Re: [PATCH v3 5/8] x86/sme: Replace occurrences of sme_active() with cc_platform_has()

Tom Lendacky
2021-09-22T13:40:53Z

On 9/21/21 4:58 PM, Kirill A. Shutemov wrote:
> On Tue, Sep 21, 2021 at 04:43:59PM -0500, Tom Lendacky wrote:
>> On 9/21/21 4:34 PM, Kirill A. Shutemov wrote:
>>> On Tue, Sep 21, 2021 at 11:27:17PM +0200, Borislav Petkov wrote:
>>>> On Wed, Sep 22, 2021 at 12:20:59AM +0300, Kirill A. Shutemov wrote:
>>>>> I still believe calling cc_platform_has() from __startup_64() is totally
>>>>> broken as it lacks proper wrapping while accessing global variables.
>>>>
>>>> Well, one of the issues on the AMD side was using boot_cpu_data too
>>>> early and the Intel side uses it too. Can you replace those checks with
>>>> is_tdx_guest() or whatever was the helper's name which would check
>>>> whether the the kernel is running as a TDX guest, and see if that helps?
>>>
>>> There's no need in Intel check this early. Only AMD need it. Maybe just
>>> opencode them?
>>
>> Any way you can put a gzipped/bzipped copy of your vmlinux file somewhere I
>> can grab it from and take a look at it?
>
> You can find broken vmlinux and bzImage here:
>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fdrive%2Ffolders%2F1n74vUQHOGebnF70Im32qLFY8iS3wvjIs%3Fusp%3Dsharing&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7C1c7adf380cbe4c1a6bb708d97d4af6ff%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637678583935705530%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=gA30x%2Bfu97tUx0p2UqI8HgjiL8bxDbK1GqgJBbUrUE4%3D&amp;reserved=0
>
> Let me know when I can remove it.

Looking at everything, it is all RIP relative addressing, so those
accesses should be fine. Your image has the intel_cc_platform_has()
function, does it work if you remove that call? Because I think it may be
the early call into that function which looks like it has instrumentation
that uses %gs in __sanitizer_cov_trace_pc and %gs is not setup properly
yet. And since boot_cpu_data.x86_vendor will likely be zero this early it
will match X86_VENDOR_INTEL and call into that function.

ffffffff8124f880 <intel_cc_platform_has>:
ffffffff8124f880: e8 bb 64 06 00 callq ffffffff812b5d40 <__fentry__>
ffffffff8124f885: e8 36 ca 42 00 callq ffffffff8167c2c0 <__sanitizer_cov_trace_pc>
ffffffff8124f88a: 31 c0 xor %eax,%eax
ffffffff8124f88c: c3 retq

ffffffff8167c2c0 <__sanitizer_cov_trace_pc>:
ffffffff8167c2c0: 65 8b 05 39 ad 9a 7e mov %gs:0x7e9aad39(%rip),%eax # 27000 <__preempt_count>
ffffffff8167c2c7: 89 c6 mov %eax,%esi
ffffffff8167c2c9: 48 8b 0c 24 mov (%rsp),%rcx
ffffffff8167c2cd: 81 e6 00 01 00 00 and $0x100,%esi
ffffffff8167c2d3: 65 48 8b 14 25 40 70 mov %gs:0x27040,%rdx

Thanks,
Tom