Commit 968a85b1 authored Apr 04, 2019 by Chris Wilson Committed by Zhenyu Wang Apr 08, 2019

drm/i915/gvt: Prevent use-after-free in ppgtt_free_all_spt()

ppgtt_free_all_spt() iterates the radixtree as it is deleting it,
forgoing all protection against the leaves being freed in the process
(leaving the iter pointing into the void).

A minimal fix seems to be to use the available post_shadow_list to
decompose the tree into a list prior to destroying the radixtree.

Alerted by the sparse warnings:

drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **
drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **
drivers/gpu/drm/i915/gvt/gtt.c:758:45: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/i915/gvt/gtt.c:758:45: expected void [noderef] <asn:4> **slot
drivers/gpu/drm/i915/gvt/gtt.c:758:45: got void **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void [noderef] <asn:4> **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **

This would also have been loudly warning if run through CI for the
invalid RCU dereferences.

Fixes: b6c126a3 ("drm/i915/gvt: Manage shadow pages with radix tree")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Changbin Du <changbin.du@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

parent 196a6627

drivers/gpu/drm/i915/gvt/gtt.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -750,14 +750,20 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)

		static void ppgtt_free_all_spt(struct intel_vgpu *vgpu)
		{
		struct intel_vgpu_ppgtt_spt *spt;
		struct intel_vgpu_ppgtt_spt spt, spn;
		struct radix_tree_iter iter;
		void **slot;
		LIST_HEAD(all_spt);
		void __rcu **slot;

		rcu_read_lock();
		radix_tree_for_each_slot(slot, &vgpu->gtt.spt_tree, &iter, 0) {
		spt = radix_tree_deref_slot(slot);
		ppgtt_free_spt(spt);
		list_move(&spt->post_shadow_list, &all_spt);
		}
		rcu_read_unlock();

		list_for_each_entry_safe(spt, spn, &all_spt, post_shadow_list)
		ppgtt_free_spt(spt);
		}

		static int ppgtt_handle_guest_write_page_table_bytes(

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