KVM: x86 emulator: fix memory access during x86 emulation

Currently when x86 emulator needs to access memory, page walk is done with
broadest permission possible, so if emulated instruction was executed
by userspace process it can still access kernel memory. Fix that by
providing correct memory access to page walker during emulation.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>

5 files changed, 124 insertions, 47 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e4e2df3b6038..c44b46014842 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -616,7 +616,7 @@ static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt,
 
         if (linear < fc->start || linear >= fc->end) {
                 size = min(15UL, PAGE_SIZE - offset_in_page(linear));
-                rc = ops->read_std(linear, fc->data, size, ctxt->vcpu);
+                rc = ops->fetch(linear, fc->data, size, ctxt->vcpu, NULL);
                 if (rc)
                         return rc;
                 fc->start = linear;
@@ -671,11 +671,11 @@ static int read_descriptor(struct x86_emulate_ctxt *ctxt,
                 op_bytes = 3;
         *address = 0;
         rc = ops->read_std((unsigned long)ptr, (unsigned long *)size, 2,
-                           ctxt->vcpu);
+                           ctxt->vcpu, NULL);
         if (rc)
                 return rc;
         rc = ops->read_std((unsigned long)ptr + 2, address, op_bytes,
-                           ctxt->vcpu);
+                           ctxt->vcpu, NULL);
         return rc;
 }
 
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 739793240d1d..741373e8ca77 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -138,12 +138,6 @@ module_param(oos_shadow, bool, 0644);
 #define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | PT_USER_MASK \
                         | PT64_NX_MASK)
 
-#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 RMAP_EXT 4
 
 #define ACC_EXEC_MASK    1
@@ -1632,7 +1626,7 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva)
 {
         struct page *page;
 
-        gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, gva);
+        gpa_t gpa = kvm_mmu_gva_to_gpa_read(vcpu, gva, NULL);
 
         if (gpa == UNMAPPED_GVA)
                 return NULL;
@@ -2155,8 +2149,11 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
         spin_unlock(&vcpu->kvm->mmu_lock);
 }
 
-static gpa_t nonpaging_gva_to_gpa(struct kvm_vcpu *vcpu, gva_t vaddr)
+static gpa_t nonpaging_gva_to_gpa(struct kvm_vcpu *vcpu, gva_t vaddr,
+                                  u32 access, u32 *error)
 {
+        if (error)
+                *error = 0;
         return vaddr;
 }
 
@@ -2740,7 +2737,7 @@ int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
         if (tdp_enabled)
                 return 0;
 
-        gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, gva);
+        gpa = kvm_mmu_gva_to_gpa_read(vcpu, gva, NULL);
 
         spin_lock(&vcpu->kvm->mmu_lock);
         r = kvm_mmu_unprotect_page(vcpu->kvm, gpa >> PAGE_SHIFT);
@@ -3237,7 +3234,7 @@ static void audit_mappings_page(struct kvm_vcpu *vcpu, u64 page_pte,
                 if (is_shadow_present_pte(ent) && !is_last_spte(ent, level))
                         audit_mappings_page(vcpu, ent, va, level - 1);
                 else {
-                        gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, va);
+                        gpa_t gpa = kvm_mmu_gva_to_gpa_read(vcpu, va, NULL);
                         gfn_t gfn = gpa >> PAGE_SHIFT;
                         pfn_t pfn = gfn_to_pfn(vcpu->kvm, gfn);
                         hpa_t hpa = (hpa_t)pfn << PAGE_SHIFT;
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 61ef5a65b7d8..be66759321a5 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -42,6 +42,12 @@
 #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)
+
 int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
 
 static inline void kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index df15a5307d2d..81eab9a50e6a 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -490,18 +490,23 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
         spin_unlock(&vcpu->kvm->mmu_lock);
 }
 
-static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
+static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr, u32 access,
+                               u32 *error)
 {
         struct guest_walker walker;
         gpa_t gpa = UNMAPPED_GVA;
         int r;
 
-        r = FNAME(walk_addr)(&walker, vcpu, vaddr, 0, 0, 0);
+        r = FNAME(walk_addr)(&walker, vcpu, vaddr,
+                             !!(access & PFERR_WRITE_MASK),
+                             !!(access & PFERR_USER_MASK),
+                             !!(access & PFERR_FETCH_MASK));
 
         if (r) {
                 gpa = gfn_to_gpa(walker.gfn);
                 gpa |= vaddr & ~PAGE_MASK;
-        }
+        } else if (error)
+                *error = walker.error_code;
 
         return gpa;
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a28379507d30..ea3a8af8a478 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3039,14 +3039,41 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v)
         return kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, len, v);
 }
 
