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virt: Fix Xen Dom0 detection logic to no longer report as VM

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Fixes regression introduced in 599be274c1

Moving the Xen check before the CPUID check, in order to handle the case where
a Xen domain is nested within a hypervisor which can be detected by via the
CPUID check, had an unintended consequence of causing Dom0 to report as a Xen
VM when it is not nested.

This patch stops further checks once it has been determined that Dom0 is not
nested within another hypervisor, meaning that the non-nested case matches its
previous logic (where it does not report as a VM).

Also, tidy the conditionals for the Xen and UML checks by removing handling of
a VIRTUALIZATION_VM_OTHER result, which has no code path.

Fixes #22511
This commit is contained in:
Richard Neill 2022-02-02 18:18:46 +00:00 committed by Lennart Poettering
parent bde335f21f
commit ea583ed5a3
1 changed files with 21 additions and 19 deletions
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40
src/basic/virt.c
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@ -331,22 +331,13 @@ static int detect_vm_xen_dom0(void) {
}
static int detect_vm_xen(void) {
int r;
/* The presence of /proc/xen indicates some form of a Xen domain */
/* The presence of /proc/xen indicates some form of a Xen domain
The check for Dom0 is handled outside this function */
if (access("/proc/xen", F_OK) < 0) {
log_debug("Virtualization XEN not found, /proc/xen does not exist");
return VIRTUALIZATION_NONE;
}
log_debug("Virtualization XEN found (/proc/xen exists)");
/* Ignore the Xen hypervisor if we are in Dom0 */
r = detect_vm_xen_dom0();
if (r < 0)
return r;
if (r > 0)
return VIRTUALIZATION_NONE;
return VIRTUALIZATION_XEN;
}
@ -434,7 +425,7 @@ static int detect_vm_zvm(void) {
int detect_vm(void) {
static thread_local int cached_found = _VIRTUALIZATION_INVALID;
bool other = false;
int r, dmi;
int r, dmi, xen_dom0 = 0;
if (cached_found >= 0)
return cached_found;
@ -461,19 +452,26 @@ int detect_vm(void) {
r = detect_vm_uml();
if (r < 0)
return r;
if (r == VIRTUALIZATION_VM_OTHER)
other = true;
else if (r != VIRTUALIZATION_NONE)
if (r != VIRTUALIZATION_NONE)
goto finish;
/* Detect Xen */
r = detect_vm_xen();
if (r < 0)
return r;
if (r == VIRTUALIZATION_VM_OTHER)
other = true;
else if (r != VIRTUALIZATION_NONE)
goto finish;
if (r == VIRTUALIZATION_XEN) {
/* If we are Dom0, then we expect to not report as a VM. However, as we might be nested
* inside another hypervisor which can be detected via the CPUID check, wait to report this
* until after the CPUID check. */
xen_dom0 = detect_vm_xen_dom0();
if (xen_dom0 < 0)
return xen_dom0;
if (xen_dom0 == 0)
goto finish;
r = VIRTUALIZATION_NONE;
} else if (r != VIRTUALIZATION_NONE)
assert_not_reached();
/* Detect from CPUID */
r = detect_vm_cpuid();
@ -484,6 +482,10 @@ int detect_vm(void) {
else if (r != VIRTUALIZATION_NONE)
goto finish;
/* If we are in Dom0 and have not yet finished, finish with the result of detect_vm_cpuid */
if (xen_dom0 > 0)
goto finish;
/* Now, let's get back to DMI */
if (dmi < 0)
return dmi;