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author | Wanpeng Li <wanpeng.li@hotmail.com> | 2017-06-08 01:22:07 -0700 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-06-08 15:38:21 +0200 |
commit | a3641631d14571242eec0d30c9faa786cbf52d44 (patch) | |
tree | 72fb84145a6b3e7d2e4c1cbbc228d3e765feef76 /arch/x86 | |
parent | 38a4f43d5698daec601f4c5652ec287e594faf84 (diff) | |
download | linux-a3641631d14571242eec0d30c9faa786cbf52d44.tar.gz linux-a3641631d14571242eec0d30c9faa786cbf52d44.tar.bz2 linux-a3641631d14571242eec0d30c9faa786cbf52d44.zip |
KVM: cpuid: Fix read/write out-of-bounds vulnerability in cpuid emulation
If "i" is the last element in the vcpu->arch.cpuid_entries[] array, it
potentially can be exploited the vulnerability. this will out-of-bounds
read and write. Luckily, the effect is small:
/* when no next entry is found, the current entry[i] is reselected */
for (j = i + 1; ; j = (j + 1) % nent) {
struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
if (ej->function == e->function) {
It reads ej->maxphyaddr, which is user controlled. However...
ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
After cpuid_entries there is
int maxphyaddr;
struct x86_emulate_ctxt emulate_ctxt; /* 16-byte aligned */
So we have:
- cpuid_entries at offset 1B50 (6992)
- maxphyaddr at offset 27D0 (6992 + 3200 = 10192)
- padding at 27D4...27DF
- emulate_ctxt at 27E0
And it writes in the padding. Pfew, writing the ops field of emulate_ctxt
would have been much worse.
This patch fixes it by modding the index to avoid the out-of-bounds
access. Worst case, i == j and ej->function == e->function,
the loop can bail out.
Reported-by: Moguofang <moguofang@huawei.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Guofang Mo <moguofang@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/kvm/cpuid.c | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index a181ae76c71c..59ca2eea522c 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -780,18 +780,20 @@ out: static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i) { struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i]; - int j, nent = vcpu->arch.cpuid_nent; + struct kvm_cpuid_entry2 *ej; + int j = i; + int nent = vcpu->arch.cpuid_nent; e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT; /* when no next entry is found, the current entry[i] is reselected */ - for (j = i + 1; ; j = (j + 1) % nent) { - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j]; - if (ej->function == e->function) { - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; - return j; - } - } - return 0; /* silence gcc, even though control never reaches here */ + do { + j = (j + 1) % nent; + ej = &vcpu->arch.cpuid_entries[j]; + } while (ej->function != e->function); + + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; + + return j; } /* find an entry with matching function, matching index (if needed), and that |