[PATCH 5.14 022/169] KVM: arm64: Fix host stage-2 PGD refcount

Greg Kroah-Hartman
2021-10-25T19:46:58Z

From: Quentin Perret <qperret@google.com>

[ Upstream commit 1d58a17ef54599506d44c45ac95be27273a4d2b1 ]

The KVM page-table library refcounts the pages of concatenated stage-2
PGDs individually. However, when running KVM in protected mode, the
host's stage-2 PGD is currently managed by EL2 as a single high-order
compound page, which can cause the refcount of the tail pages to reach 0
when they shouldn't, hence corrupting the page-table.

Fix this by introducing a new hyp_split_page() helper in the EL2 page
allocator (matching the kernel's split_page() function), and make use of
it from host_s2_zalloc_pages_exact().

Fixes: 1025c8c0c6ac ("KVM: arm64: Wrap the host with a stage 2")
Acked-by: Will Deacon <will@kernel.org>
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211005090155.734578-5-qperret@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kvm/hyp/include/nvhe/gfp.h | 1 +
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 13 ++++++++++++-
arch/arm64/kvm/hyp/nvhe/page_alloc.c | 14 ++++++++++++++
3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/gfp.h b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
index fb0f523d1492..0a048dc06a7d 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/gfp.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
@@ -24,6 +24,7 @@ struct hyp_pool {

/* Allocation */
void *hyp_alloc_pages(struct hyp_pool *pool, unsigned short order);
+void hyp_split_page(struct hyp_page *page);
void hyp_get_page(struct hyp_pool *pool, void *addr);
void hyp_put_page(struct hyp_pool *pool, void *addr);

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index a6ce991b1467..b79ce0059e7b 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -35,7 +35,18 @@ static const u8 pkvm_hyp_id = 1;

static void *host_s2_zalloc_pages_exact(size_t size)
{
- return hyp_alloc_pages(&host_s2_pool, get_order(size));
+ void *addr = hyp_alloc_pages(&host_s2_pool, get_order(size));
+
+ hyp_split_page(hyp_virt_to_page(addr));
+
+ /*
+ * The size of concatenated PGDs is always a power of two of PAGE_SIZE,
+ * so there should be no need to free any of the tail pages to make the
+ * allocation exact.
+ */
+ WARN_ON(size != (PAGE_SIZE << get_order(size)));
+
+ return addr;
}

static void *host_s2_zalloc_page(void *pool)
diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
index 41fc25bdfb34..a6e874e61a40 100644
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -193,6 +193,20 @@ void hyp_get_page(struct hyp_pool *pool, void *addr)
hyp_spin_unlock(&pool->lock);
}

+void hyp_split_page(struct hyp_page *p)
+{
+ unsigned short order = p->order;
+ unsigned int i;
+
+ p->order = 0;
+ for (i = 1; i < (1 << order); i++) {
+ struct hyp_page *tail = p + i;
+
+ tail->order = 0;
+ hyp_set_page_refcounted(tail);
+ }
+}
+
void *hyp_alloc_pages(struct hyp_pool *pool, unsigned short order)
{
unsigned short i = order;
--
2.33.0