[Qemu-devel] [PATCH for-1.4 v2] target-i386: kvm: prevent buffer overflow if -cpu foo, [x]level is too big

[Igor Mammedov]

Stack corruption may occur if too big 'level' or 'xlevel' values passed
on command line with KVM enabled, due to limited size of cpuid_data
in kvm_arch_init_vcpu().

reproduces with:
 qemu -enable-kvm -cpu qemu64,level=4294967295
or
 qemu -enable-kvm -cpu qemu64,xlevel=4294967295

Check if there is space in cpuid_data before passing it to cpu_x86_cpuid()
or abort() if there is not space.

Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
  * v2:
    * use macro instead of const int max_cpuid_entries to fix build breakage
      in C99 mode. Suggested-By: Laszlo Ersek <ler...@redhat.com>
    * compare with array index instead of address of the last element
          Sugested-By: Marcelo Tosatti <mtosa...@redhat.com>

---
 target-i386/kvm.c |   25 ++++++++++++++++++++++++-
 1 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 3acff40..4ecb728 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -411,11 +411,12 @@ static void cpu_update_state(void *opaque, int running, 
RunState state)
     }
 }
 
+#define KVM_MAX_CPUID_ENTRIES  100
 int kvm_arch_init_vcpu(CPUState *cs)
 {
     struct {
         struct kvm_cpuid2 cpuid;
-        struct kvm_cpuid_entry2 entries[100];
+        struct kvm_cpuid_entry2 entries[KVM_MAX_CPUID_ENTRIES];
     } QEMU_PACKED cpuid_data;
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
@@ -502,6 +503,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
     cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
 
     for (i = 0; i <= limit; i++) {
+        if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+            fprintf(stderr, "unsupported level value: 0x%x\n", limit);
+            abort();
+        }
         c = &cpuid_data.entries[cpuid_i++];
 
         switch (i) {
@@ -516,6 +521,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
             times = c->eax & 0xff;
 
             for (j = 1; j < times; ++j) {
+                if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+                    fprintf(stderr, "cpuid_data is full, no space for "
+                            "cpuid(eax:2):eax & 0xf = 0x%x\n", times);
+                    abort();
+                }
                 c = &cpuid_data.entries[cpuid_i++];
                 c->function = i;
                 c->flags = KVM_CPUID_FLAG_STATEFUL_FUNC;
@@ -544,6 +554,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
                 if (i == 0xd && c->eax == 0) {
                     continue;
                 }
+                if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+                    fprintf(stderr, "cpuid_data is full, no space for "
+                            "cpuid(eax:0x%x,ecx:0x%x)\n", i, j);
+                    abort();
+                }
                 c = &cpuid_data.entries[cpuid_i++];
             }
             break;
@@ -557,6 +572,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
     cpu_x86_cpuid(env, 0x80000000, 0, &limit, &unused, &unused, &unused);
 
     for (i = 0x80000000; i <= limit; i++) {
+        if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+            fprintf(stderr, "unsupported xlevel value: 0x%x\n", limit);
+            abort();
+        }
         c = &cpuid_data.entries[cpuid_i++];
 
         c->function = i;
@@ -569,6 +588,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
         cpu_x86_cpuid(env, 0xC0000000, 0, &limit, &unused, &unused, &unused);
 
         for (i = 0xC0000000; i <= limit; i++) {
+            if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
+                fprintf(stderr, "unsupported xlevel2 value: 0x%x\n", limit);
+                abort();
+            }
             c = &cpuid_data.entries[cpuid_i++];
 
             c->function = i;
-- 
1.7.1