[PATCH v3 0/4] KVM: enable Intel SMAP for KVM

[PATCH v3 0/4] KVM: enable Intel SMAP for KVM

[Feng Wu]

Supervisor Mode Access Prevention (SMAP) is a new security feature 
disclosed by Intel, please refer to the following document: 

http://software.intel.com/sites/default/files/319433-014.pdf
 
Every access to a linear address is either a supervisor-mode access
or a user-mode access. All accesses performed while the current
privilege level (CPL) is less than 3 are supervisor-mode accesses.
If CPL = 3, accesses are generally user-mode accesses. However, some
operations implicitly access system data structures, and the resulting
accesses to those data structures are supervisor-mode accesses regardless
of CPL. Examples of such implicit supervisor accesses include the following:
accesses to the global descriptor table (GDT) or local descriptor table
(LDT) to load a segment descriptor; accesses to the interrupt descriptor
table (IDT) when delivering an interrupt or exception; and accesses to the
task-state segment (TSS) as part of a task switch or change of CPL.

If CR4.SMAP = 1, supervisor-mode data accesses are not allowed to linear
addresses that are accessible in user mode. If CPL < 3, SMAP protections
are disabled if EFLAGS.AC = 1. If CPL = 3, SMAP applies to all supervisor-mode
data accesses (these are implicit supervisor accesses) regardless of the
value of EFLAGS.AC.

This patchset pass-through SMAP feature to guests, and let guests
benefit from it.

Version 1:
  * Remove SMAP bit from CR4_RESERVED_BITS.
  * Add SMAP support when setting CR4
  * Disable SMAP for guests in EPT realmode and EPT unpaging mode
  * Expose SMAP feature to guest

Version 2:
  * Change the logic of updating mmu permission bitmap for SMAP violation
  * Expose SMAP feature to guest in the last patch of this series.

Version 3:
  * Changes in update_permission_bitmask().
  * Use a branchless way suggested by Paolo Bonzini to detect SMAP
    violation in permission_fault(). 

Feng Wu (4):
  KVM: Remove SMAP bit from CR4_RESERVED_BITS.
  KVM: Add SMAP support when setting CR4
  KVM: Disable SMAP for guests in EPT realmode and EPT unpaging mode
  KVM: expose SMAP feature to guest

 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/cpuid.c            |  2 +-
 arch/x86/kvm/cpuid.h            |  8 ++++++++
 arch/x86/kvm/mmu.c              | 35 +++++++++++++++++++++++++++++---
 arch/x86/kvm/mmu.h              | 44 +++++++++++++++++++++++++++++++++--------
 arch/x86/kvm/paging_tmpl.h      |  2 +-
 arch/x86/kvm/vmx.c              | 11 ++++++-----
 arch/x86/kvm/x86.c              |  9 ++++++++-
 8 files changed, 93 insertions(+), 20 deletions(-)

-- 
1.8.3.1

[PATCH v3 1/4] KVM: Remove SMAP bit from CR4_RESERVED_BITS.

[Feng Wu]

This patch removes SMAP bit from CR4_RESERVED_BITS.

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fdf83af..4eeb049 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -60,7 +60,7 @@
 			  | X86_CR4_PSE | X86_CR4_PAE | X86_CR4_MCE     \
 			  | X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
 			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
-			  | X86_CR4_OSXMMEXCPT | X86_CR4_VMXE))
+			  | X86_CR4_OSXMMEXCPT | X86_CR4_VMXE | X86_CR4_SMAP))
 
 #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
 
-- 
1.8.3.1

[PATCH v3 2/4] KVM: Add SMAP support when setting CR4

[Feng Wu]

This patch adds SMAP handling logic when setting CR4 for guests

Thanks a lot to Paolo Bonzini for his suggestion to use the branchless
way to detect SMAP violation.

