[PATCH 15/15] arm/arm64: KVM: Check that IDMAP doesn't intersect with VA range

Marc Zyngier
2016-06-07T10:58:35Z

This is more of a safety measure than anything else: If we end-up
with an idmap page that intersect with the range picked for the
the HYP VA space, abort the KVM setup, as it is unsafe to go
further.

I cannot imagine it happening on 64bit (we have a mechanism to
work around it), but could potentially occur on a 32bit system with
the kernel loaded high enough in memory so that in conflicts with
the kernel VA.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm/kvm/mmu.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 46b8604..819517d 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1708,6 +1708,21 @@ int kvm_mmu_init(void)
*/
BUG_ON((hyp_idmap_start ^ (hyp_idmap_end - 1)) & PAGE_MASK);

+ kvm_info("IDMAP page: %lx\n", hyp_idmap_start);
+ kvm_info("HYP VA range: %lx:%lx\n",
+ KERN_TO_HYP(PAGE_OFFSET), KERN_TO_HYP(~0UL));
+
+ if (hyp_idmap_start >= KERN_TO_HYP(PAGE_OFFSET) &&
+ hyp_idmap_start < KERN_TO_HYP(~0UL)) {
+ /*
+ * The idmap page is intersecting with the VA space,
+ * it is not safe to continue further.
+ */
+ kvm_err("IDMAP intersecting with HYP VA, unable to continue\n");
+ err = -EINVAL;
+ goto out;
+ }
+
hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, hyp_pgd_order);
if (!hyp_pgd) {
kvm_err("Hyp mode PGD not allocated\n");
--
2.1.4