From 1d58a17ef54599506d44c45ac95be27273a4d2b1 Mon Sep 17 00:00:00 2001 From: Quentin Perret Date: Tue, 5 Oct 2021 10:01:41 +0100 Subject: [PATCH 1/3] KVM: arm64: Fix host stage-2 PGD refcount 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 Suggested-by: Will Deacon Signed-off-by: Quentin Perret Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20211005090155.734578-5-qperret@google.com --- 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 bacd493a4eac..34eeb524b686 100644 --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c @@ -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) 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; From 7615c2a514788559c6684234b8fc27f3a843c2c6 Mon Sep 17 00:00:00 2001 From: Quentin Perret Date: Tue, 5 Oct 2021 10:01:42 +0100 Subject: [PATCH 2/3] KVM: arm64: Report corrupted refcount at EL2 Some of the refcount manipulation helpers used at EL2 are instrumented to catch a corrupted state, but not all of them are treated equally. Let's make things more consistent by instrumenting hyp_page_ref_dec_and_test() as well. Acked-by: Will Deacon Suggested-by: Will Deacon Signed-off-by: Quentin Perret Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20211005090155.734578-6-qperret@google.com --- arch/arm64/kvm/hyp/nvhe/page_alloc.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c index a6e874e61a40..0bd7701ad1df 100644 --- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c +++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c @@ -152,6 +152,7 @@ static inline void hyp_page_ref_inc(struct hyp_page *p) static inline int hyp_page_ref_dec_and_test(struct hyp_page *p) { + BUG_ON(!p->refcount); p->refcount--; return (p->refcount == 0); } From 6e6a8ef088e1222cb1250942f51ad9c1ab219ab2 Mon Sep 17 00:00:00 2001 From: Quentin Perret Date: Tue, 5 Oct 2021 13:20:31 +0100 Subject: [PATCH 3/3] KVM: arm64: Release mmap_lock when using VM_SHARED with MTE VM_SHARED mappings are currently forbidden in a memslot with MTE to prevent two VMs racing to sanitise the same page. However, this check is performed while holding current->mm's mmap_lock, but fails to release it. Fix this by releasing the lock when needed. Fixes: ea7fc1bb1cd1 ("KVM: arm64: Introduce MTE VM feature") Signed-off-by: Quentin Perret Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20211005122031.809857-1-qperret@google.com --- arch/arm64/kvm/mmu.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 1a94a7ca48f2..69bd1732a299 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1529,8 +1529,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, * when updating the PG_mte_tagged page flag, see * sanitise_mte_tags for more details. */ - if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED) - return -EINVAL; + if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED) { + ret = -EINVAL; + break; + } if (vma->vm_flags & VM_PFNMAP) { /* IO region dirty page logging not allowed */