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
 arch/x86/kvm/cpuid.h       |  8 ++++++++
 arch/x86/kvm/mmu.c         | 35 ++++++++++++++++++++++++++++++++---
 arch/x86/kvm/mmu.h         | 44 ++++++++++++++++++++++++++++++++++++--------
 arch/x86/kvm/paging_tmpl.h |  2 +-
 arch/x86/kvm/x86.c         |  9 ++++++++-
 5 files changed, 85 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index a2a1bb7..eeecbed 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -48,6 +48,14 @@ static inline bool guest_cpuid_has_smep(struct kvm_vcpu *vcpu)
 	return best && (best->ebx & bit(X86_FEATURE_SMEP));
 }
 
+static inline bool guest_cpuid_has_smap(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry(vcpu, 7, 0);
+	return best && (best->ebx & bit(X86_FEATURE_SMAP));
+}
+
 static inline bool guest_cpuid_has_fsgsbase(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best;
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9b53135..5a1ed38 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3601,20 +3601,28 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu,
 	}
 }
 
-static void update_permission_bitmask(struct kvm_vcpu *vcpu,
+void update_permission_bitmask(struct kvm_vcpu *vcpu,
 		struct kvm_mmu *mmu, bool ept)
 {
 	unsigned bit, byte, pfec;
 	u8 map;
-	bool fault, x, w, u, wf, uf, ff, smep;
+	bool fault, x, w, u, wf, uf, ff, smapf, cr4_smap, smep, smap = 0;
 
 	smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
+	cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
 	for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) {
 		pfec = byte << 1;
 		map = 0;
 		wf = pfec & PFERR_WRITE_MASK;
 		uf = pfec & PFERR_USER_MASK;
 		ff = pfec & PFERR_FETCH_MASK;
+		/*
+		 * PFERR_RSVD_MASK bit is used to detect SMAP violation.
+		 * We will check it in permission_fault(), this bit is
+		 * set in pfec for normal fault, while it is cleared for
+		 * SMAP violations.
+		 */
+		smapf = !(pfec & PFERR_RSVD_MASK);
 		for (bit = 0; bit < 8; ++bit) {
 			x = bit & ACC_EXEC_MASK;
 			w = bit & ACC_WRITE_MASK;
@@ -3627,11 +3635,32 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
 				w |= !is_write_protection(vcpu) && !uf;
 				/* Disallow supervisor fetches of user code if cr4.smep */
 				x &= !(smep && u && !uf);
+
+				/*
+				 * SMAP:kernel-mode data accesses from user-mode
+				 * mappings should fault. A fault is considered
+				 * as a SMAP violation if all of the following
+				 * conditions are ture:
+				 *   - X86_CR4_SMAP is set in CR4
+				 *   - An user page is accessed
+				 *   - Page fault in kernel mode
+				 *   - !(CPL<3 && X86_EFLAGS_AC is set)
+				 *
+				 *   Here, we cover the first three conditions,
+				 *   The CPL and X86_EFLAGS_AC is in smapf,which
+				 *   permission_fault() computes dynamically.
+				 *
+				 *   Also, SMAP does not affect instruction
+				 *   fetches, add the !ff check here to make it
+				 *   clearer.
+				 */
+				smap = cr4_smap && u && !uf && !ff;
 			} else
 				/* Not really needed: no U/S accesses on ept  */
 				u = 1;
 
-			fault = (ff && !x) || (uf && !u) || (wf && !w);
+			fault = (ff && !x) || (uf && !u) || (wf && !w) ||
+				(smapf && smap);
 			map |= fault << bit;
 		}
 		mmu->permissions[byte] = map;
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 2926152..822190f 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -44,11 +44,17 @@
 #define PT_DIRECTORY_LEVEL 2
 #define PT_PAGE_TABLE_LEVEL 1
 
-#define PFERR_PRESENT_MASK (1U << 0)
-#define PFERR_WRITE_MASK (1U << 1)
-#define PFERR_USER_MASK (1U << 2)
-#define PFERR_RSVD_MASK (1U << 3)
-#define PFERR_FETCH_MASK (1U << 4)
+#define PFERR_PRESENT_BIT 0
+#define PFERR_WRITE_BIT 1
+#define PFERR_USER_BIT 2
+#define PFERR_RSVD_BIT 3
+#define PFERR_FETCH_BIT 4
+
+#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
+#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
+#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
+#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
+#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
 
 int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
 void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
@@ -73,6 +79,8 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
 void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
 		bool execonly);
+void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
+		bool ept);
 
