Re: [PATCH v2 3/4] OvmfPkg/Sec/X64: seed the temporary RAM with PcdInitValueInTempStack

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 15 November 2017 at 21:57, Laszlo Ersek <lersek@redhat.com> wrote:
> This allows the PEI core to report the maximum temporary SEC/PEI stack
> usage on the DEBUG_INFO level, in the PeiCheckAndSwitchStack() function
> [MdeModulePkg/Core/Pei/Dispatcher/Dispatcher.c]:
>
> * Normal boot:
>
>> Temp Stack : BaseAddress=0x814000 Length=0x4000
>> Temp Heap  : BaseAddress=0x810000 Length=0x4000
>> Total temporary memory:    32768 bytes.
>>   temporary memory stack ever used:       5080 bytes. <----
>>   temporary memory heap used for HobList: 8080 bytes.
>>   temporary memory heap occupied by memory pages: 0 bytes.
>
> * S3 resume (no SMM / PEI decompression)
>
>> Temp Stack : BaseAddress=0x814000 Length=0x4000
>> Temp Heap  : BaseAddress=0x810000 Length=0x4000
>> Total temporary memory:    32768 bytes.
>>   temporary memory stack ever used:       5048 bytes. <----
>>   temporary memory heap used for HobList: 7112 bytes.
>>   temporary memory heap occupied by memory pages: 0 bytes.
>
> I unit-tested this change by transitorily adding an infinite loop right
> after the "rep stosq", and dumping the guest's temp SEC/PEI RAM (32KB
> currently) while the guest was stuck in the loop. The dump includes one
> dword from before and after the temp SEC/PEI RAM:
>
>> $ virsh qemu-monitor-command GUEST_NAME --hmp 'xp /8194wx 0x80FFFC'
>>
>> 000000000080fffc: 0x00000000 0x5aa55aa5 0x5aa55aa5 0x5aa55aa5
>> 000000000081000c: 0x5aa55aa5 0x5aa55aa5 0x5aa55aa5 0x5aa55aa5
>> ...
>> 0000000000817fec: 0x5aa55aa5 0x5aa55aa5 0x5aa55aa5 0x5aa55aa5
>> 0000000000817ffc: 0x5aa55aa5 0x00000000
>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=747
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

> ---
>
> Notes:
>     v2:
>     - update comment on ES [Jordan]
>     - document the other segment registers too [Jordan]
>     - move seeding to top of routine, for consistency with the IA32 version
>     - replace runtime right shift with compile-time division [Jordan]
>     - compose qword-to-write at compile-time, not at runtime
>     - drop Ard's Reviewed-by
>
>  OvmfPkg/Sec/X64/SecEntry.nasm | 21 ++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/OvmfPkg/Sec/X64/SecEntry.nasm b/OvmfPkg/Sec/X64/SecEntry.nasm
> index f40427aa8e04..7c55032ac962 100644
> --- a/OvmfPkg/Sec/X64/SecEntry.nasm
> +++ b/OvmfPkg/Sec/X64/SecEntry.nasm
> @@ -30,12 +30,33 @@ extern ASM_PFX(SecCoreStartupWithStack)
>  ; @param[in]  RAX   Initial value of the EAX register (BIST: Built-in Self Test)
>  ; @param[in]  DI    'BP': boot-strap processor, or 'AP': application processor
>  ; @param[in]  RBP   Pointer to the start of the Boot Firmware Volume
> +; @param[in]  DS    Selector allowing flat access to all addresses
> +; @param[in]  ES    Selector allowing flat access to all addresses
> +; @param[in]  FS    Selector allowing flat access to all addresses
> +; @param[in]  GS    Selector allowing flat access to all addresses
> +; @param[in]  SS    Selector allowing flat access to all addresses
>  ;
>  ; @return     None  This routine does not return
>  ;
>  global ASM_PFX(_ModuleEntryPoint)
>  ASM_PFX(_ModuleEntryPoint):
>
> +    ;
> +    ; Fill the temporary RAM with the initial stack value.
> +    ; The loop below will seed the heap as well, but that's harmless.
> +    ;
> +    mov     rax, (FixedPcdGet32 (                        \
> +                    PcdInitValueInTempStack              \
> +                    ) << 32) |                           \
> +                 FixedPcdGet32 (PcdInitValueInTempStack)      ; qword to store
> +    mov     rdi, FixedPcdGet32 (PcdOvmfSecPeiTempRamBase)     ; base address,
> +                                                              ;   relative to
> +                                                              ;   ES
> +    mov     rcx, FixedPcdGet32 (PcdOvmfSecPeiTempRamSize) / 8 ; qword count
> +    cld                                                       ; store from base
> +                                                              ;   up
> +    rep stosq
> +
>      ;
>      ; Load temporary RAM stack based on PCDs
>      ;
> --
> 2.14.1.3.gb7cf6e02401b
>
>