diff options
| author | Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> | 2022-07-01 08:57:44 +0200 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2022-07-01 10:02:03 +0200 |
| commit | b75cd218274e01d026dc5240e86fdeb44bbed0c8 (patch) | |
| tree | 240d0abc054709940ef927b4187fa1c6c31201a0 | |
| parent | f63c2c2032c2e3caad9add3b82cc6e91c376fd26 (diff) | |
xen/arm: Fix race in RB-tree based P2M accounting
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>
| -rw-r--r-- | arch/arm/xen/p2m.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/arm/xen/p2m.c b/arch/arm/xen/p2m.c index 84a1cea1f43b..309648c17f48 100644 --- 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(unsigned long pfn, 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 && |