Re: [PATCH 62/65] x86/entry: Make IDT entrypoints CET-IBT compatible

[Andrew Cooper <amc96@xxxxxxxx>]

On 03/12/2021 13:23, Jan Beulich wrote:
> On 26.11.2021 13:34, Andrew Cooper wrote:
>> Each IDT vector needs to land on an endbr64 instruction.  This is especially
>> important for the #CP handler, which will escalate to #DF if the endbr64 is
>> missing.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks.

>
> One remark though:
>
>> @@ -1136,7 +1158,8 @@ autogen_stubs: /* Automatically generated stubs. */
>>  #endif
>>  
>>          ALIGN
>> -1:      pushq $0
>> +1:      ENDBR64
>> +        pushq $0
>>          movb  $vec,4(%rsp)
>>          jmp   common_interrupt
>>  
>> @@ -1146,7 +1169,8 @@ autogen_stubs: /* Automatically generated stubs. */
>>          .elseif vec == X86_EXC_CSO || vec == X86_EXC_SPV || \
>>                  vec == X86_EXC_VE  || (vec > X86_EXC_CP && vec < TRAP_nr)
>>  
>> -1:      test  $8,%spl        /* 64bit exception frames are 16 byte aligned, 
>> but the word */
>> +1:      ENDBR64
>> +        test  $8,%spl        /* 64bit exception frames are 16 byte aligned, 
>> but the word */
>>          jz    2f             /* size is 8 bytes.  Check whether the 
>> processor gave us an */
>>          pushq $0             /* error code, and insert an empty one if not. 
>>              */
>>  2:      movb  $vec,4(%rsp)
> Like with initializers of compound objects vs trailing commas there, I
> think it would help if we moved away from placing insns on the same
> lines as labels. As can be seen here, inserting something always means
> touching two lines instead of just adding one.

I had actually wondered the same, without drawing a comparison to
trailing commas.  I'll adjust.

~Andrew