Subject: [PATCH] KVM: arm64: Use BTI for pKVM

From: Mostafa Saleh <[email-masked]>
Date: Tue, 16 May 2023 14:18:46 +0000

CONFIG_ARM64_BTI_KERNEL compiles the kernel to support ARMv8.5-BTI.
However, the nvhe code doesn't make use of it as it doesn't map any
pages with Guarded Page(GP) bit.

This patch maps pKVM .text section with GP bit which matches the
kernel handling for BTI.

A new flag is added to enum kvm_pgtable_prot: KVM_PGTABLE_PROT_GP_S1,
which represents BTI guarded page in hypervisor stage-1 page table.

Signed-off-by: Mostafa Saleh <[email-masked]>
---
 arch/arm64/include/asm/kvm_pgtable.h | 3 +++
 arch/arm64/kvm/hyp/nvhe/setup.c      | 8 ++++++--
 arch/arm64/kvm/hyp/pgtable.c         | 6 ++++--
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 4cd6762bda80..5bcd06d664d3 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -151,6 +151,7 @@ enum kvm_pgtable_stage2_flags {
  * @KVM_PGTABLE_PROT_W:		Write permission.
  * @KVM_PGTABLE_PROT_R:		Read permission.
  * @KVM_PGTABLE_PROT_DEVICE:	Device attributes.
+ * @KVM_PGTABLE_PROT_GP_S1:	GP(guarded page) used for BTI in stage-1 only
  * @KVM_PGTABLE_PROT_SW0:	Software bit 0.
  * @KVM_PGTABLE_PROT_SW1:	Software bit 1.
  * @KVM_PGTABLE_PROT_SW2:	Software bit 2.
@@ -163,6 +164,8 @@ enum kvm_pgtable_prot {
 
 	KVM_PGTABLE_PROT_DEVICE			= BIT(3),
 
+	KVM_PGTABLE_PROT_GP_S1			= BIT(50),
+
 	KVM_PGTABLE_PROT_SW0			= BIT(55),
 	KVM_PGTABLE_PROT_SW1			= BIT(56),
 	KVM_PGTABLE_PROT_SW2			= BIT(57),
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 110f04627785..95f80e2b2946 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -66,7 +66,7 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 {
 	void *start, *end, *virt = hyp_phys_to_virt(phys);
 	unsigned long pgt_size = hyp_s1_pgtable_pages() << PAGE_SHIFT;
-	enum kvm_pgtable_prot prot;
+	enum kvm_pgtable_prot prot = PAGE_HYP_EXEC;
 	int ret, i;
 
 	/* Recreate the hyp page-table using the early page allocator */
@@ -88,7 +88,11 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 	if (ret)
 		return ret;
 
-	ret = pkvm_create_mappings(__hyp_text_start, __hyp_text_end, PAGE_HYP_EXEC);
+	/* Hypervisor text is mapped as guarded pages(GP). */
+	if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && cpus_have_const_cap(ARM64_BTI))
+		prot |= KVM_PGTABLE_PROT_GP_S1;
+
+	ret = pkvm_create_mappings(__hyp_text_start, __hyp_text_end, prot);
 	if (ret)
 		return ret;
 
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 3d61bd3e591d..028e198acd48 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -145,7 +145,8 @@ static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
 	u64 type = (level == KVM_PGTABLE_MAX_LEVELS - 1) ? KVM_PTE_TYPE_PAGE :
 							   KVM_PTE_TYPE_BLOCK;
 
-	pte |= attr & (KVM_PTE_LEAF_ATTR_LO | KVM_PTE_LEAF_ATTR_HI);
+	pte |= attr & (KVM_PTE_LEAF_ATTR_LO | KVM_PTE_LEAF_ATTR_HI |
+		       KVM_PGTABLE_PROT_GP_S1);
 	pte |= FIELD_PREP(KVM_PTE_TYPE, type);
 	pte |= KVM_PTE_VALID;
 
@@ -378,7 +379,8 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
 	attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_AP, ap);
 	attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S1_SH, sh);
 	attr |= KVM_PTE_LEAF_ATTR_LO_S1_AF;
-	attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
+	attr |= prot & (KVM_PTE_LEAF_ATTR_HI_SW | KVM_PGTABLE_PROT_GP_S1);
+
 	*ptep = attr;
 
 	return 0;
-- 
2.40.1.606.ga4b1b128d6-goog

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