 static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
 {
@@ -110,10 +118,30 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu)
  * Will a fault with a given page-fault error code (pfec) cause a permission
  * fault with the given access (in ACC_* format)?
  */
-static inline bool permission_fault(struct kvm_mmu *mmu, unsigned pte_access,
-				    unsigned pfec)
+static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
+				    unsigned pte_access, unsigned pfec)
 {
-	return (mmu->permissions[pfec >> 1] >> pte_access) & 1;
+	int cpl = kvm_x86_ops->get_cpl(vcpu);
+	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
+
+	/*
+	 * If CPL < 3, SMAP prevention are disabled if EFLAGS.AC = 1.
+	 *
+	 * If CPL = 3, SMAP applies to all supervisor-mode data accesses
+	 * (these are implicit supervisor accesses) regardless of the value
+	 * of EFLAGS.AC.
+	 *
+	 * This computes (cpl < 3) && (rflags & X86_EFLAGS_AC), leaving
+	 * the result in X86_EFLAGS_AC. We then insert it in place of
+	 * the PFERR_RSVD_MASK bit; this bit will always be zero in pfec,
+	 * but it will be one in index if SMAP checks are being overridden.
+	 * It is important to keep this branchless.
+	 */
+	unsigned long smap = (cpl-3) & (rflags & X86_EFLAGS_AC);
+	int index = (pfec >> 1) +
+		    (smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));
+
+	return (mmu->permissions[index] >> pte_access) & 1;
 }
 
 void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index cba218a..4107765 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -353,7 +353,7 @@ retry_walk:
 		walker->ptes[walker->level - 1] = pte;
 	} while (!is_last_gpte(mmu, walker->level, pte));
 
-	if (unlikely(permission_fault(mmu, pte_access, access))) {
+	if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
 		errcode |= PFERR_PRESENT_MASK;
 		goto error;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2b85784..5869c6d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -646,6 +646,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 	if (!guest_cpuid_has_smep(vcpu) && (cr4 & X86_CR4_SMEP))
 		return 1;
 
+	if (!guest_cpuid_has_smap(vcpu) && (cr4 & X86_CR4_SMAP))
+		return 1;
+
 	if (!guest_cpuid_has_fsgsbase(vcpu) && (cr4 & X86_CR4_FSGSBASE))
 		return 1;
 
@@ -674,6 +677,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
 		kvm_mmu_reset_context(vcpu);
 
+	if ((cr4 ^ old_cr4) & X86_CR4_SMAP)
+		update_permission_bitmask(vcpu, vcpu->arch.walk_mmu, false);
+
 	if ((cr4 ^ old_cr4) & X86_CR4_OSXSAVE)
 		kvm_update_cpuid(vcpu);
 
@@ -4108,7 +4114,8 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
 		| (write ? PFERR_WRITE_MASK : 0);
 
 	if (vcpu_match_mmio_gva(vcpu, gva)
-	    && !permission_fault(vcpu->arch.walk_mmu, vcpu->arch.access, access)) {
+	    && !permission_fault(vcpu, vcpu->arch.walk_mmu,
+				 vcpu->arch.access, access)) {
 		*gpa = vcpu->arch.mmio_gfn << PAGE_SHIFT |
 					(gva & (PAGE_SIZE - 1));
 		trace_vcpu_match_mmio(gva, *gpa, write, false);
-- 
1.8.3.1

Re: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4

[Paolo Bonzini]

Just a few comments...

> -static void update_permission_bitmask(struct kvm_vcpu *vcpu,
> +void update_permission_bitmask(struct kvm_vcpu *vcpu,
>  		struct kvm_mmu *mmu, bool ept)
>  {
>  	unsigned bit, byte, pfec;
>  	u8 map;
> -	bool fault, x, w, u, wf, uf, ff, smep;
> +	bool fault, x, w, u, wf, uf, ff, smapf, cr4_smap, smep, smap = 0;
>
>  	smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);

Can you make an additional patch to rename this to cr4_smep?

