Re: [PATCH] x86/microcode/intel: Ensure new microcode processor flags match with cpu's pf

Zhenzhong Duan
2018-06-19T04:50:07Z

On 2018/6/19 3:56, Borislav Petkov wrote:
> On Mon, Jun 04, 2018 at 08:16:51AM +0000, Zhenzhong Duan wrote:
>> Intel spec says: 'The processor flags in the 48-byte header and the
>> processor flags field associated with the extended processor signature
>> structures may have multiple bits set.'
>>
>> Make sure processor flags of the new microcode intersect with current
>> cpu's. Comparing with old microcode's pf can't guarantee this.
>>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>> ---
>> arch/x86/kernel/cpu/microcode/intel.c | 8 +++-----
>> 1 files changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
>> index 461e315..54f4014 100644
>> --- a/arch/x86/kernel/cpu/microcode/intel.c
>> +++ b/arch/x86/kernel/cpu/microcode/intel.c
>> @@ -371,12 +371,10 @@ static int microcode_sanity_check(void *mc, int print_err)
>> goto next;
>>
>> } else {
>> - struct microcode_header_intel *phdr = &patch->hdr;
>> -
>> if (!has_newer_microcode(data,
>> - phdr->sig,
>> - phdr->pf,
>> - phdr->rev))
>> + uci->cpu_sig.sig,
>> + uci->cpu_sig.pf,
>> + patch->hdr.rev))
>> goto next;
>> }
>>
>> --
>
> So I'm scratching my head over this and have no clue what you're trying
> to achieve. Is this a fix for a bug you're seeing or what? You'd need to
> be a lot more verbose when explaining what this patch is trying to do...
Imagine kernel already found a microcode blob A with extended sig/pf
matching current cpu, then another microcode B is checked which doesn't
match current cpu but matches the sig/pf of microcode A, then microcode
B will replaced A, but it's not suitable for current cpu.

I didn't see same issue in our system. When fixing another bug and
reading upstream microcode code, I found this potential issue, feel free
to correct me if it's never possible in reality.

Thanks
Zhenzhong