CVE-2018-5683

The vga_draw_text function in Qemu allows local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation.

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).

These non-security issues were fixed:

• bsc#1067317: pass cache=writeback|unsafe|directsync to qemu depending on the libxl disk settings
• bsc#1051729: Prevent invalid symlinks after install of SLES 12 SP2
• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100 seconds. If many domUs shutdown in parallel the backends couldn't keep up
• bsc#1027519: Added several upstream patches

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).

These non-security issues were fixed:

• bsc#1051729: Prevent invalid symlinks after install of SLES 12 SP2
• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100 seconds. If many domUs shutdown in parallel the backends couldn't keep up
• bsc#1027519: Added several upstream patches

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• Added missing intermediate preemption checks for guest requesting removal of memory. This allowed malicious guest administrator to cause denial of service due to the high cost of this operation (bsc#1080635).
• Because of XEN not returning the proper error messages when transitioning grant tables from v2 to v1 a malicious guest was able to cause DoS or potentially allowed for privilege escalation as well as information leaks (bsc#1080662).

This non-security issue was fixed:

• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100 seconds. If many domUs shutdown in parallel the backends couldn't keep up

• Upstream patches from Jan (bsc#1027519)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• Added missing intermediate preemption checks for guest requesting removal of memory. This allowed malicious guest administrator to cause denial of service due to the high cost of this operation (bsc#1080635).
• Because of XEN not returning the proper error messages when transitioning grant tables from v2 to v1 a malicious guest was able to cause DoS or potentially allowed for privilege escalation as well as information leaks (bsc#1080662).

This non-security issue was fixed:

• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100 seconds. If many domUs shutdown in parallel the backends couldn't keep up

This update for xen fixes several issues.

This new feature was included:

• add script and sysv service to watch for vcpu online/offline events in a HVM domU

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• Added missing intermediate preemption checks for guest requesting removal of memory. This allowed malicious guest administrator to cause denial of service due to the high cost of this operation (bsc#1080635).
• Because of XEN not returning the proper error messages when transitioning grant tables from v2 to v1 a malicious guest was able to cause DoS or potentially allowed for privilege escalation as well as information leaks (bsc#1080662).

These non-security issues were fixed:

• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100 seconds. If many domUs shutdown in parallel the backends couldn't keep up
• bsc#1031382: Prevent VMs from crashing when migrating between dom0 hosts in case read() returns zero on the receiver side.

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks via side effects of speculative execution, aka 'Spectre' and 'Meltdown' attacks (bsc#1074562, bsc#1068032)
• CVE-2018-5683: The vga_draw_text function allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch (bsc#1076180).
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P (bsc#1070163).
• Added missing intermediate preemption checks for guest requesting removal of memory. This allowed malicious guest administrator to cause denial of service due to the high cost of this operation (bsc#1080635).
• Because of XEN not returning the proper error messages when transitioning grant tables from v2 to v1 a malicious guest was able to cause DoS or potentially allowed for privilege escalation as well as information leaks (bsc#1080662).
• CVE-2017-5898: The CCID Card device emulator support was vulnerable to an integer overflow flaw allowing a privileged user to crash the Qemu process on the host resulting in DoS (bsc#1024307)
• Unprivileged domains could have issued well-timed writes to xenstore which conflict with transactions to stall progress of the control domain or driver domain, possibly leading to DoS (bsc#1030144, XSA-206).

This update for qemu fixes the following issues:

This update has the next round of Spectre v2 related patches, which now integrate with corresponding changes in libvirt. (CVE-2017-5715 bsc#1068032)

The January 2018 release of qemu initially addressed the Spectre v2 vulnerability for KVM guests by exposing the spec-ctrl feature for all x86 vcpu types, which was the quick and dirty approach, but not the proper solution.

We replaced our initial patch by the patches from upstream.

This update defines spec_ctrl and ibpb cpu feature flags as well as new cpu models which are clones of existing models with either -IBRS or -IBPB added to the end of the model name. These new vcpu models explicitly include the new feature(s), whereas the feature flags can be added to the cpu parameter as with other features. In short, for continued Spectre v2 protection, ensure that either the appropriate cpu feature flag is added to the QEMU command-line, or one of the new cpu models is used.

Although migration from older versions is supported, the new cpu features won't be properly exposed to the guest until it is restarted with the cpu features explicitly added. A reboot is insufficient.

