On 01/30/18 21:31, Kinney, Michael D wrote:
> Laszlo,
>
> We have already used this technique in other NASM files
> to remove DBs.
OK.
> Let us know if you have suggestions on how to make the
> C code that performs the patches easier to read and
> maintain.
How about this:
VOID
PatchAssembly (
VOID *BufferEnd,
UINT64 PatchValue,
UINTN ValueSize
)
{
CopyMem (
(VOID *)((UINTN)BufferEnd - ValueSize),
&PatchValue,
ValueSize
);
}
extern UINT8 gAsmSmmCr0;
extern UINT8 gAsmSmmCr3;
extern UINT8 gAsmSmmCr4;
...
{
PatchAssembly (&gAsmSmmCr0, AsmReadCr0 (), 4);
PatchAssembly (&gAsmSmmCr3, AsmReadCr3 (), 4);
PatchAssembly (&gAsmSmmCr4, AsmReadCr4 (), 4);
...
}
(I think it's fine to open-code the last argument as "4", rather than
"sizeof (UINT32)", because for patching, we must have intimate knowledge
of the instruction anyway.)
To me, this is easier to read, because:
- there are no complex casts in the "business logic"
- the size is spelled out once per patching
- the function name and the variable names make it clear we are patching
separately compiled assembly code that was linked into the same
module.
What do you think?
Thanks!
Laszlo
>> -----Original Message-----
>> From: edk2-devel [mailto:[email protected]]
>> On Behalf Of Laszlo Ersek
>> Sent: Tuesday, January 30, 2018 10:17 AM
>> To: Kinney, Michael D <[email protected]>; edk2-
>> devel-01 <[email protected]>
>> Cc: Ni, Ruiyu <[email protected]>; Paolo Bonzini
>> <[email protected]>; Yao, Jiewen
>> <[email protected]>; Dong, Eric <[email protected]>
>> Subject: Re: [edk2] [PATCH 1/3]
>> UefiCpuPkg/PiSmmCpuDxeSmm: update comments in IA32
>> SmmStartup()
>>
>> On 01/30/18 18:22, Kinney, Michael D wrote:
>>> Laszlo,
>>>
>>> The DBs can be removed if the label is moved after
>>> the instruction and the patch is done to the label
>>> minus the size of the patch value.
>>
>> Indeed I haven't thought of this.
>>
>> If I understand correctly, it means
>>
>> extern UINT8 gSmmCr0;
>>
>> *(UINT32*)(&gSmmCr0 - sizeof (UINT32)) =
>> (UINT32)AsmReadCr0 ();
>>
>> TBH, the DB feels less ugly to me than this :)
>>
>> Still, if you think it would be an acceptable price to
>> pay for removing
>> the remaining DBs, I can respin.
>>
>> Thanks
>> Laszlo
>>
>>>> -----Original Message-----
>>>> From: edk2-devel [mailto:edk2-devel-
>> [email protected]]
>>>> On Behalf Of Laszlo Ersek
>>>> Sent: Tuesday, January 30, 2018 7:34 AM
>>>> To: edk2-devel-01 <[email protected]>
>>>> Cc: Ni, Ruiyu <[email protected]>; Yao, Jiewen
>>>> <[email protected]>; Dong, Eric
>> <[email protected]>;
>>>> Paolo Bonzini <[email protected]>
>>>> Subject: [edk2] [PATCH 1/3] UefiCpuPkg/PiSmmCpuDxeSmm:
>>>> update comments in IA32 SmmStartup()
>>>>
>>>> The gSmmCr3, gSmmCr4, gSmmCr0 and gSmmJmpAddr global
>>>> variables are used
>>>> for patching assembly instructions, thus we can never
>>>> remove the DB
>>>> encodings for those instructions. At least we should
>> add
>>>> the intended
>>>> meanings in comments.
>>>>
>>>> This patch only changes comments.
>>>>
>>>> Cc: Eric Dong <[email protected]>
>>>> Cc: Jian J Wang <[email protected]>
>>>> Cc: Jiewen Yao <[email protected]>
>>>> Cc: Paolo Bonzini <[email protected]>
>>>> Cc: Ruiyu Ni <[email protected]>
>>>> Contributed-under: TianoCore Contribution Agreement
>> 1.1
>>>> Signed-off-by: Laszlo Ersek <[email protected]>
>>>> ---
>>>> UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm | 8 ++++-
>> ---
>>>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git
>> a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
>>>> b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
>>>> index e96dd8d2392a..08534dba64b7 100644
>>>> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
>>>> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
>>>> @@ -44,34 +44,34 @@ global ASM_PFX(SmmStartup)
>>>> ASM_PFX(SmmStartup):
>>>> DB 0x66
>>>> mov eax, 0x80000001 ; read
>>>> capability
>>>> cpuid
>>>> DB 0x66
>>>> mov ebx, edx ; rdmsr will
>>>> change edx. keep it in ebx.
>>>> - DB 0x66, 0xb8
>>>> + DB 0x66, 0xb8 ; mov eax,
>> imm32
>>>> ASM_PFX(gSmmCr3): DD 0
>>>> mov cr3, eax
>>>> DB 0x67, 0x66
>>>> lgdt [cs:ebp + (ASM_PFX(gcSmiInitGdtr) -
>>>> ASM_PFX(SmmStartup))]
>>>> - DB 0x66, 0xb8
>>>> + DB 0x66, 0xb8 ; mov eax,
>> imm32
>>>> ASM_PFX(gSmmCr4): DD 0
>>>> mov cr4, eax
>>>> DB 0x66
>>>> mov ecx, 0xc0000080 ; IA32_EFER
>> MSR
>>>> rdmsr
>>>> DB 0x66
>>>> test ebx, BIT20 ; check NXE
>>>> capability
>>>> jz .1
>>>> or ah, BIT3 ; set NXE bit
>>>> wrmsr
>>>> .1:
>>>> - DB 0x66, 0xb8
>>>> + DB 0x66, 0xb8 ; mov eax,
>> imm32
>>>> ASM_PFX(gSmmCr0): DD 0
>>>> DB 0xbf, PROTECT_MODE_DS, 0 ; mov di,
>>>> PROTECT_MODE_DS
>>>> mov cr0, eax
>>>> - DB 0x66, 0xea ; jmp far
>>>> [ptr48]
>>>> + DB 0x66, 0xea ; jmp far
>>>> [ptr48]
>>>> ASM_PFX(gSmmJmpAddr):
>>>> DD @32bit
>>>> DW PROTECT_MODE_CS
>>>> @32bit:
>>>> mov ds, edi
>>>> mov es, edi
>>>> --
>>>> 2.14.1.3.gb7cf6e02401b
>>>>
>>>>
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>>
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