> +	cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
>  	for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) {
>  		pfec = byte << 1;
>  		map = 0;
>  		wf = pfec & PFERR_WRITE_MASK;
>  		uf = pfec & PFERR_USER_MASK;
>  		ff = pfec & PFERR_FETCH_MASK;
> +		/*
> +		 * PFERR_RSVD_MASK bit is used to detect SMAP violation.
> +		 * We will check it in permission_fault(), this bit is
> +		 * set in pfec for normal fault, while it is cleared for
> +		 * SMAP violations.
> +		 */

"This bit is set in PFEC if we the access is _not_ subject to SMAP 
restrictions, and cleared otherwise.  The bit is only meaningful if
the SMAP bit is set in CR4."

> +		smapf = !(pfec & PFERR_RSVD_MASK);
>  		for (bit = 0; bit < 8; ++bit) {
>  			x = bit & ACC_EXEC_MASK;
>  			w = bit & ACC_WRITE_MASK;
> @@ -3627,11 +3635,32 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
>  				w |= !is_write_protection(vcpu) && !uf;
>  				/* Disallow supervisor fetches of user code if cr4.smep */
>  				x &= !(smep && u && !uf);
> +
> +				/*
> +				 * SMAP:kernel-mode data accesses from user-mode
> +				 * mappings should fault. A fault is considered
> +				 * as a SMAP violation if all of the following
> +				 * conditions are ture:
> +				 *   - X86_CR4_SMAP is set in CR4
> +				 *   - An user page is accessed
> +				 *   - Page fault in kernel mode
> +				 *   - !(CPL<3 && X86_EFLAGS_AC is set)

- if CPL < 3, EFLAGS.AC is clear

> +				 *   Here, we cover the first three conditions,
> +				 *   The CPL and X86_EFLAGS_AC is in smapf,which
> +				 *   permission_fault() computes dynamically.

The fourth is computed dynamically in permission_fault() and is in SMAPF.

> +				 *   Also, SMAP does not affect instruction
> +				 *   fetches, add the !ff check here to make it
> +				 *   clearer.
> +				 */
> +				smap = cr4_smap && u && !uf && !ff;
>  			} else
>  				/* Not really needed: no U/S accesses on ept  */
>  				u = 1;
>
> -			fault = (ff && !x) || (uf && !u) || (wf && !w);
> +			fault = (ff && !x) || (uf && !u) || (wf && !w) ||
> +				(smapf && smap);
>  			map |= fault << bit;
>  		}
>  		mmu->permissions[byte] = map;
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 2926152..822190f 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -44,11 +44,17 @@
>  #define PT_DIRECTORY_LEVEL 2
>  #define PT_PAGE_TABLE_LEVEL 1
>
> -#define PFERR_PRESENT_MASK (1U << 0)
> -#define PFERR_WRITE_MASK (1U << 1)
> -#define PFERR_USER_MASK (1U << 2)
> -#define PFERR_RSVD_MASK (1U << 3)
> -#define PFERR_FETCH_MASK (1U << 4)
> +#define PFERR_PRESENT_BIT 0
> +#define PFERR_WRITE_BIT 1
> +#define PFERR_USER_BIT 2
> +#define PFERR_RSVD_BIT 3
> +#define PFERR_FETCH_BIT 4
> +
> +#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
> +#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
> +#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
> +#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
> +#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
>
>  int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
>  void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
> @@ -73,6 +79,8 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
>  void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
>  void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
>  		bool execonly);
> +void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> +		bool ept);
>
>  static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
>  {
> @@ -110,10 +118,30 @@ static inline bool is_write_protection(struct kvm_vcpu *vcpu)
>   * Will a fault with a given page-fault error code (pfec) cause a permission
>   * fault with the given access (in ACC_* format)?
>   */
> -static inline bool permission_fault(struct kvm_mmu *mmu, unsigned pte_access,
> -				    unsigned pfec)
> +static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> +				    unsigned pte_access, unsigned pfec)
>  {
> -	return (mmu->permissions[pfec >> 1] >> pte_access) & 1;
> +	int cpl = kvm_x86_ops->get_cpl(vcpu);
> +	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
> +
> +	/*
> +	 * If CPL < 3, SMAP prevention are disabled if EFLAGS.AC = 1.
> +	 *
> +	 * If CPL = 3, SMAP applies to all supervisor-mode data accesses
> +	 * (these are implicit supervisor accesses) regardless of the value
> +	 * of EFLAGS.AC.
> +	 *
> +	 * This computes (cpl < 3) && (rflags & X86_EFLAGS_AC), leaving
> +	 * the result in X86_EFLAGS_AC. We then insert it in place of
> +	 * the PFERR_RSVD_MASK bit; this bit will always be zero in pfec,
> +	 * but it will be one in index if SMAP checks are being overridden.
> +	 * It is important to keep this branchless.
> +	 */
> +	unsigned long smap = (cpl-3) & (rflags & X86_EFLAGS_AC);

