CVE-2025-38508 — x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

When using Secure TSC, the GUEST_TSC_FREQ MSR reports a frequency based on the nominal P0 frequency, which deviates slightly (typically ~0.2%) from the actual mean TSC frequency due to clocking parameters.

Over extended VM uptime, this discrepancy accumulates, causing clock skew between the hypervisor and a SEV-SNP VM, leading to early timer interrupts as perceived by the guest.

The guest kernel relies on the reported nominal frequency for TSC-based timekeeping, while the actual frequency set during SNP_LAUNCH_START may differ. This mismatch results in inaccurate time calculations, causing the guest to perceive hrtimers as firing earlier than expected.

Utilize the TSC_FACTOR from the SEV firmware's secrets page (see "Secrets Page Format" in the SNP Firmware ABI Specification) to calculate the mean TSC frequency, ensuring accurate timekeeping and mitigating clock skew in SEV-SNP VMs.

Use early_ioremap_encrypted() to map the secrets page as ioremap_encrypted() uses kmalloc() which is not available during early TSC initialization and causes a panic.

[ bp: Drop the silly dummy var: https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local ]

USN-7879-1 — linux, linux-aws, linux-gcp, linux-hwe-6.14, linux-oracle, linux-realtime vulnerabilities

Affected: Ubuntu:24.04:LTS: linux-hwe-6.14

It was discovered that improper initialization of CPU cache memory could allow a local attacker with hypervisor access to overwrite SEV-SNP guest memory resulting in loss of data integrity. (CVE-2024-36331)

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - PowerPC architecture; - S390 architecture; - x86 architecture; - Network block device driver; - Character device driver; - Clock framework and drivers; - Data acquisition framework and drivers; - Hardware crypto device drivers; - Device frequency scaling framework; - DMA engine subsystem; - EDAC drivers; - GPU drivers; - HID subsystem; - Hardware monitoring drivers; - I2C subsystem; - IIO subsystem; - IIO ADC drivers; - InfiniBand drivers; - Input Device core drivers; - Multiple devices driver; - Media drivers; - Network drivers; - Mellanox network drivers; - PCI subsystem; - PHY drivers; - Pin controllers subsystem; - x86 platform drivers; - Power supply drivers; - Powercap sysfs driver; - Voltage and Current Regulator drivers; - S/390 drivers; - ASPEED SoC drivers; - SPI subsystem; - small TFT LCD display modules; - Media staging drivers; - USB Gadget drivers; - vDPA drivers; - VFIO drivers; - Framebuffer layer; - Xen hypervisor drivers; - BTRFS file system; - Ceph distributed file sy…

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CVE-2025-38508 — x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

USN-7879-1 — linux, linux-aws, linux-gcp, linux-hwe-6.14, linux-oracle, linux-realtime vulnerabilities