes tag.
> > 
> > > > But it's not clear to me that ae904cafd59d is actually broken, since
> > > > the log also says the problem appeared after 181e9d4efaf6 ("irqdomain:
> > > > Make __irq_domain_add() less OF-dependent"), which we just merged for
> > > > v5.8-rc1.
> > > > 
> > > > And obviously, freeing the fwnode doesn't *cause* a page fault.  A
> > > > use-after-free might cause a fault, but it's not clear where that
> > > > happens.  I guess fwnode is used in the interval between:
> > > > 
> > > >   vmd_enable_domain
> > > >     pci_msi_create_irq_domain
> > > > 
> > > >   ...        <-- fwnode used here somewhere
> > > > 
> > > >   vmd_remove
> > > >     vmd_cleanup_srcu
> > > >       irq_domain_free_fwnode
> > > > 
> > > > But I can't tell how 181e9d4efaf6a and/or ae904cafd59d are related to
> > > > that.
> > > > 
> > > > >  drivers/pci/controller/vmd.c | 8 ++++++--
> > > > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > > > > index e386d4eac407..ebec0a6e77ed 100644
> > > > > --- a/drivers/pci/controller/vmd.c
> > > > > +++ b/drivers/pci/controller/vmd.c
> > > > > @@ -546,9 +546,10 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
> > > > >  
> > > > >  	vmd->irq_domain = pci_msi_create_irq_domain(fn, &vmd_msi_domain_info,
> > > > >  						    x86_vector_domain);
> > > > > -	irq_domain_free_fwnode(fn);
> > > > > -	if (!vmd->irq_domain)
> > > > > +	if (!vmd->irq_domain) {
> > > > > +		irq_domain_free_fwnode(fn);
> > > > >  		return -ENODEV;
> > > > > +	}
> > > > >  
> > > > >  	pci_add_resource(&resources, &vmd->resources[0]);
> > > > >  	pci_add_resource_offset(&resources, &vmd->resources[1], offset[0]);
> > > > > @@ -559,6 +560,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
> > > > >  	if (!vmd->bus) {
> > > > >  		pci_free_resource_list(&resources);
> > > > >  		irq_domain_remove(vmd->irq_domain);
> > > > > +		irq_domain_free_fwnode(fn);
> > > > >  		return -ENODEV;
> > > > >  	}
> > > > >  
> > > > > @@ -672,6 +674,7 @@ static void vmd_cleanup_srcu(struct vmd_dev *vmd)
> > > > >  static void vmd_remove(struct pci_dev *dev)
> > > > >  {
> > > > >  	struct vmd_dev *vmd = pci_get_drvdata(dev);
> > > > > +	struct fwnode_handle *fn = vmd->irq_domain->fwnode;
> > > > >  
> > > > >  	sysfs_remove_link(&vmd->dev->dev.kobj, "domain");
> > > > >  	pci_stop_root_bus(vmd->bus);
> > > > > @@ -679,6 +682,7 @@ static void vmd_remove(struct pci_dev *dev)
> > > > >  	vmd_cleanup_srcu(vmd);
> > > > >  	vmd_detach_resources(vmd);
> > > > >  	irq_domain_remove(vmd->irq_domain);
> > > > > +	irq_domain_free_fwnode(fn);
> > > > >  }
> > > > >  
> > > > >  #ifdef CONFIG_PM_SLEEP
> > > > > -- 
> > > > > 2.18.1
> > > > > 
> > 
> > -- 
> > With Best Regards,
> > Andy Shevchenko
> > 
> > 

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-25 16:24 Jon Derrick
2020-06-25 16:24 ` Jon Derrick
2020-06-25 19:58 ` Bjorn Helgaas
2020-06-25 20:21   ` Derrick, Jonathan
2020-06-29 23:20   ` Bjorn Helgaas
2020-06-30  9:39     ` Andy Shevchenko
2020-06-30 16:33       ` Bjorn Helgaas
2020-07-04  1:44         ` Derrick, Jonathan [this message]
2020-07-04 12:04           ` andriy.shevchenko
2020-07-14 15:40           ` Thomas Gleixner
2020-07-14 15:43             ` Derrick, Jonathan
2020-07-06 10:47         ` Thomas Gleixner
2020-07-06 11:18           ` Andy Shevchenko
2020-07-06 13:30             ` Thomas Gleixner
2020-07-06 15:44               ` Bjorn Helgaas
2020-07-09  9:53                 ` [PATCH] irqdomain/treewide: Keep firmware node unconditionally allocated Thomas Gleixner
2020-07-09 12:00                   ` Marc Zyngier
2020-07-09 21:47                   ` Bjorn Helgaas

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