Merge tag 'rfds-for-linus-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 RFDS mitigation from Dave Hansen:
 "RFDS is a CPU vulnerability that may allow a malicious userspace to
  infer stale register values from kernel space. Kernel registers can
  have all kinds of secrets in them so the mitigation is basically to
  wait until the kernel is about to return to userspace and has user
  values in the registers. At that point there is little chance of
  kernel secrets ending up in the registers and the microarchitectural
  state can be cleared.

  This leverages some recent robustness fixes for the existing MDS
  vulnerability. Both MDS and RFDS use the VERW instruction for
  mitigation"

* tag 'rfds-for-linus-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  KVM/x86: Export RFDS_NO and RFDS_CLEAR to guests
  x86/rfds: Mitigate Register File Data Sampling (RFDS)
  Documentation/hw-vuln: Add documentation for RFDS
  x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 9f616d1868d9..ae5a20cf2f9c 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -75,6 +75,8 @@ extern ssize_t cpu_show_spec_rstack_overflow(struct device *dev,
 					     struct device_attribute *attr, char *buf);
 extern ssize_t cpu_show_gds(struct device *dev,
 			    struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_reg_file_data_sampling(struct device *dev,
+					       struct device_attribute *attr, char *buf);
 
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,