A warning patch is added which attempts to detect a migration from a qemu version which had the quick and dirty fix (it only detects certain cases, but hopefully is helpful.) For additional information on Spectre v2 as it relates to QEMU, see: https://www.qemu.org/2018/02/14/qemu-2-11-1-and-spectre-update/

A patch is added to continue to detect Spectre v2 mitigation features (as shown by cpuid), and if found provide that feature to guests, even if running on older KVM (kernel) versions which do not yet expose that feature to QEMU. (bsc#1082276)

These two patches will be removed when we can reasonably assume everyone is running with the appropriate updates.

Spectre fixes for IBM Z Series were included by providing more hw features to guests (bsc#1076813)

Also security fixes for the following CVE issues are included:

• CVE-2017-17381: The Virtio Vring implementation in QEMU allowed local OS guest users to cause a denial of service (divide-by-zero error and QEMU process crash) by unsetting vring alignment while updating Virtio rings. (bsc#1071228)
• CVE-2017-16845: The PS2 driver in Qemu did not validate 'rptr' and 'count' values during guest migration, leading to out-of-bounds access. (bsc#1068613)
• CVE-2017-15119: The Network Block Device (NBD) server in Quick Emulator (QEMU), was vulnerable to a denial of service issue. It could occur if a client sent large option requests, making the server waste CPU time on reading up to 4GB per request. A client could use this flaw to keep the NBD server from serving other requests, resulting in DoS. (bsc#1070144)
• CVE-2017-18043: Integer overflow in the macro ROUND_UP (n, d) in Quick Emulator (Qemu) allowed a user to cause a denial of service (Qemu process crash). (bsc#1076775)
• CVE-2018-5683: The VGA driver in Qemu allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation. (bsc#1076114)
• CVE-2018-7550: The multiboot functionality in Quick Emulator (aka QEMU) allowed local guest OS users to execute arbitrary code on the QEMU host via an out-of-bounds read or write memory access. (bsc#1083291)
• CVE-2017-15124: VNC server implementation in Quick Emulator (QEMU) was found to be vulnerable to an unbounded memory allocation issue, as it did not throttle the framebuffer updates sent to its client. If the client did not consume these updates, VNC server allocates growing memory to hold onto this data. A malicious remote VNC client could use this flaw to cause DoS to the server host. (bsc#1073489)

Additional bugs fixed:

• Fix pcihp for 1.6 and older machine types (bsc#1074572)
• Fix packaging dependencies (coreutils) for qemu-ksm package (bsc#1040202)

This update for qemu fixes the following issues:

This update has the next round of Spectre v2 related patches, which now integrate with corresponding changes in libvirt. (CVE-2017-5715 bsc#1068032)

The January 2018 release of qemu initially addressed the Spectre v2 vulnerability for KVM guests by exposing the spec-ctrl feature for all x86 vcpu types, which was the quick and dirty approach, but not the proper solution.

We replaced our initial patch by the patches from upstream.

This update defines spec_ctrl and ibpb cpu feature flags as well as new cpu models which are clones of existing models with either -IBRS or -IBPB added to the end of the model name. These new vcpu models explicitly include the new feature(s), whereas the feature flags can be added to the cpu parameter as with other features. In short, for continued Spectre v2 protection, ensure that either the appropriate cpu feature flag is added to the QEMU command-line, or one of the new cpu models is used.

Although migration from older versions is supported, the new cpu features won't be properly exposed to the guest until it is restarted with the cpu features explicitly added. A reboot is insufficient.

A warning patch is added which attempts to detect a migration from a qemu version which had the quick and dirty fix (it only detects certain cases, but hopefully is helpful.) For additional information on Spectre v2 as it relates to QEMU, see: https://www.qemu.org/2018/02/14/qemu-2-11-1-and-spectre-update/

A patch is added to continue to detect Spectre v2 mitigation features (as shown by cpuid), and if found provide that feature to guests, even if running on older KVM (kernel) versions which do not yet expose that feature to QEMU. (bsc#1082276)

These two patches will be removed when we can reasonably assume everyone is running with the appropriate updates.

