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Peter Anvin" Subject: [PATCH] KVM: VMX: Fix SPEC_CTRL handling Date: Wed, 20 Aug 2025 11:59:54 +0200 Message-ID: <20250820100007.356761-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" SPEC_CTRL is an MSR, i.e. a 64-bit value, but the assembly code 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 Fixes: 07853adc29a0 ("KVM: VMX: Prevent RSB underflow before vmenter") Suggested-by: Sean Christopherson Signed-off-by: Uros Bizjak Cc: Sean Christopherson Cc: Paolo Bonzini Cc: Josh Poimboeuf Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" --- arch/x86/kvm/vmx/vmenter.S | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S index 0a6cf5bff2aa..fb250ddae00b 100644 --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -118,13 +118,23 @@ SYM_FUNC_START(__vmx_vcpu_run) * and vmentry. */ mov 2*WORD_SIZE(%_ASM_SP), %_ASM_DI - movl VMX_spec_ctrl(%_ASM_DI), %edi - movl PER_CPU_VAR(x86_spec_ctrl_current), %esi - cmp %edi, %esi +#ifdef CONFIG_X86_64 + mov VMX_spec_ctrl(%rdi), %rdx + cmp PER_CPU_VAR(x86_spec_ctrl_current), %rdx + je .Lspec_ctrl_done + movl %edx, %eax + shr $32, %rdx +#else + mov VMX_spec_ctrl(%edi), %eax + mov PER_CPU_VAR(x86_spec_ctrl_current), %ecx + xor %eax, %ecx + mov VMX_spec_ctrl + 4(%edi), %edx + mov PER_CPU_VAR(x86_spec_ctrl_current + 4), %edi + xor %edx, %edi + or %edi, %ecx je .Lspec_ctrl_done +#endif mov $MSR_IA32_SPEC_CTRL, %ecx - xor %edx, %edx - mov %edi, %eax wrmsr =20 .Lspec_ctrl_done: --=20 2.50.1