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KVM: arm64: Fix host stage-2 PGD refcount

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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
This commit is contained in:
Quentin Perret 2021-10-05 10:01:41 +01:00 committed by Marc Zyngier
parent e840f42a49
commit 1d58a17ef5
3 changed files with 27 additions and 1 deletions
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1
arch/arm64/kvm/hyp/include/nvhe/gfp.h
View File

@ -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);

13
arch/arm64/kvm/hyp/nvhe/mem_protect.c
View File

@ -35,7 +35,18 @@ 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)

14
arch/arm64/kvm/hyp/nvhe/page_alloc.c
View File

@ -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;