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| author | Paolo Bonzini <pbonzini@redhat.com> | 2022-03-18 16:23:47 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-03-20 20:38:52 +0100 |
| commit | 3ec5ad40081b14af28496198b4d08dbe13386790 (patch) | |
| tree | 316f10a515bdc38709a65fd0b0a08e182abb718c /target/i386/kvm | |
| parent | e2fb7d8aa218256793df99571d16f92074258447 (diff) | |
| download | qemu-3ec5ad40081b14af28496198b4d08dbe13386790.zip qemu-3ec5ad40081b14af28496198b4d08dbe13386790.tar.gz qemu-3ec5ad40081b14af28496198b4d08dbe13386790.tar.bz2 | |
target/i386: kvm: do not access uninitialized variable on older kernels
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>
Diffstat (limited to 'target/i386/kvm')
| -rw-r--r-- | target/i386/kvm/kvm.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index ef2c68a..06901c2 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) { |