Re: [PATCH v15 10/23] KVM: selftests: Set up TDX boot parameters region

[Lisa Wang <wyihan@google.com>]

On Fri, Oct 02, 2026 at 09:13:29AM +0000, sashiko-bot@kernel.org wrote:
> [ ... ]
> > +	/* Set parameters! */
> > +	params->cr0 = kvm_get_default_cr0();
> > +	TEST_ASSERT(vm->mmu.pgd < (1ULL << 32),
> > +		    "PGD must be within 32-bit address space for 32-bit boot code");
> > +	params->cr3 = vm->mmu.pgd;
> > +	params->cr4 = cr4;
> > +	params->idtr.base = vm->arch.idt;
> > +	params->idtr.limit = kvm_get_default_idt_limit();
> > +	params->gdtr.base = vm->arch.gdt;
> > +	params->gdtr.limit = kvm_get_default_gdt_limit();
> > +
> > +	TEST_ASSERT(params->idtr.base < (1ULL << 32),
> > +		    "idt must be within 32-bit address space for 32-bit boot code");
> > +	TEST_ASSERT(params->gdtr.base < (1ULL << 32),
> > +		    "gdt must be within 32-bit address space for 32-bit boot code");
> 
> [Severity: Low]
> Does this assignment silently truncate the 64-bit vm->arch.idt and
> vm->arch.gdt addresses?
> 
> Since params->idtr.base and params->gdtr.base are 32-bit fields, the
> subsequent TEST_ASSERT checks evaluate the already-truncated values. If a
> test allocates an IDT or GDT address beyond 4GB, the assertions will
> always be trivially true because the upper 32 bits are lost before the
> check.
> 
> This could lead to confusing test failures during guest execution instead
> of properly failing the assertion here.
> 
> Should these assertions check vm->arch.idt and vm->arch.gdt directly
> before assigning them to the base fields?

Will update the assertions to check vm->arch.idt and vm->arch.gdt directly.