Also security fixes for the following CVE issues are included:

• CVE-2017-15119: The Network Block Device (NBD) server in Quick Emulator (QEMU), was vulnerable to a denial of service issue. It could occur if a client sent large option requests, making the server waste CPU time on reading up to 4GB per request. A client could use this flaw to keep the NBD server from serving other requests, resulting in DoS. (bsc#1070144)
• CVE-2017-15124: VNC server implementation in Quick Emulator (QEMU) was found to be vulnerable to an unbounded memory allocation issue, as it did not throttle the framebuffer updates sent to its client. If the client did not consume these updates, VNC server allocates growing memory to hold onto this data. A malicious remote VNC client could use this flaw to cause DoS to the server host. (bsc#1073489)
• CVE-2017-16845: The PS2 driver in Qemu did not validate 'rptr' and 'count' values during guest migration, leading to out-of-bounds access. (bsc#1068613)
• CVE-2017-17381: The Virtio Vring implementation in QEMU allowed local OS guest users to cause a denial of service (divide-by-zero error and QEMU process crash) by unsetting vring alignment while updating Virtio rings. (bsc#1071228)
• CVE-2017-18030: A problem in the Cirrus driver in Qemu allowed local OS guest privileged users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors related to negative pitch. (bsc#1076179)
• CVE-2017-18043: Integer overflow in the macro ROUND_UP (n, d) in Quick Emulator (Qemu) allowed a user to cause a denial of service (Qemu process crash). (bsc#1076775)
• CVE-2018-5683: The VGA driver in Qemu allowed local OS guest privileged users to cause a denial of service (out-of-bounds read and QEMU process crash) by leveraging improper memory address validation. (bsc#1076114)
• CVE-2018-7550: The multiboot functionality in Quick Emulator (aka QEMU) allowed local guest OS users to execute arbitrary code on the QEMU host via an out-of-bounds read or write memory access. (bsc#1083291)

Also the following bugs were fixed:

• Eliminate bogus use of CPUID_7_0_EDX_PRED_CMD…

This update for kvm fixes the following issues:

• This update has the next round of Spectre v2 related patches, which now integrates with corresponding changes in libvirt. A January 2018 release of qemu initially addressed the Spectre v2 vulnerability for KVM guests by exposing the spec-ctrl feature for all x86 vcpu types, which was the quick and dirty approach, but not the proper solution. We remove that initial patch and now rely on patches from upstream. This update defines spec_ctrl and ibpb cpu feature flags as well as new cpu models which are clones of existing models with either -IBRS or -IBPB added to the end of the model name. These new vcpu models explicitly include the new feature(s), whereas the feature flags can be added to the cpu parameter as with other features. In short, for continued Spectre v2 protection, ensure that either the appropriate cpu feature flag is added to the QEMU command-line, or one of the new cpu models is used. Although migration from older versions is supported, the new cpu features won't be properly exposed to the guest until it is restarted with the cpu features explicitly added. A reboot is insufficient.

• A warning patch is added which attempts to detect a migration from a qemu version which had the quick and dirty fix (it only detects certain cases, but hopefully is helpful.) For additional information on Spectre v2 as it relates to QEMU, see: https://www.qemu.org/2018/02/14/qemu-2-11-1-and-spectre-update/ (CVE-2017-5715 bsc#1068032)

• A patch is added to continue to detect Spectre v2 mitigation features (as shown by cpuid), and if found provide that feature to guests, even if running on older KVM (kernel) versions which do not yet expose that feature to QEMU. (bsc#1082276) These two patches will be removed when we can reasonably assume everyone is running with the appropriate updates.

• Security fixes for the following CVE issues: (bsc#1076114 CVE-2018-5683) (bsc#1083291 CVE-2018-7550)

• This patch is already included, add here for CVE track (bsc#1076179 CVE-2017-18030)

• Toolchain changes have cause the built size of pxe-virtio.rom to exceed 64K. Tweak rarely used strings in code to reduce size of the binary so it fits again.

• Eliminate bogus use of CPUID_7_0_EDX_PRED_CMD which we've carried since the initial Spectre v2 patch was added. EDX bit 27 of CPUID Leaf 07H, Sub-leaf 0 provides status on STIBP, and not the PRED_CMD MSR. Exposing the STIBP CPUID feature bit to the guest is wrong in general, since the VM doesn't directly control the scheduling of physical hyperthreads. This is left strictly to the L0 hypervisor.

This update for kvm fixes the following issues:

This update has the next round of Spectre v2 related patches, which now integrates with corresponding changes in libvirt. A January 2018 release of qemu initially addressed the Spectre v2 vulnerability for KVM guests by exposing the spec-ctrl feature for all x86 vcpu types, which was the quick and dirty approach, but not the proper solution. We remove that initial patch and now rely on patches from upstream. This update defines spec_ctrl and ibpb cpu feature flags as well as new cpu models which are clones of existing models with either -IBRS or -IBPB added to the end of the model name. These new vcpu models explicitly include the new feature(s), whereas the feature flags can be added to the cpu parameter as with other features. In short, for continued Spectre v2 protection, ensure that either the appropriate cpu feature flag is added to the QEMU command-line, or one of the new cpu models is used. Although migration from older versions is supported, the new cpu features won't be properly exposed to the guest until it is restarted with the cpu features explicitly added. A reboot is insufficient.