Spaces around minus.

> +	int index = (pfec >> 1) +
> +		    (smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));
> +
> +	return (mmu->permissions[index] >> pte_access) & 1;
>  }
>
>  void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index cba218a..4107765 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -353,7 +353,7 @@ retry_walk:
>  		walker->ptes[walker->level - 1] = pte;
>  	} while (!is_last_gpte(mmu, walker->level, pte));
>
> -	if (unlikely(permission_fault(mmu, pte_access, access))) {
> +	if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
>  		errcode |= PFERR_PRESENT_MASK;
>  		goto error;
>  	}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2b85784..5869c6d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -646,6 +646,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  	if (!guest_cpuid_has_smep(vcpu) && (cr4 & X86_CR4_SMEP))
>  		return 1;
>
> +	if (!guest_cpuid_has_smap(vcpu) && (cr4 & X86_CR4_SMAP))
> +		return 1;
> +
>  	if (!guest_cpuid_has_fsgsbase(vcpu) && (cr4 & X86_CR4_FSGSBASE))
>  		return 1;
>
> @@ -674,6 +677,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
>  		kvm_mmu_reset_context(vcpu);
>
> +	if ((cr4 ^ old_cr4) & X86_CR4_SMAP)
> +		update_permission_bitmask(vcpu, vcpu->arch.walk_mmu, false);
> +
>  	if ((cr4 ^ old_cr4) & X86_CR4_OSXSAVE)
>  		kvm_update_cpuid(vcpu);
>
> @@ -4108,7 +4114,8 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
>  		| (write ? PFERR_WRITE_MASK : 0);
>
>  	if (vcpu_match_mmio_gva(vcpu, gva)
> -	    && !permission_fault(vcpu->arch.walk_mmu, vcpu->arch.access, access)) {
> +	    && !permission_fault(vcpu, vcpu->arch.walk_mmu,
> +				 vcpu->arch.access, access)) {
>  		*gpa = vcpu->arch.mmio_gfn << PAGE_SHIFT |
>  					(gva & (PAGE_SIZE - 1));
>  		trace_vcpu_match_mmio(gva, *gpa, write, false);
>

Thanks!

Paolo

RE: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4

[Wu, Feng]

> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On
> Behalf Of Paolo Bonzini
> Sent: Monday, March 31, 2014 9:31 PM
> To: Wu, Feng; gleb@redhat.com; hpa@zytor.com; kvm@vger.kernel.org
> Subject: Re: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4
> 
> Just a few comments...
> 
> > -static void update_permission_bitmask(struct kvm_vcpu *vcpu,
> > +void update_permission_bitmask(struct kvm_vcpu *vcpu,
> >  		struct kvm_mmu *mmu, bool ept)
> >  {
> >  	unsigned bit, byte, pfec;
> >  	u8 map;
> > -	bool fault, x, w, u, wf, uf, ff, smep;
> > +	bool fault, x, w, u, wf, uf, ff, smapf, cr4_smap, smep, smap = 0;
> >
> >  	smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
> 
> Can you make an additional patch to rename this to cr4_smep?

