[PATCH 07/14] KVM: arm64: Restrict host access to the ITS tables

Sebastian Ene
2026-03-10T12:50:16Z

Setup shadow structures for ITS indirect tables held in
the GITS_BASER<n> registers.
Make the last level of the Device Table and vPE Table
inacessible to the host.
In a direct layout configuration, donate the table to
the hypervisor since the software is not expected to
program them directly.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
arch/arm64/kvm/hyp/nvhe/its_emulate.c | 143 ++++++++++++++++++++++++++
1 file changed, 143 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/its_emulate.c b/arch/arm64/kvm/hyp/nvhe/its_emulate.c
index 4a3ccc90a1a9..865a5d6353ed 100644
--- a/arch/arm64/kvm/hyp/nvhe/its_emulate.c
+++ b/arch/arm64/kvm/hyp/nvhe/its_emulate.c
@@ -141,6 +141,145 @@ static struct pkvm_protected_reg *get_region(phys_addr_t dev_addr)
return NULL;
}

+static int pkvm_host_unmap_last_level(void *shadow, size_t num_pages, u32 psz)
+{
+ u64 *table = shadow;
+ int ret, i, end = (num_pages << PAGE_SHIFT) / sizeof(table);
+ phys_addr_t table_addr;
+
+ for (i = 0; i < end; i++) {
+ if (!(table[i] & GITS_BASER_VALID))
+ continue;
+
+ table_addr = table[i] & PHYS_MASK;
+ ret = __pkvm_host_donate_hyp(hyp_phys_to_pfn(table_addr), psz >> PAGE_SHIFT);
+ if (ret)
+ goto err_donate;
+ }
+
+ return 0;
+err_donate:
+ for (i = i - 1; i >= 0; i--) {
+ if (!(table[i] & GITS_BASER_VALID))
+ continue;
+
+ table_addr = table[i] & PHYS_MASK;
+ __pkvm_hyp_donate_host(hyp_phys_to_pfn(table_addr), psz >> PAGE_SHIFT);
+ }
+ return ret;
+}
+
+static int pkvm_share_shadow_table(void *shadow, u64 nr_pages)
+{
+ u64 i, ret, start_pfn = hyp_virt_to_pfn(shadow);
+
+ for (i = 0; i < nr_pages; i++) {
+ ret = __pkvm_host_share_hyp(start_pfn + i);
+ if (ret)
+ goto unshare;
+ }
+
+ ret = hyp_pin_shared_mem(shadow, shadow + (nr_pages << PAGE_SHIFT));
+ if (ret)
+ goto unshare;
+
+ return ret;
+unshare:
+ for (i = i - 1; i >= 0; i--)
+ __pkvm_host_unshare_hyp(start_pfn + i);
+ return ret;
+}
+
+static void pkvm_unshare_shadow_table(void *shadow, u64 nr_pages)
+{
+ u64 i, start_pfn = hyp_virt_to_pfn(shadow);
+
+ hyp_unpin_shared_mem(shadow, shadow + (nr_pages << PAGE_SHIFT));
+
+ for (i = 0; i < nr_pages; i++)
+ WARN_ON(__pkvm_host_unshare_hyp(start_pfn + i));
+}
+
+static void pkvm_host_map_last_level(void *shadow, size_t num_pages, u32 psz)
+{
+ u64 *table;
+ int i, end = (num_pages << PAGE_SHIFT) / sizeof(table);
+ phys_addr_t table_addr;
+
+ for (i = 0; i < end; i++) {
+ if (!(table[i] & GITS_BASER_VALID))
+ continue;
+
+ table_addr = table[i] & ~GITS_BASER_VALID;
+ WARN_ON(__pkvm_hyp_donate_host(hyp_phys_to_pfn(table_addr), psz >> PAGE_SHIFT));
+ }
+}
+
+static int pkvm_setup_its_shadow_baser(struct its_shadow_tables *shadow)
+{
+ int i, ret;
+ u64 baser_val, num_pages, type;
+ void *base, *host_base;
+
+ for (i = 0; i < GITS_BASER_NR_REGS; i++) {
+ baser_val = shadow->tables[i].val;
+ if (!(baser_val & GITS_BASER_VALID))
+ continue;
+
+ base = kern_hyp_va(shadow->tables[i].base);
+ num_pages = (1 << shadow->tables[i].order);
+
+ ret = __pkvm_host_donate_hyp(hyp_virt_to_pfn(base), num_pages);
+ if (ret)
+ goto err_donate;
+
+ if (baser_val & GITS_BASER_INDIRECT) {
+ host_base = kern_hyp_va(shadow->tables[i].shadow);
+ ret = pkvm_share_shadow_table(host_base, num_pages);
+ if (ret)
+ goto err_with_donation;
+
+ type = GITS_BASER_TYPE(baser_val);
+ if (type == GITS_BASER_TYPE_COLLECTION)
+ continue;
+
+ ret = pkvm_host_unmap_last_level(base, num_pages,
+ shadow->tables[i].psz);
+ if (ret)
+ goto err_with_share;
+ }
+ }
+
+ return 0;
+err_with_share:
+ pkvm_unshare_shadow_table(host_base, num_pages);
+err_with_donation:
+ __pkvm_hyp_donate_host(hyp_virt_to_pfn(base), num_pages);
+err_donate:
+ for (i = i - 1; i >= 0; i--) {
+ baser_val = shadow->tables[i].val;
+ if (!(baser_val & GITS_BASER_VALID))
+ continue;
+
+ base = kern_hyp_va(shadow->tables[i].base);
+ num_pages = (1 << shadow->tables[i].order);
+
+ WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(base), num_pages));
+ if (baser_val & GITS_BASER_INDIRECT) {
+ host_base = kern_hyp_va(shadow->tables[i].shadow);
+ pkvm_unshare_shadow_table(host_base, num_pages);
+
+ type = GITS_BASER_TYPE(baser_val);
+ if (type == GITS_BASER_TYPE_COLLECTION)
+ continue;
+
+ pkvm_host_map_last_level(base, num_pages, shadow->tables[i].psz);
+ }
+ }
+
+ return ret;
+}
+
static int pkvm_setup_its_shadow_cmdq(struct its_shadow_tables *shadow)
{
int ret, i, num_pages;
@@ -205,6 +344,10 @@ int pkvm_init_gic_its_emulation(phys_addr_t dev_addr, void *host_priv_state,
if (ret)
goto err_with_shadow;

+ ret = pkvm_setup_its_shadow_baser(shadow);
+ if (ret)
+ goto err_with_shadow;
+
its_reg->priv = priv_state;

hyp_spin_lock_init(&priv_state->its_lock);
--
2.53.0.473.g4a7958ca14-goog