A warning patch is added which attempts to detect a migration from a qemu version which had the quick and dirty fix (it only detects certain cases, but hopefully is helpful.)

For additional information on Spectre v2 as it relates to QEMU, see: https://www.qemu.org/2018/02/14/qemu-2-11-1-and-spectre-update/

(CVE-2017-5715 bsc#1068032)

A patch is added to continue to detect Spectre v2 mitigation features (as shown by cpuid), and if found provide that feature to guests, even if running on older KVM (kernel) versions which do not yet expose that feature to QEMU. (bsc#1082276)

Additional security fixes:

• CVE-2018-5683: An out-of-bounds read in vga_draw_text routine was fixed which could lead to crashes or information leakage. (bsc#1076114)

• CVE-2018-7550: multiboot OOB access while loading kernel image was fixed that could lead to crashes (bsc#1083291)

• CVE-2017-18030: An out-of-bounds access in cirrus_invalidate_region routine could lead to crashes or information leakage (bsc#1076179)

• Eliminate bogus use of CPUID_7_0_EDX_PRED_CMD which we've carried since the initial Spectre v2 patch was added. EDX bit 27 of CPUID Leaf 07H, Sub-leaf 0 provides status on STIBP, and not the PRED_CMD MSR. Exposing the STIBP CPUID feature bit to the guest is wrong in general, since the VM doesn't directly control the scheduling of physical hyperthreads. This is left strictly to the L0 hypervisor.

It was discovered that QEMU incorrectly handled guest ram. A privileged attacker inside the guest could use this issue to cause QEMU to crash, resulting in a denial of service. This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. (CVE-2017-11334)

David Buchanan discovered that QEMU incorrectly handled the VGA device. A privileged attacker inside the guest could use this issue to cause QEMU to crash, resulting in a denial of service. This issue was only addressed in Ubuntu 17.10. (CVE-2017-13672)

Thomas Garnier discovered that QEMU incorrectly handled multiboot. An attacker could use this issue to cause QEMU to crash, resulting in a denial of service, or possibly execute arbitrary code on the host. In the default installation, when QEMU is used with libvirt, attackers would be isolated by the libvirt AppArmor profile. This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. (CVE-2017-14167)

Tuomas Tynkkynen discovered that QEMU incorrectly handled VirtFS directory sharing. An attacker could use this issue to obtain sensitive information from host memory. (CVE-2017-15038)

Eric Blake discovered that QEMU incorrectly handled memory in the NBD server. An attacker could use this issue to cause the NBD server to crash, resulting in a denial of service. This issue only affected Ubuntu 17.10. (CVE-2017-15118)

Eric Blake discovered that QEMU incorrectly handled certain options to the NBD server. An attacker could use this issue to cause the NBD server to crash, resulting in a denial of service. This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. (CVE-2017-15119)

Daniel Berrange discovered that QEMU incorrectly handled the VNC server. A remote attacker could possibly use this issue to consume memory, resulting in a denial of service. This issue was only addressed in Ubuntu 17.10. (CVE-2017-15124)

Carl Brassey discovered that QEMU incorrectly handled certain websockets. A remote attacker could possibly use this issue to consume memory, resulting in a denial of service. This issue only affected Ubuntu 17.10. (CVE-2017-15268)

Guoxiang Niu discovered that QEMU incorrectly handled the Cirrus VGA device. A privileged attacker inside the guest could use this issue to cause QEMU to crash, resulting in a denial of service. (CVE-2017-15289)

Cyrille Chatras discovered that QEMU incorrectly handled certain PS2 values during migration. An attacker could possibly use this issue to cause QEMU to crash, resulting in a denial of service, or possibly execute arbitrary code. This issue only affected Ubuntu 16.04 LTS and Ubuntu 17.10. (CVE-2017-16845)

It was discovered that QEMU incorrectly handled the Virtio Vring implementation. An attacker could possibly use this issue to cause QEMU to crash, resulting in a denial of service. This issue only affected Ubuntu 16.04 LTS and Ubuntu 17.10. (CVE-2017-17381)

Eric Blake discovered that QEMU incorrectly handled certain rounding operations. An attacker could possibly use this issue to cause QEMU to crash, resulting in a denial of service. This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. (CVE-2017-18043)

Jiang Xin and Lin ZheCheng discovered that QEMU incorrectly handled the VGA device. A privileged attacker inside the guest could use this issue to cause QEMU to crash, resulting in a denial of service. (CVE-2018-5683)