Sure! I noticed your comments about this issue in the previous email, I was prepare to make a patch for it, will send out it today!
> 
> > +	cr4_smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
> >  	for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) {
> >  		pfec = byte << 1;
> >  		map = 0;
> >  		wf = pfec & PFERR_WRITE_MASK;
> >  		uf = pfec & PFERR_USER_MASK;
> >  		ff = pfec & PFERR_FETCH_MASK;
> > +		/*
> > +		 * PFERR_RSVD_MASK bit is used to detect SMAP violation.
> > +		 * We will check it in permission_fault(), this bit is
> > +		 * set in pfec for normal fault, while it is cleared for
> > +		 * SMAP violations.
> > +		 */
> 
> "This bit is set in PFEC if we the access is _not_ subject to SMAP
> restrictions, and cleared otherwise.  The bit is only meaningful if
> the SMAP bit is set in CR4."
> 
> > +		smapf = !(pfec & PFERR_RSVD_MASK);
> >  		for (bit = 0; bit < 8; ++bit) {
> >  			x = bit & ACC_EXEC_MASK;
> >  			w = bit & ACC_WRITE_MASK;
> > @@ -3627,11 +3635,32 @@ static void update_permission_bitmask(struct
> kvm_vcpu *vcpu,
> >  				w |= !is_write_protection(vcpu) && !uf;
> >  				/* Disallow supervisor fetches of user code if cr4.smep */
> >  				x &= !(smep && u && !uf);
> > +
> > +				/*
> > +				 * SMAP:kernel-mode data accesses from user-mode
> > +				 * mappings should fault. A fault is considered
> > +				 * as a SMAP violation if all of the following
> > +				 * conditions are ture:
> > +				 *   - X86_CR4_SMAP is set in CR4
> > +				 *   - An user page is accessed
> > +				 *   - Page fault in kernel mode
> > +				 *   - !(CPL<3 && X86_EFLAGS_AC is set)
> 
> - if CPL < 3, EFLAGS.AC is clear

Should it be "if CPL =3 or EFLAGS.AC is clear" ?

