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119 lines
5.0 KiB
119 lines
5.0 KiB
From 44cbd79562ed55a8b0f2e5b5dc708265568ed9f8 Mon Sep 17 00:00:00 2001
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From: Noah Meyerhans <nmeyerha@amazon.com>
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Date: Fri, 30 Apr 2021 09:30:52 -0700
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Subject: [PATCH] Use BIOS characteristics to distinguish EC2 bare-metal from
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VMs
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DMI vendor information fields do not provide enough information for us to
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distinguish between Amazon EC2 virtual machines and bare-metal instances.
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SMBIOS provides a BIOS Information
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table (https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.4.0.pdf
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Ch. 7) that provides a field to indicate that the current machine is a virtual
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machine. On EC2 virtual machine instances, this field is set, while bare-metal
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instances leave this unset, so we inspect the field via the kernel's
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/sys/firemware/dmi/entries interface.
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Fixes #18929
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(cherry picked from commit ce35037928f4c4c931088256853f07804ec7d235)
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Related: #2117948
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---
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src/basic/virt.c | 65 +++++++++++++++++++++++++++++++++++++++++++++---
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1 file changed, 61 insertions(+), 4 deletions(-)
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diff --git a/src/basic/virt.c b/src/basic/virt.c
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index 6e4c702051..00d1c894e6 100644
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--- a/src/basic/virt.c
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+++ b/src/basic/virt.c
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@@ -22,6 +22,12 @@
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#include "string-util.h"
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#include "virt.h"
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+enum {
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+ SMBIOS_VM_BIT_SET,
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+ SMBIOS_VM_BIT_UNSET,
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+ SMBIOS_VM_BIT_UNKNOWN,
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+};
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+
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static const char *const vm_table[_VIRTUALIZATION_MAX] = {
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[VIRTUALIZATION_XEN] = "XenVMMXenVMM",
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[VIRTUALIZATION_KVM] = "KVMKVMKVM",
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@@ -131,9 +137,8 @@ static int detect_vm_device_tree(void) {
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#endif
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}
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-static int detect_vm_dmi(void) {
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#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__aarch64__)
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-
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+static int detect_vm_dmi_vendor(void) {
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static const char *const dmi_vendors[] = {
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"/sys/class/dmi/id/product_name", /* Test this before sys_vendor to detect KVM over QEMU */
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"/sys/class/dmi/id/sys_vendor",
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@@ -179,11 +184,63 @@ static int detect_vm_dmi(void) {
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return dmi_vendor_table[j].id;
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}
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}
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-#endif
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+ return VIRTUALIZATION_NONE;
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+}
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+
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+static int detect_vm_smbios(void) {
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+ /* The SMBIOS BIOS Charateristics Extension Byte 2 (Section 2.1.2.2 of
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+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.4.0.pdf), specifies that
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+ * the 4th bit being set indicates a VM. The BIOS Characteristics table is exposed via the kernel in
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+ * /sys/firmware/dmi/entries/0-0. Note that in the general case, this bit being unset should not
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+ * imply that the system is running on bare-metal. For example, QEMU 3.1.0 (with or without KVM)
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+ * with SeaBIOS does not set this bit. */
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+ _cleanup_free_ char *s = NULL;
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+ size_t readsize;
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+ int r;
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+
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+ r = read_full_virtual_file("/sys/firmware/dmi/entries/0-0/raw", &s, &readsize);
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+ if (r < 0) {
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+ log_debug_errno(r, "Unable to read /sys/firmware/dmi/entries/0-0/raw, ignoring: %m");
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+ return SMBIOS_VM_BIT_UNKNOWN;
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+ }
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+ if (readsize < 20 || s[1] < 20) {
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+ /* The spec indicates that byte 1 contains the size of the table, 0x12 + the number of
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+ * extension bytes. The data we're interested in is in extension byte 2, which would be at
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+ * 0x13. If we didn't read that much data, or if the BIOS indicates that we don't have that
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+ * much data, we don't infer anything from the SMBIOS. */
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+ log_debug("Only read %zu bytes from /sys/firmware/dmi/entries/0-0/raw (expected 20)", readsize);
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+ return SMBIOS_VM_BIT_UNKNOWN;
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+ }
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- log_debug("No virtualization found in DMI");
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+ uint8_t byte = (uint8_t) s[19];
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+ if (byte & (1U<<4)) {
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+ log_debug("DMI BIOS Extension table indicates virtualization");
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+ return SMBIOS_VM_BIT_SET;
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+ }
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+ log_debug("DMI BIOS Extension table does not indicate virtualization");
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+ return SMBIOS_VM_BIT_UNSET;
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+}
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+#endif /* defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) */
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+
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+static int detect_vm_dmi(void) {
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+#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__aarch64__)
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+
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+ int r;
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+ r = detect_vm_dmi_vendor();
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+ /* The DMI vendor tables in /sys/class/dmi/id don't help us distinguish between Amazon EC2
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+ * virtual machines and bare-metal instances, so we need to look at SMBIOS. */
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+ if (r == VIRTUALIZATION_AMAZON && detect_vm_smbios() == SMBIOS_VM_BIT_UNSET)
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+ return VIRTUALIZATION_NONE;
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+
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+ /* If we haven't identified a VM, but the firmware indicates that there is one, indicate as much. We
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+ * have no further information about what it is. */
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+ if (r == VIRTUALIZATION_NONE && detect_vm_smbios() == SMBIOS_VM_BIT_SET)
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+ return VIRTUALIZATION_VM_OTHER;
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+ return r;
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+#else
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return VIRTUALIZATION_NONE;
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+#endif
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}
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static int detect_vm_xen(void) {
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