Messages in this thread Patch in this message | | | Date | Tue, 5 Nov 2019 12:05:11 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] EDAC, ghes: Fix locking and memory barrier issues |
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On Fri, Oct 25, 2019 at 09:13:14PM +0000, Robert Richter wrote: > The ghes registration and refcount is broken in several ways: > > * ghes_edac_register() returns with success for a 2nd instance even > if a first instance is still running.
How?
There's
if (atomic_inc_return(&ghes_init) > 1) return 0;
there. How would a second instance bypass this?
> * The refcount was increased even if a registration failed. This > leads to stale counters preventing the device from being released.
That I see - the return path should dec ghes_init.
> * The ghes refcount may not be decremented properly on > unregistration. Always decrement the refcount once > ghes_edac_unregister() is called to keep the refcount sane.
Right.
> * The ghes_pvt pointer is handed to the irq handler before > registration finished. > > * The mci structure could be freed while the irq handler is running. > > Fix this by adding a mutex to ghes_edac_register(). This mutex > serializes instances to register and unregister. The refcount is only > increased if the registration succeeded. This makes sure the refcount > is in a consistent state after registering or unregistering a device. > Note: A spinlock cannot be used here as the code section may sleep. > > The ghes_pvt is protected by ghes_lock now.
This better be documented in the driver with a comment above the ghes_pvt thing.
I'm assuming the support for multiple instances is going ontop of this? If so, ghes_pvt needs to be an array or so. Also, if you do that, I think you should use mc_devices - see edac_mc_find() et al - instead of growing a special one just for this driver.
> This ensures the pointer > is not updated before registration was finished or while the irq > handler is running. It is unset before unregistering the device > including necessary (implicit) memory barriers making the changes > visible to other cpus. Thus, the device can not be used anymore by an > interrupt. > > A refcount is needed. There can be multiple GHES structures being > defined (see ACPI 6.3 specification, 18.3.2.7 Generic Hardware Error > Source, "Some platforms may describe multiple Generic Hardware Error > Source structures with different notification types, ..."). > > Another approach to use the mci's device refcount (get_device()) and > have a release function does not work here. A release function will be > called only for device_release() with the last put_device() call. The > device must be deleted *before* that with device_del(). This is only > possible by maintaining an own refcount. > > Fixes: 0fe5f281f749 ("EDAC, ghes: Model a single, logical memory controller") > Fixes: 1e72e673b9d1 ("EDAC/ghes: Fix Use after free in ghes_edac remove path") > Signed-off-by: Borislav Petkov <bp@suse.de> > Signed-off-by: James Morse <james.morse@arm.com> > Signed-off-by: Robert Richter <rrichter@marvell.com> > --- > drivers/edac/ghes_edac.c | 78 ++++++++++++++++++++++++++++------------ > 1 file changed, 56 insertions(+), 22 deletions(-)
...
> @@ -457,10 +461,12 @@ static struct acpi_platform_list plat_list[] = { > int ghes_edac_register(struct ghes *ghes, struct device *dev) > { > bool fake = false; > - int rc, num_dimm = 0; > + int rc = 0, num_dimm = 0; > struct mem_ctl_info *mci; > + struct ghes_edac_pvt *pvt; > struct edac_mc_layer layers[1]; > struct ghes_edac_dimm_fill dimm_fill; > + unsigned long flags; > int idx = -1; > > if (IS_ENABLED(CONFIG_X86)) { > @@ -472,11 +478,14 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev) > idx = 0; > } > > + /* finish another registration/unregistration instance first */ > + mutex_lock(&ghes_reg_mutex); > + > /* > * We have only one logical memory controller to which all DIMMs belong. > */ > - if (atomic_inc_return(&ghes_init) > 1) > - return 0; > + if (atomic_inc_not_zero(&ghes_init))
That should probably be called ghes_instances now to make it obvious what it is.
Also, you can make it a normal variable now since it is being modified under the mutex only.
> + goto unlock; > > /* Get the number of DIMMs */ > dmi_walk(ghes_edac_count_dimms, &num_dimm); > @@ -494,12 +503,13 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev) > mci = edac_mc_alloc(0, ARRAY_SIZE(layers), layers, sizeof(struct ghes_edac_pvt)); > if (!mci) { > pr_info("Can't allocate memory for EDAC data\n"); > - return -ENOMEM; > + rc = -ENOMEM; > + goto unlock; > } > > - ghes_pvt = mci->pvt_info; > - ghes_pvt->ghes = ghes; > - ghes_pvt->mci = mci; > + pvt = mci->pvt_info; > + pvt->ghes = ghes; > + pvt->mci = mci; > > mci->pdev = dev; > mci->mtype_cap = MEM_FLAG_EMPTY; > @@ -541,23 +551,47 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev) > if (rc < 0) { > pr_info("Can't register at EDAC core\n"); > edac_mc_free(mci); > - return -ENODEV; > + rc = -ENODEV;
This needs to "goto unlock".
> } > - return 0; > + > + spin_lock_irqsave(&ghes_lock, flags); > + ghes_pvt = pvt; > + spin_unlock_irqrestore(&ghes_lock, flags); > + > + /* only increment on success */ > + atomic_inc(&ghes_init); > + > +unlock: > + mutex_unlock(&ghes_reg_mutex); > + > + return rc; > }
-- Regards/Gruss, Boris.
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