-static int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
-                               struct kvm_vcpu *vcpu)
+gpa_t kvm_mmu_gva_to_gpa_read(struct kvm_vcpu *vcpu, gva_t gva, u32 *error)
+{
+        u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
+        return vcpu->arch.mmu.gva_to_gpa(vcpu, gva, access, error);
+}
+
+ gpa_t kvm_mmu_gva_to_gpa_fetch(struct kvm_vcpu *vcpu, gva_t gva, u32 *error)
+{
+        u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
+        access |= PFERR_FETCH_MASK;
+        return vcpu->arch.mmu.gva_to_gpa(vcpu, gva, access, error);
+}
+
+gpa_t kvm_mmu_gva_to_gpa_write(struct kvm_vcpu *vcpu, gva_t gva, u32 *error)
+{
+        u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
+        access |= PFERR_WRITE_MASK;
+        return vcpu->arch.mmu.gva_to_gpa(vcpu, gva, access, error);
+}
+
+/* uses this to access any guest's mapped memory without checking CPL */
+gpa_t kvm_mmu_gva_to_gpa_system(struct kvm_vcpu *vcpu, gva_t gva, u32 *error)
+{
+        return vcpu->arch.mmu.gva_to_gpa(vcpu, gva, 0, error);
+}
+
+static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
+                                      struct kvm_vcpu *vcpu, u32 access,
+                                      u32 *error)
 {
         void *data = val;
         int r = X86EMUL_CONTINUE;
 
         while (bytes) {
-                gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+                gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr, access, error);
                 unsigned offset = addr & (PAGE_SIZE-1);
                 unsigned toread = min(bytes, (unsigned)PAGE_SIZE - offset);
                 int ret;
@@ -3069,14 +3096,37 @@ out:
         return r;
 }
 
+/* used for instruction fetching */
+static int kvm_fetch_guest_virt(gva_t addr, void *val, unsigned int bytes,
+                                struct kvm_vcpu *vcpu, u32 *error)
+{
+        u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
+        return kvm_read_guest_virt_helper(addr, val, bytes, vcpu,
+                                          access | PFERR_FETCH_MASK, error);
+}
+
+static int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
+                               struct kvm_vcpu *vcpu, u32 *error)
+{
+        u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
+        return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
+                                          error);
+}
+
+static int kvm_read_guest_virt_system(gva_t addr, void *val, unsigned int bytes,
+                               struct kvm_vcpu *vcpu, u32 *error)
+{
+        return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, 0, error);
+}
+
 static int kvm_write_guest_virt(gva_t addr, void *val, unsigned int bytes,
-                                struct kvm_vcpu *vcpu)
+                                struct kvm_vcpu *vcpu, u32 *error)
 {
         void *data = val;
         int r = X86EMUL_CONTINUE;
 
         while (bytes) {
-                gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+                gpa_t gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, error);
                 unsigned offset = addr & (PAGE_SIZE-1);
                 unsigned towrite = min(bytes, (unsigned)PAGE_SIZE - offset);
                 int ret;
@@ -3106,6 +3156,7 @@ static int emulator_read_emulated(unsigned long addr,
                                   struct kvm_vcpu *vcpu)
 {
         gpa_t                 gpa;
+        u32 error_code;
 
         if (vcpu->mmio_read_completed) {
                 memcpy(val, vcpu->mmio_data, bytes);
@@ -3115,17 +3166,20 @@ static int emulator_read_emulated(unsigned long addr,
                 return X86EMUL_CONTINUE;
         }
 
-        gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+        gpa = kvm_mmu_gva_to_gpa_read(vcpu, addr, &error_code);
+
+        if (gpa == UNMAPPED_GVA) {
+                kvm_inject_page_fault(vcpu, addr, error_code);
+                return X86EMUL_PROPAGATE_FAULT;
+        }
 
         /* For APIC access vmexit */
         if ((gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
                 goto mmio;
 
-        if (kvm_read_guest_virt(addr, val, bytes, vcpu)
+        if (kvm_read_guest_virt(addr, val, bytes, vcpu, NULL)
                                 == X86EMUL_CONTINUE)
                 return X86EMUL_CONTINUE;
-        if (gpa == UNMAPPED_GVA)
-                return X86EMUL_PROPAGATE_FAULT;
 
 mmio:
         /*
@@ -3164,11 +3218,12 @@ static int emulator_write_emulated_onepage(unsigned long addr,
                                            struct kvm_vcpu *vcpu)
 {
         gpa_t                 gpa;
+        u32 error_code;
 
