Re: [PATCH] UefiCpuPkg/CpuMpPei: fix unsafe way to get stack pointer

[Jordan Justen <jordan.l.justen@intel.com>]

I guess the git config sendemail.from setting did not help your
patches. ?? It still is coming through with a From field of
<edk2-devel-bounces@lists.01.org>.

Regarding this patch, I suppose it is worth asking if &StackBase in
the old code could possibly be an address not on the stack. I don't
think it is possible, and I'm guessing the C specification would
probably back that up.

It can be unsafe to get an address of something on the stack and then
refer to that address after the variable is no longer in scope. I
suspect this is what the static checker is noticing. By calling
SetJump, aren't we just doing the same thing, but hiding what we are
doing from the static checker?

So, can't we just tell the static checker to ignore the error because
we know what we are doing?

-Jordan

On 2018-09-18 02:04:48,  wrote:
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1186
> 
> This patch uses SetJump() to get the stack pointer from esp/rsp
> register to replace local variable way, which was marked by static
> code checker as an unsafe way.
> 
> Cc: Dandan Bi <dandan.bi@intel.com>
> Cc: Hao A Wu <hao.a.wu@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>  UefiCpuPkg/CpuMpPei/CpuMpPei.h  | 8 ++++++++
>  UefiCpuPkg/CpuMpPei/CpuPaging.c | 9 +++++++--
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.h b/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> index d097a66aa8..fe61f5e3bc 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> +++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.h
> @@ -35,6 +35,14 @@
>  
>  extern EFI_PEI_PPI_DESCRIPTOR   mPeiCpuMpPpiDesc;
>  
> +#if   defined (MDE_CPU_IA32)
> +#define CPU_STACK_POINTER(Context)  ((Context).Esp)
> +#elif defined (MDE_CPU_X64)
> +#define CPU_STACK_POINTER(Context)  ((Context).Rsp)
> +#else
> +#error CPU type not supported!
> +#endif
> +
>  /**
>    This service retrieves the number of logical processor in the platform
>    and the number of those logical processors that are enabled on this boot.
> diff --git a/UefiCpuPkg/CpuMpPei/CpuPaging.c b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> index c7e0822452..997c20c26e 100644
> --- a/UefiCpuPkg/CpuMpPei/CpuPaging.c
> +++ b/UefiCpuPkg/CpuMpPei/CpuPaging.c
> @@ -517,9 +517,14 @@ GetStackBase (
>    IN OUT VOID *Buffer
>    )
>  {
> -  EFI_PHYSICAL_ADDRESS    StackBase;
> +  EFI_PHYSICAL_ADDRESS      StackBase;
> +  BASE_LIBRARY_JUMP_BUFFER  Context;
>  
> -  StackBase = (EFI_PHYSICAL_ADDRESS)(UINTN)&StackBase;
> +  //
> +  // Retrieve stack pointer from current processor context.
> +  //
> +  SetJump (&Context);
> +  StackBase = (EFI_PHYSICAL_ADDRESS)CPU_STACK_POINTER (Context);
>    StackBase += BASE_4KB;
>    StackBase &= ~((EFI_PHYSICAL_ADDRESS)BASE_4KB - 1);
>    StackBase -= PcdGet32(PcdCpuApStackSize);
> -- 
> 2.16.2.windows.1
> 
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