Re: [kvm-unit-tests PATCH] x86/emulator: Test POP-SS blocking

Michal Luczaj
2022-08-25T17:32:42Z

On 8/25/22 19:03, Sean Christopherson wrote:
> On Wed, Aug 24, 2022, Michal Luczaj wrote:
>> \
>> n = 0; \
>> asm volatile(/* jump to 32-bit code segment */ \
>> "ljmp *1f\n\t" \
>> "1:\n\t" \
>> " .long 2f\n\t" \
>> " .word " xstr(KERNEL_CS32) "\n\t" \
>> /* exercise POP SS blocking */ \
>> ".code32\n\t" \
>> "2: lea 3f, %0\n\t" \
>> "mov %0, %%dr0\n\t" \
>> "push %%ss\n\t" \
>> fep1 "pop %%ss\n\t" \
>> fep2 "3: xor %0, %0\n\t" \
>> /* back to long mode */ \
>> "ljmp %[cs64], $4f\n\t" \
>> ".code64\n\t" \
>
> Ooh, I see what you meant by temporarily switching to 32-bit mode. I was thinking
> we could just make the POP SS testcase 32-bit only, but I didn't realize this test
> is 64-bit only. Argh, and so is emulate.c. And now I get why you added a brand
> new test.
>
> Let's just add a new test. The above can work, but it relies on the code and
> stack being mapped with a 32-bit address, e.g. will break if KUT is ever changed
> to not map everything low in the virtual address space.

Yeah, it is fragile in that sense. But does it mean code such as
vmx_tests.c:into_guest_main() or svm_tests.c:svm_of_test_guest() should be moved
to 32-bit binaries?

Michal