Commit 7a3796d2 authored by Marc Zyngier's avatar Marc Zyngier Committed by Christoffer Dall
Browse files

KVM: arm/arm64: Preserve Exec permission across R/W permission faults 



So far, we loose the Exec property whenever we take permission
faults, as we always reconstruct the PTE/PMD from scratch. This
can be counter productive as we can end-up with the following
fault sequence:

	X -> RO -> ROX -> RW -> RWX

Instead, we can lookup the existing PTE/PMD and clear the XN bit in the
new entry if it was already cleared in the old one, leadig to a much
nicer fault sequence:

	X -> ROX -> RWX

Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
parent a9c0e12e

arch/arm/include/asm/kvm_mmu.h

+10 −0
Original line number Diff line number Diff line
@@ -107,6 +107,11 @@ static inline bool kvm_s2pte_readonly(pte_t *pte) 
	return (pte_val(*pte) & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY;

}



static inline bool kvm_s2pte_exec(pte_t *pte)

{

	return !(pte_val(*pte) & L_PTE_XN);

}



static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)

{

	pmd_val(*pmd) = (pmd_val(*pmd) & ~L_PMD_S2_RDWR) | L_PMD_S2_RDONLY;
@@ -117,6 +122,11 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd) 
	return (pmd_val(*pmd) & L_PMD_S2_RDWR) == L_PMD_S2_RDONLY;

}



static inline bool kvm_s2pmd_exec(pmd_t *pmd)

{

	return !(pmd_val(*pmd) & PMD_SECT_XN);

}



static inline bool kvm_page_empty(void *ptr)

{

	struct page *ptr_page = virt_to_page(ptr);

arch/arm64/include/asm/kvm_mmu.h

+10 −0
Original line number Diff line number Diff line
@@ -203,6 +203,11 @@ static inline bool kvm_s2pte_readonly(pte_t *pte) 
	return (pte_val(*pte) & PTE_S2_RDWR) == PTE_S2_RDONLY;

}



static inline bool kvm_s2pte_exec(pte_t *pte)

{

	return !(pte_val(*pte) & PTE_S2_XN);

}



static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)

{

	kvm_set_s2pte_readonly((pte_t *)pmd);
@@ -213,6 +218,11 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd) 
	return kvm_s2pte_readonly((pte_t *)pmd);

}



static inline bool kvm_s2pmd_exec(pmd_t *pmd)

{

	return !(pmd_val(*pmd) & PMD_S2_XN);

}



static inline bool kvm_page_empty(void *ptr)

{

	struct page *ptr_page = virt_to_page(ptr);

virt/kvm/arm/mmu.c

+27 −0
Original line number Diff line number Diff line
@@ -926,6 +926,25 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache 
	return 0;

}



static bool stage2_is_exec(struct kvm *kvm, phys_addr_t addr)

{

	pmd_t *pmdp;

	pte_t *ptep;



	pmdp = stage2_get_pmd(kvm, NULL, addr);

	if (!pmdp || pmd_none(*pmdp) || !pmd_present(*pmdp))

		return false;



	if (pmd_thp_or_huge(*pmdp))

		return kvm_s2pmd_exec(pmdp);



	ptep = pte_offset_kernel(pmdp, addr);

	if (!ptep || pte_none(*ptep) || !pte_present(*ptep))

		return false;



	return kvm_s2pte_exec(ptep);

}



static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,

			  phys_addr_t addr, const pte_t *new_pte,

			  unsigned long flags)
@@ -1407,6 +1426,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, 
		if (exec_fault) {

			new_pmd = kvm_s2pmd_mkexec(new_pmd);

			invalidate_icache_guest_page(vcpu, pfn, PMD_SIZE);

		} else if (fault_status == FSC_PERM) {

			/* Preserve execute if XN was already cleared */

			if (stage2_is_exec(kvm, fault_ipa))

				new_pmd = kvm_s2pmd_mkexec(new_pmd);

		}



		ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
@@ -1425,6 +1448,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, 
		if (exec_fault) {

			new_pte = kvm_s2pte_mkexec(new_pte);

			invalidate_icache_guest_page(vcpu, pfn, PAGE_SIZE);

		} else if (fault_status == FSC_PERM) {

			/* Preserve execute if XN was already cleared */

			if (stage2_is_exec(kvm, fault_ipa))

				new_pte = kvm_s2pte_mkexec(new_pte);

		}



		ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, flags);

CRA Git | Maintained and supported by SUSTech CRA and CCSE