From: Oleksandr Tyshchenko oleksandr_tyshchenko@epam.com
commit b75cd218274e01d026dc5240e86fdeb44bbed0c8 upstream.
During the PV driver life cycle the mappings are added to the RB-tree by set_foreign_p2m_mapping(), which is called from gnttab_map_refs() and are removed by clear_foreign_p2m_mapping() which is called from gnttab_unmap_refs(). As both functions end up calling __set_phys_to_machine_multi() which updates the RB-tree, this function can be called concurrently.
There is already a "p2m_lock" to protect against concurrent accesses, but the problem is that the first read of "phys_to_mach.rb_node" in __set_phys_to_machine_multi() is not covered by it, so this might lead to the incorrect mappings update (removing in our case) in RB-tree.
In my environment the related issue happens rarely and only when PV net backend is running, the xen_add_phys_to_mach_entry() claims that it cannot add new pfn <-> mfn mapping to the tree since it is already exists which results in a failure when mapping foreign pages.
But there might be other bad consequences related to the non-protected root reads such use-after-free, etc.
While at it, also fix the similar usage in __pfn_to_mfn(), so initialize "struct rb_node *n" with the "p2m_lock" held in both functions to avoid possible bad consequences.
This is CVE-2022-33744 / XSA-406.
Signed-off-by: Oleksandr Tyshchenko oleksandr_tyshchenko@epam.com Reviewed-by: Stefano Stabellini sstabellini@kernel.org Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm/xen/p2m.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/arm/xen/p2m.c +++ b/arch/arm/xen/p2m.c @@ -63,11 +63,12 @@ out:
unsigned long __pfn_to_mfn(unsigned long pfn) { - struct rb_node *n = phys_to_mach.rb_node; + struct rb_node *n; struct xen_p2m_entry *entry; unsigned long irqflags;
read_lock_irqsave(&p2m_lock, irqflags); + n = phys_to_mach.rb_node; while (n) { entry = rb_entry(n, struct xen_p2m_entry, rbnode_phys); if (entry->pfn <= pfn && @@ -152,10 +153,11 @@ bool __set_phys_to_machine_multi(unsigne int rc; unsigned long irqflags; struct xen_p2m_entry *p2m_entry; - struct rb_node *n = phys_to_mach.rb_node; + struct rb_node *n;
if (mfn == INVALID_P2M_ENTRY) { write_lock_irqsave(&p2m_lock, irqflags); + n = phys_to_mach.rb_node; while (n) { p2m_entry = rb_entry(n, struct xen_p2m_entry, rbnode_phys); if (p2m_entry->pfn <= pfn &&