> 
> > +				 *   Here, we cover the first three conditions,
> > +				 *   The CPL and X86_EFLAGS_AC is in smapf,which
> > +				 *   permission_fault() computes dynamically.
> 
> The fourth is computed dynamically in permission_fault() and is in SMAPF.
> 
> > +				 *   Also, SMAP does not affect instruction
> > +				 *   fetches, add the !ff check here to make it
> > +				 *   clearer.
> > +				 */
> > +				smap = cr4_smap && u && !uf && !ff;
> >  			} else
> >  				/* Not really needed: no U/S accesses on ept  */
> >  				u = 1;
> >
> > -			fault = (ff && !x) || (uf && !u) || (wf && !w);
> > +			fault = (ff && !x) || (uf && !u) || (wf && !w) ||
> > +				(smapf && smap);
> >  			map |= fault << bit;
> >  		}
> >  		mmu->permissions[byte] = map;
> > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > index 2926152..822190f 100644
> > --- a/arch/x86/kvm/mmu.h
> > +++ b/arch/x86/kvm/mmu.h
> > @@ -44,11 +44,17 @@
> >  #define PT_DIRECTORY_LEVEL 2
> >  #define PT_PAGE_TABLE_LEVEL 1
> >
> > -#define PFERR_PRESENT_MASK (1U << 0)
> > -#define PFERR_WRITE_MASK (1U << 1)
> > -#define PFERR_USER_MASK (1U << 2)
> > -#define PFERR_RSVD_MASK (1U << 3)
> > -#define PFERR_FETCH_MASK (1U << 4)
> > +#define PFERR_PRESENT_BIT 0
> > +#define PFERR_WRITE_BIT 1
> > +#define PFERR_USER_BIT 2
> > +#define PFERR_RSVD_BIT 3
> > +#define PFERR_FETCH_BIT 4
> > +
> > +#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
> > +#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
> > +#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
> > +#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
> > +#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
> >
> >  int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64
> sptes[4]);
> >  void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
> > @@ -73,6 +79,8 @@ int handle_mmio_page_fault_common(struct
> kvm_vcpu *vcpu, u64 addr, bool direct);
> >  void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu
> *context);
> >  void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu
> *context,
> >  		bool execonly);
> > +void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu
> *mmu,
> > +		bool ept);
> >
> >  static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
> >  {
> > @@ -110,10 +118,30 @@ static inline bool is_write_protection(struct
> kvm_vcpu *vcpu)
> >   * Will a fault with a given page-fault error code (pfec) cause a permission
> >   * fault with the given access (in ACC_* format)?
> >   */
> > -static inline bool permission_fault(struct kvm_mmu *mmu, unsigned
> pte_access,
> > -				    unsigned pfec)
> > +static inline bool permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu
> *mmu,
> > +				    unsigned pte_access, unsigned pfec)
> >  {
> > -	return (mmu->permissions[pfec >> 1] >> pte_access) & 1;
> > +	int cpl = kvm_x86_ops->get_cpl(vcpu);
> > +	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
> > +
> > +	/*
> > +	 * If CPL < 3, SMAP prevention are disabled if EFLAGS.AC = 1.
> > +	 *
> > +	 * If CPL = 3, SMAP applies to all supervisor-mode data accesses
> > +	 * (these are implicit supervisor accesses) regardless of the value
> > +	 * of EFLAGS.AC.
> > +	 *
> > +	 * This computes (cpl < 3) && (rflags & X86_EFLAGS_AC), leaving
> > +	 * the result in X86_EFLAGS_AC. We then insert it in place of
> > +	 * the PFERR_RSVD_MASK bit; this bit will always be zero in pfec,
> > +	 * but it will be one in index if SMAP checks are being overridden.
> > +	 * It is important to keep this branchless.
> > +	 */
> > +	unsigned long smap = (cpl-3) & (rflags & X86_EFLAGS_AC);
> 
> Spaces around minus.
> 
> > +	int index = (pfec >> 1) +
> > +		    (smap >> (X86_EFLAGS_AC_BIT - PFERR_RSVD_BIT + 1));
> > +
> > +	return (mmu->permissions[index] >> pte_access) & 1;
> >  }
> >
> >  void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);
> > diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> > index cba218a..4107765 100644
> > --- a/arch/x86/kvm/paging_tmpl.h
> > +++ b/arch/x86/kvm/paging_tmpl.h
> > @@ -353,7 +353,7 @@ retry_walk:
> >  		walker->ptes[walker->level - 1] = pte;
> >  	} while (!is_last_gpte(mmu, walker->level, pte));
> >
> > -	if (unlikely(permission_fault(mmu, pte_access, access))) {
> > +	if (unlikely(permission_fault(vcpu, mmu, pte_access, access))) {
> >  		errcode |= PFERR_PRESENT_MASK;
> >  		goto error;
> >  	}
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 2b85784..5869c6d 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -646,6 +646,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned
> long cr4)
> >  	if (!guest_cpuid_has_smep(vcpu) && (cr4 & X86_CR4_SMEP))
> >  		return 1;
> >
> > +	if (!guest_cpuid_has_smap(vcpu) && (cr4 & X86_CR4_SMAP))
> > +		return 1;
> > +
> >  	if (!guest_cpuid_has_fsgsbase(vcpu) && (cr4 & X86_CR4_FSGSBASE))
> >  		return 1;
> >
> > @@ -674,6 +677,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned
> long cr4)
> >  	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
> >  		kvm_mmu_reset_context(vcpu);
> >
> > +	if ((cr4 ^ old_cr4) & X86_CR4_SMAP)
> > +		update_permission_bitmask(vcpu, vcpu->arch.walk_mmu, false);
> > +
> >  	if ((cr4 ^ old_cr4) & X86_CR4_OSXSAVE)
> >  		kvm_update_cpuid(vcpu);
> >
> > @@ -4108,7 +4114,8 @@ static int vcpu_mmio_gva_to_gpa(struct
> kvm_vcpu *vcpu, unsigned long gva,
> >  		| (write ? PFERR_WRITE_MASK : 0);
> >
> >  	if (vcpu_match_mmio_gva(vcpu, gva)
> > -	    && !permission_fault(vcpu->arch.walk_mmu, vcpu->arch.access,
> access)) {
> > +	    && !permission_fault(vcpu, vcpu->arch.walk_mmu,
> > +				 vcpu->arch.access, access)) {
> >  		*gpa = vcpu->arch.mmio_gfn << PAGE_SHIFT |
> >  					(gva & (PAGE_SIZE - 1));
> >  		trace_vcpu_match_mmio(gva, *gpa, write, false);
> >
> 
> Thanks!
> 
> Paolo
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Thanks,
Feng

