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[PULL 1/2] target/i386: kvm: do not access uninitialized variable on old
From: |
Paolo Bonzini |
Subject: |
[PULL 1/2] target/i386: kvm: do not access uninitialized variable on older kernels |
Date: |
Mon, 21 Mar 2022 17:45:01 +0100 |
KVM support for AMX includes a new system attribute, KVM_X86_XCOMP_GUEST_SUPP.
Commit 19db68ca68 ("x86: Grant AMX permission for guest", 2022-03-15) however
did not fully consider the behavior on older kernels. First, it warns
too aggressively. Second, it invokes the KVM_GET_DEVICE_ATTR ioctl
unconditionally and then uses the "bitmask" variable, which remains
uninitialized if the ioctl fails. Third, kvm_ioctl returns -errno rather
than -1 on errors.
While at it, explain why the ioctl is needed and KVM_GET_SUPPORTED_CPUID
is not enough.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
target/i386/kvm/kvm.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index ef2c68a6f4..06901c2a43 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -411,6 +411,12 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s,
uint32_t function,
}
} else if (function == 0xd && index == 0 &&
(reg == R_EAX || reg == R_EDX)) {
+ /*
+ * The value returned by KVM_GET_SUPPORTED_CPUID does not include
+ * features that still have to be enabled with the arch_prctl
+ * system call. QEMU needs the full value, which is retrieved
+ * with KVM_GET_DEVICE_ATTR.
+ */
struct kvm_device_attr attr = {
.group = 0,
.attr = KVM_X86_XCOMP_GUEST_SUPP,
@@ -419,13 +425,16 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s,
uint32_t function,
bool sys_attr = kvm_check_extension(s, KVM_CAP_SYS_ATTRIBUTES);
if (!sys_attr) {
- warn_report("cannot get sys attribute capabilities %d", sys_attr);
+ return ret;
}
int rc = kvm_ioctl(s, KVM_GET_DEVICE_ATTR, &attr);
- if (rc == -1 && (errno == ENXIO || errno == EINVAL)) {
- warn_report("KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) "
- "error: %d", rc);
+ if (rc < 0) {
+ if (rc != -ENXIO) {
+ warn_report("KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) "
+ "error: %d", rc);
+ }
+ return ret;
}
ret = (reg == R_EAX) ? bitmask : bitmask >> 32;
} else if (function == 0x80000001 && reg == R_ECX) {
--
2.35.1