Merge tag 'vmscape-for-linus-20250904' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull vmescape mitigation fixes from Dave Hansen:
"Mitigate vmscape issue with indirect branch predict

Merge tag 'vmscape-for-linus-20250904' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull vmescape mitigation fixes from Dave Hansen:
"Mitigate vmscape issue with indirect branch predictor flushes.

vmscape is a vulnerability that essentially takes Spectre-v2 and
attacks host userspace from a guest. It particularly affects
hypervisors like QEMU.

Even if a hypervisor may not have any sensitive data like disk
encryption keys, guest-userspace may be able to attack the
guest-kernel using the hypervisor as a confused deputy.

There are many ways to mitigate vmscape using the existing Spectre-v2
defenses like IBRS variants or the IBPB flushes. This series focuses
solely on IBPB because it works universally across vendors and all
vulnerable processors. Further work doing vendor and model-specific
optimizations can build on top of this if needed / wanted.

Do the normal issue mitigation dance:

- Add the CPU bug boilerplate

- Add a list of vulnerable CPUs

- Use IBPB to flush the branch predictors after running guests"

* tag 'vmscape-for-linus-20250904' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/vmscape: Add old Intel CPUs to affected list
x86/vmscape: Warn when STIBP is disabled with SMT
x86/bugs: Move cpu_bugs_smt_update() down
x86/vmscape: Enable the mitigation
x86/vmscape: Add conditional IBPB mitigation
x86/vmscape: Enumerate VMSCAPE bug
Documentation/hw-vuln: Add VMSCAPE documentation

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Documentation/hw-vuln: Add VMSCAPE documentation

VMSCAPE is a vulnerability that may allow a guest to influence the branch
prediction in host userspace, particularly affecting hypervisors like QEMU.

Documentation/hw-vuln: Add VMSCAPE documentation

VMSCAPE is a vulnerability that may allow a guest to influence the branch
prediction in host userspace, particularly affecting hypervisors like QEMU.

Add the documentation.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>

show more ...