-        gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+        gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, &error_code);
 
         if (gpa == UNMAPPED_GVA) {
-                kvm_inject_page_fault(vcpu, addr, 2);
+                kvm_inject_page_fault(vcpu, addr, error_code);
                 return X86EMUL_PROPAGATE_FAULT;
         }
 
@@ -3232,7 +3287,7 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
                 char *kaddr;
                 u64 val;
 
-                gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+                gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, NULL);
 
                 if (gpa == UNMAPPED_GVA ||
                    (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
@@ -3297,7 +3352,7 @@ void kvm_report_emulation_failure(struct kvm_vcpu *vcpu, const char *context)
 
         rip_linear = rip + get_segment_base(vcpu, VCPU_SREG_CS);
 
-        kvm_read_guest_virt(rip_linear, (void *)opcodes, 4, vcpu);
+        kvm_read_guest_virt(rip_linear, (void *)opcodes, 4, vcpu, NULL);
 
         printk(KERN_ERR "emulation failed (%s) rip %lx %02x %02x %02x %02x\n",
                context, rip, opcodes[0], opcodes[1], opcodes[2], opcodes[3]);
@@ -3305,7 +3360,8 @@ void kvm_report_emulation_failure(struct kvm_vcpu *vcpu, const char *context)
 EXPORT_SYMBOL_GPL(kvm_report_emulation_failure);
 
 static struct x86_emulate_ops emulate_ops = {
-        .read_std            = kvm_read_guest_virt,
+        .read_std            = kvm_read_guest_virt_system,
+        .fetch               = kvm_fetch_guest_virt,
         .read_emulated       = emulator_read_emulated,
         .write_emulated      = emulator_write_emulated,
         .cmpxchg_emulated    = emulator_cmpxchg_emulated,
@@ -3442,12 +3498,17 @@ static int pio_copy_data(struct kvm_vcpu *vcpu)
         gva_t q = vcpu->arch.pio.guest_gva;
         unsigned bytes;
         int ret;
+        u32 error_code;
 
         bytes = vcpu->arch.pio.size * vcpu->arch.pio.cur_count;
         if (vcpu->arch.pio.in)
-                ret = kvm_write_guest_virt(q, p, bytes, vcpu);
+                ret = kvm_write_guest_virt(q, p, bytes, vcpu, &error_code);
         else
-                ret = kvm_read_guest_virt(q, p, bytes, vcpu);
+                ret = kvm_read_guest_virt(q, p, bytes, vcpu, &error_code);
+
+        if (ret == X86EMUL_PROPAGATE_FAULT)
+                kvm_inject_page_fault(vcpu, q, error_code);
+
         return ret;
 }
 
@@ -3468,7 +3529,7 @@ int complete_pio(struct kvm_vcpu *vcpu)
                 if (io->in) {
                         r = pio_copy_data(vcpu);
                         if (r)
-                                return r;
+                                goto out;
                 }
 
                 delta = 1;
@@ -3495,7 +3556,7 @@ int complete_pio(struct kvm_vcpu *vcpu)
                         kvm_register_write(vcpu, VCPU_REGS_RSI, val);
                 }
         }
-
+out:
         io->count -= io->cur_count;
         io->cur_count = 0;
 
@@ -3617,10 +3678,8 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, int in,
         if (!vcpu->arch.pio.in) {
                 /* string PIO write */
                 ret = pio_copy_data(vcpu);
-                if (ret == X86EMUL_PROPAGATE_FAULT) {
-                        kvm_inject_gp(vcpu, 0);
+                if (ret == X86EMUL_PROPAGATE_FAULT)
                         return 1;
-                }
                 if (ret == 0 && !pio_string_write(vcpu)) {
                         complete_pio(vcpu);
                         if (vcpu->arch.pio.count == 0)
@@ -4663,7 +4722,9 @@ static int load_guest_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
                 kvm_queue_exception_e(vcpu, GP_VECTOR, selector & 0xfffc);
                 return X86EMUL_PROPAGATE_FAULT;
         }
-        return kvm_read_guest_virt(dtable.base + index*8, seg_desc, sizeof(*seg_desc), vcpu);
+        return kvm_read_guest_virt_system(dtable.base + index*8,
+                                          seg_desc, sizeof(*seg_desc),
+                                          vcpu, NULL);
 }
 
