[Xen-devel] [PATCH v1 4/6] x86/hvm: Add SMAP support to HVM guest

[Feng Wu <feng.wu@xxxxxxxxx>]

Intel new CPU supports SMAP (Supervisor Mode Access Prevention).
SMAP prevents supervisor-mode accesses to any linear address with
a valid translation for which the U/S flag (bit 2) is 1 in every
paging-structure entry controlling the translation for the linear
address.

This patch enable SMAP for HVM geust.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c        |  3 +++
 xen/arch/x86/mm/guest_walk.c  | 27 +++++++++++++++++++++++----
 xen/include/asm-x86/hvm/hvm.h | 13 +++++++++++++
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index b0da8e7..b52476d 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3036,6 +3036,9 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
unsigned int *ebx,
         if ( (count == 0) && !cpu_has_smep )
             *ebx &= ~cpufeat_mask(X86_FEATURE_SMEP);
 
+        if ( (count == 0) && !cpu_has_smap )
+            *ebx &= ~cpufeat_mask(X86_FEATURE_SMAP);
+
         /* Don't expose MPX to hvm when VMX support is not available */
         if ( (count == 0) &&
              (!(vmx_vmexit_control & VM_EXIT_CLEAR_BNDCFGS) ||
diff --git a/xen/arch/x86/mm/guest_walk.c b/xen/arch/x86/mm/guest_walk.c
index 70460b6..1d5f1fc 100644
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -29,6 +29,7 @@
 #include <xen/sched.h>
 #include <asm/page.h>
 #include <asm/guest_pt.h>
+#include <asm/hvm/vmx/vmx.h>
 
 
 /* Flags that are needed in a pagetable entry, with the sense of NX inverted */
@@ -144,14 +145,18 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
     guest_l4e_t *l4p;
 #endif
     uint32_t gflags, mflags, iflags, rc = 0;
-    int smep;
+    int smep, smap;
     bool_t pse1G = 0, pse2M = 0;
+    unsigned long sel = 0;
+    uint64_t eflags = guest_cpu_user_regs()->eflags;
     p2m_query_t qt = P2M_ALLOC | P2M_UNSHARE;
 
     perfc_incr(guest_walk);
     memset(gw, 0, sizeof(*gw));
     gw->va = va;
 
+    __vmread(GUEST_CS_SELECTOR, &sel);
+
     /* Mandatory bits that must be set in every entry.  We invert NX and
      * the invalid bits, to calculate as if there were an "X" bit that
      * allowed access.  We will accumulate, in rc, the set of flags that
@@ -165,7 +170,21 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
      * whole walk as if it were a user-mode one and then invert the answer. */
     smep = (is_hvm_vcpu(v) && hvm_smep_enabled(v) 
             && (pfec & PFEC_insn_fetch) && !(pfec & PFEC_user_mode) );
-    if ( smep )
+
+    /*
+     * SMAP: kernel-mode data accesses from user-mode mappings should fault
+     * A fault is considered as a SMAP violation if the following
+     * conditions come ture:
+     *   - X86_CR4_SMAP is set in CR4
+     *   - An user page is accessed
+     *   - CPL = 3 or X86_EFLAGS_AC clear set)
+     *   - Page fault in kernel mode
+     */
+    smap = ( is_hvm_vcpu(v) && hvm_smap_enabled(v)
+            && !(!((sel & 3) == 3) && (eflags & X86_EFLAGS_AC))
+            && !(pfec & PFEC_user_mode) );
+
+    if ( smep || smap )
         mflags |= _PAGE_USER;
 
 #if GUEST_PAGING_LEVELS >= 3 /* PAE or 64... */
@@ -338,8 +357,8 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
 #if GUEST_PAGING_LEVELS >= 4 /* 64-bit only... */
 set_ad:
 #endif
-    /* Now re-invert the user-mode requirement for SMEP. */
-    if ( smep ) 
+    /* Now re-invert the user-mode requirement for SMEP and SMAP */
+    if ( smep || smap )
         rc ^= _PAGE_USER;
 
     /* Go back and set accessed and dirty bits only if the walk was a
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index dcc3483..b703b93 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -257,6 +257,8 @@ int hvm_girq_dest_2_vcpu_id(struct domain *d, uint8_t dest, 
uint8_t dest_mode);
     (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_PAE))
 #define hvm_smep_enabled(v) \
     (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_SMEP))
+#define hvm_smap_enabled(v) \
+    (hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_SMAP))
 #define hvm_nx_enabled(v) \
     (!!((v)->arch.hvm_vcpu.guest_efer & EFER_NX))
 
@@ -363,6 +365,16 @@ static inline int hvm_event_pending(struct vcpu *v)
 #define HVM_CR4_HOST_MASK (mmu_cr4_features & \
     (X86_CR4_VMXE | X86_CR4_PAE | X86_CR4_MCE))
 
+static inline bool_t hvm_cpuid_has_smap(void)
+{
+    unsigned int eax = 0, ebx = 0, ecx = 0, edx = 0;
+    unsigned int leaf = 0x7;
+
+    hvm_cpuid(leaf, &eax, &ebx, &ecx, &edx);
+
+    return !!(ebx & cpufeat_mask(X86_FEATURE_SMAP));
+}
+
 /* These bits in CR4 cannot be set by the guest. */
 #define HVM_CR4_GUEST_RESERVED_BITS(_v)                 \
     (~((unsigned long)                                  \
@@ -371,6 +383,7 @@ static inline int hvm_event_pending(struct vcpu *v)
         X86_CR4_MCE | X86_CR4_PGE | X86_CR4_PCE |       \
         X86_CR4_OSFXSR | X86_CR4_OSXMMEXCPT |           \
         (cpu_has_smep ? X86_CR4_SMEP : 0) |             \
+        (hvm_cpuid_has_smap() ? X86_CR4_SMAP : 0) |     \
         (cpu_has_fsgsbase ? X86_CR4_FSGSBASE : 0) |     \
         ((nestedhvm_enabled((_v)->domain) && cpu_has_vmx)\
                       ? X86_CR4_VMXE : 0)  |             \
-- 
1.8.3.1


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