Re: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4

[Paolo Bonzini]

Il 01/04/2014 03:17, Wu, Feng ha scritto:
>>> A fault is considered
>>> > > +				 * as a SMAP violation if all of the following
>>> > > +				 * conditions are ture:
>>> > > +				 *   - X86_CR4_SMAP is set in CR4
>>> > > +				 *   - An user page is accessed
>>> > > +				 *   - Page fault in kernel mode
>>> > > +				 *   - !(CPL<3 && X86_EFLAGS_AC is set)
>> >
>> > - if CPL < 3, EFLAGS.AC is clear
> Should it be "if CPL =3 or EFLAGS.AC is clear" ?
>

What I meant is "if CPL < 3, EFLAGS.AC must also be clear", but your 
version is fine too.  You choose!

Paolo

RE: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4

[Wu, Feng]

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Tuesday, April 01, 2014 5:27 PM
> To: Wu, Feng; gleb@redhat.com; hpa@zytor.com; kvm@vger.kernel.org
> Subject: Re: [PATCH v3 2/4] KVM: Add SMAP support when setting CR4
> 
> Il 01/04/2014 03:17, Wu, Feng ha scritto:
> >>> A fault is considered
> >>> > > +				 * as a SMAP violation if all of the following
> >>> > > +				 * conditions are ture:
> >>> > > +				 *   - X86_CR4_SMAP is set in CR4
> >>> > > +				 *   - An user page is accessed
> >>> > > +				 *   - Page fault in kernel mode
> >>> > > +				 *   - !(CPL<3 && X86_EFLAGS_AC is set)
> >> >
> >> > - if CPL < 3, EFLAGS.AC is clear
> > Should it be "if CPL =3 or EFLAGS.AC is clear" ?
> >
> 
> What I meant is "if CPL < 3, EFLAGS.AC must also be clear", but your
> version is fine too.  You choose!

Thanks for your comments! :)
BTW: I tested nested today, this patch set works well for nested virtualization!
> 
> Paolo

[PATCH v3 3/4] KVM: Disable SMAP for guests in EPT realmode and EPT unpaging mode

[Feng Wu]

SMAP is disabled if CPU is in non-paging mode in hardware.
However KVM always uses paging mode to emulate guest non-paging
mode with TDP. To emulate this behavior, SMAP needs to be
manually disabled when guest switches to non-paging mode.

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
 arch/x86/kvm/vmx.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3927528..e58cb5f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3452,13 +3452,14 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			hw_cr4 &= ~X86_CR4_PAE;
 			hw_cr4 |= X86_CR4_PSE;
 			/*
-			 * SMEP is disabled if CPU is in non-paging mode in
-			 * hardware. However KVM always uses paging mode to
+			 * SMEP/SMAP is disabled if CPU is in non-paging mode
+			 * in hardware. However KVM always uses paging mode to
 			 * emulate guest non-paging mode with TDP.
-			 * To emulate this behavior, SMEP needs to be manually
-			 * disabled when guest switches to non-paging mode.
+			 * To emulate this behavior, SMEP/SMAP needs to be
+			 * manually disabled when guest switches to non-paging
+			 * mode.
 			 */
-			hw_cr4 &= ~X86_CR4_SMEP;
+			hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
 		} else if (!(cr4 & X86_CR4_PAE)) {
 			hw_cr4 &= ~X86_CR4_PAE;
 		}
-- 
1.8.3.1

[PATCH v3 4/4] KVM: expose SMAP feature to guest

[Feng Wu]

This patch exposes SMAP feature to guest

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c697625..deb5f9b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -303,7 +303,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 	/* cpuid 7.0.ebx */
 	const u32 kvm_supported_word9_x86_features =
 		F(FSGSBASE) | F(BMI1) | F(HLE) | F(AVX2) | F(SMEP) |
-		F(BMI2) | F(ERMS) | f_invpcid | F(RTM);
+		F(BMI2) | F(ERMS) | f_invpcid | F(RTM) | F(SMAP);
 
 	/* all calls to cpuid_count() should be made on the same cpu */
 	get_cpu();
-- 
1.8.3.1