From: Dan Williams dan.j.williams@intel.com
commit e686c32590f40bffc45f105c04c836ffad3e531a upstream.
While experimenting with CXL region removal the following corruption of /proc/iomem appeared.
Before: f010000000-f04fffffff : CXL Window 0 f010000000-f02fffffff : region4 f010000000-f02fffffff : dax4.0 f010000000-f02fffffff : System RAM (kmem)
After (modprobe -r cxl_test): f010000000-f02fffffff : **redacted binary garbage** f010000000-f02fffffff : System RAM (kmem)
...and testing further the same is visible with persistent memory assigned to kmem:
Before: 480000000-243fffffff : Persistent Memory 480000000-57e1fffff : namespace3.0 580000000-243fffffff : dax3.0 580000000-243fffffff : System RAM (kmem)
After (ndctl disable-region all): 480000000-243fffffff : Persistent Memory 580000000-243fffffff : ***redacted binary garbage*** 580000000-243fffffff : System RAM (kmem)
The corrupted data is from a use-after-free of the "dax4.0" and "dax3.0" resources, and it also shows that the "System RAM (kmem)" resource is not being removed. The bug does not appear after "modprobe -r kmem", it requires the parent of "dax4.0" and "dax3.0" to be removed which re-parents the leaked "System RAM (kmem)" instances. Those in turn reference the freed resource as a parent.
First up for the fix is release_mem_region_adjustable() needs to reliably delete the resource inserted by add_memory_driver_managed(). That is thwarted by a check for IORESOURCE_SYSRAM that predates the dax/kmem driver, from commit:
65c78784135f ("kernel, resource: check for IORESOURCE_SYSRAM in release_mem_region_adjustable")
That appears to be working around the behavior of HMM's "MEMORY_DEVICE_PUBLIC" facility that has since been deleted. With that check removed the "System RAM (kmem)" resource gets removed, but corruption still occurs occasionally because the "dax" resource is not reliably removed.
The dax range information is freed before the device is unregistered, so the driver can not reliably recall (another use after free) what it is meant to release. Lastly if that use after free got lucky, the driver was covering up the leak of "System RAM (kmem)" due to its use of release_resource() which detaches, but does not free, child resources. The switch to remove_resource() forces remove_memory() to be responsible for the deletion of the resource added by add_memory_driver_managed().
Fixes: c2f3011ee697 ("device-dax: add an allocation interface for device-dax instances") Cc: stable@vger.kernel.org Cc: Oscar Salvador osalvador@suse.de Cc: David Hildenbrand david@redhat.com Cc: Pavel Tatashin pasha.tatashin@soleen.com Reviewed-by: Vishal Verma vishal.l.verma@intel.com Reviewed-by: Pasha Tatashin pasha.tatashin@soleen.com Reviewed-by: Dave Jiang dave.jiang@intel.com Link: https://lore.kernel.org/r/167653656244.3147810.5705900882794040229.stgit@dwi... Signed-off-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/dax/bus.c | 2 +- drivers/dax/kmem.c | 4 ++-- kernel/resource.c | 14 -------------- 3 files changed, 3 insertions(+), 17 deletions(-)
--- a/drivers/dax/bus.c +++ b/drivers/dax/bus.c @@ -397,8 +397,8 @@ static void unregister_dev_dax(void *dev dev_dbg(dev, "%s\n", __func__);
kill_dev_dax(dev_dax); - free_dev_dax_ranges(dev_dax); device_del(dev); + free_dev_dax_ranges(dev_dax); put_device(dev); }
--- a/drivers/dax/kmem.c +++ b/drivers/dax/kmem.c @@ -135,7 +135,7 @@ static int dev_dax_kmem_probe(struct dev if (rc) { dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n", i, range.start, range.end); - release_resource(res); + remove_resource(res); kfree(res); data->res[i] = NULL; if (mapped) @@ -181,7 +181,7 @@ static void dev_dax_kmem_remove(struct d
rc = remove_memory(range.start, range_len(&range)); if (rc == 0) { - release_resource(data->res[i]); + remove_resource(data->res[i]); kfree(data->res[i]); data->res[i] = NULL; success++; --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1325,20 +1325,6 @@ retry: continue; }
- /* - * All memory regions added from memory-hotplug path have the - * flag IORESOURCE_SYSTEM_RAM. If the resource does not have - * this flag, we know that we are dealing with a resource coming - * from HMM/devm. HMM/devm use another mechanism to add/release - * a resource. This goes via devm_request_mem_region and - * devm_release_mem_region. - * HMM/devm take care to release their resources when they want, - * so if we are dealing with them, let us just back off here. - */ - if (!(res->flags & IORESOURCE_SYSRAM)) { - break; - } - if (!(res->flags & IORESOURCE_MEM)) break;