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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.441, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 9/25/25 12:30, YiFei Zhu wrote: > A malicious kernel may control the instruction pointer in SMM in a > multi-processor VM by sending a sequence of IPIs via APIC: > > CPU0 CPU1 > IPI(CPU1, MODE_INIT) > x86_cpu_exec_reset() > apic_init_reset() > s->wait_for_sipi = true > IPI(CPU1, MODE_SMI) > do_smm_enter() > env->hflags |= HF_SMM_MASK; > IPI(CPU1, MODE_STARTUP, vector) > do_cpu_sipi() > apic_sipi() > /* s->wait_for_sipi check passes */ > cpu_x86_load_seg_cache_sipi(vector) > > A different sequence, SMI INIT SIPI, is also buggy in TCG because > INIT is not blocked or latched during SMM. However, it is not > vulnerable to an instruction pointer control in the same way because > x86_cpu_exec_reset clears env->hflags, exiting SMM. Thanks for the reports! For this bug, I prefer to have the CPU eat the SIPI instead of latching them: diff --git a/hw/intc/apic.c b/hw/intc/apic.c index 6d7859640c2..c7680338563 100644 --- a/hw/intc/apic.c +++ b/hw/intc/apic.c @@ -646,8 +646,6 @@ void apic_sipi(DeviceState *dev) { APICCommonState *s = APIC(dev); - cpu_reset_interrupt(CPU(s->cpu), CPU_INTERRUPT_SIPI); - if (!s->wait_for_sipi) return; cpu_x86_load_seg_cache_sipi(s->cpu, s->sipi_vector); diff --git a/target/i386/helper.c b/target/i386/helper.c index 651041ccfa6..a96834c4457 100644 --- a/target/i386/helper.c +++ b/target/i386/helper.c @@ -621,6 +621,9 @@ void do_cpu_init(X86CPU *cpu) void do_cpu_sipi(X86CPU *cpu) { + if (env->hflags & HF_SMM_MASK) { + return; + } apic_sipi(cpu->apic_state); } diff --git a/target/i386/tcg/system/seg_helper.c b/target/i386/tcg/system/seg_helper.c index 38072e51d72..8c7856be81e 100644 --- a/target/i386/tcg/system/seg_helper.c +++ b/target/i386/tcg/system/seg_helper.c @@ -182,6 +182,7 @@ bool x86_cpu_exec_interrupt( apic_poll_irq(cpu->apic_state); break; case CPU_INTERRUPT_SIPI: + cpu_reset_interrupt(cs, CPU_INTERRUPT_SIPI); do_cpu_sipi(cpu); break; case CPU_INTERRUPT_SMI: Fixing INIT is harder, because it requires splitting CPU_INTERRUPT_INIT and CPU_INTERRUPT_RESET, but I'll take a look. Paolo > Fixes: a9bad65d2c1f ("target-i386: wake up processors that receive an SMI") > Signed-off-by: YiFei Zhu > --- > target/i386/cpu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 6d85149e6e..697cc4e63b 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -9762,7 +9762,8 @@ int x86_cpu_pending_interrupt(CPUState *cs, int interrupt_request) > if (interrupt_request & CPU_INTERRUPT_POLL) { > return CPU_INTERRUPT_POLL; > } > - if (interrupt_request & CPU_INTERRUPT_SIPI) { > + if ((interrupt_request & CPU_INTERRUPT_SIPI) && > + !(env->hflags & HF_SMM_MASK)) { > return CPU_INTERRUPT_SIPI; > } >