KVM: VMX: Ensure guest's SPEC_CTRL[63:32] is loaded on VM-Enter

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SPEC_CTRL is an MSR, i.e. a 64-bit value, but the assembly code that loads
the guest's value assumes bits 63:32 are always zero.  The bug is
_currently_ benign because neither KVM nor the kernel support setting any
of bits 63:32, but it's still a bug that needs to be fixed.

Note, the host's value is restored in C code and is unaffected.

Fixes: 07853adc29 ("KVM: VMX: Prevent RSB underflow before vmenter")
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://patch.msgid.link/20250820100007.356761-1-ubizjak@gmail.com
[sean: call out that only the guest's value is affected]
Signed-off-by: Sean Christopherson <seanjc@google.com>

...

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Uros Bizjak 2025-08-20 11:59:54 +02:00 • committed by Sean Christopherson

parent 1100e4910a

commit 32ed0bc2f0

1 changed files with 15 additions and 5 deletions

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arch/x86/kvm/vmx/vmenter.S

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