 /* allowed just for 8 bytes segments */
@@ -4677,15 +4738,23 @@ static int save_guest_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
 
         if (dtable.limit < index * 8 + 7)
                 return 1;
-        return kvm_write_guest_virt(dtable.base + index*8, seg_desc, sizeof(*seg_desc), vcpu);
+        return kvm_write_guest_virt(dtable.base + index*8, seg_desc, sizeof(*seg_desc), vcpu, NULL);
+}
+
+static gpa_t get_tss_base_addr_write(struct kvm_vcpu *vcpu,
+                               struct desc_struct *seg_desc)
+{
+        u32 base_addr = get_desc_base(seg_desc);
+
+        return kvm_mmu_gva_to_gpa_write(vcpu, base_addr, NULL);
 }
 
-static gpa_t get_tss_base_addr(struct kvm_vcpu *vcpu,
+static gpa_t get_tss_base_addr_read(struct kvm_vcpu *vcpu,
                              struct desc_struct *seg_desc)
 {
         u32 base_addr = get_desc_base(seg_desc);
 
-        return vcpu->arch.mmu.gva_to_gpa(vcpu, base_addr);
+        return kvm_mmu_gva_to_gpa_read(vcpu, base_addr, NULL);
 }
 
 static u16 get_segment_selector(struct kvm_vcpu *vcpu, int seg)
@@ -4894,7 +4963,7 @@ static int kvm_task_switch_16(struct kvm_vcpu *vcpu, u16 tss_selector,
                             sizeof tss_segment_16))
                 goto out;
 
-        if (kvm_read_guest(vcpu->kvm, get_tss_base_addr(vcpu, nseg_desc),
+        if (kvm_read_guest(vcpu->kvm, get_tss_base_addr_read(vcpu, nseg_desc),
                            &tss_segment_16, sizeof tss_segment_16))
                 goto out;
 
@@ -4902,7 +4971,7 @@ static int kvm_task_switch_16(struct kvm_vcpu *vcpu, u16 tss_selector,
                 tss_segment_16.prev_task_link = old_tss_sel;
 
                 if (kvm_write_guest(vcpu->kvm,
-                                    get_tss_base_addr(vcpu, nseg_desc),
+                                    get_tss_base_addr_write(vcpu, nseg_desc),
                                     &tss_segment_16.prev_task_link,
                                     sizeof tss_segment_16.prev_task_link))
                         goto out;
@@ -4933,7 +5002,7 @@ static int kvm_task_switch_32(struct kvm_vcpu *vcpu, u16 tss_selector,
                             sizeof tss_segment_32))
                 goto out;
 
-        if (kvm_read_guest(vcpu->kvm, get_tss_base_addr(vcpu, nseg_desc),
+        if (kvm_read_guest(vcpu->kvm, get_tss_base_addr_read(vcpu, nseg_desc),
                            &tss_segment_32, sizeof tss_segment_32))
                 goto out;
 
@@ -4941,7 +5010,7 @@ static int kvm_task_switch_32(struct kvm_vcpu *vcpu, u16 tss_selector,
                 tss_segment_32.prev_task_link = old_tss_sel;
 
                 if (kvm_write_guest(vcpu->kvm,
-                                    get_tss_base_addr(vcpu, nseg_desc),
+                                    get_tss_base_addr_write(vcpu, nseg_desc),
                                     &tss_segment_32.prev_task_link,
                                     sizeof tss_segment_32.prev_task_link))
                         goto out;
@@ -4964,7 +5033,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
         u32 old_tss_base = get_segment_base(vcpu, VCPU_SREG_TR);
         u16 old_tss_sel = get_segment_selector(vcpu, VCPU_SREG_TR);
 
-        old_tss_base = vcpu->arch.mmu.gva_to_gpa(vcpu, old_tss_base);
+        old_tss_base = kvm_mmu_gva_to_gpa_write(vcpu, old_tss_base, NULL);
 
         /* FIXME: Handle errors. Failure to read either TSS or their
          * descriptors should generate a pagefault.
@@ -5199,7 +5268,7 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
 
         vcpu_load(vcpu);
         idx = srcu_read_lock(&vcpu->kvm->srcu);
-        gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, vaddr);
+        gpa = kvm_mmu_gva_to_gpa_system(vcpu, vaddr, NULL);
         srcu_read_unlock(&vcpu->kvm->srcu, idx);
         tr->physical_address = gpa;
         tr->valid = gpa != UNMAPPED_GVA;