Re: [RFC v2 1/3] UefiCpuPkg/CpuExceptionHandlerLib/X64: Add stack trace support

["Brian J. Johnson" <brian.johnson@hpe.com>]

On 11/15/2017 07:18 PM, Paulo Alcantara wrote:
> This patch adds stack trace support during a X64 CPU exception.
> 
> It will dump out back trace, stack contents as well as image module
> names that were part of the call stack.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Paulo Alcantara <pcacjr@zytor.com>

(These comments apply to patch 3/3 as well.)

Typo:  UnwondStacksCount should be UnwoundStacksCount

It's good to check the alignment of the stack, as you're doing.  But 
I'll reiterate that you absolutely need some better sanity checking of 
the stack and IP addresses before you dereference them.  Remember that 
they could be absolutely *anything* at the entry to this code. 
Something caused an error, and it may have been one of those registers.

Also, if the code was built with a compiler which isn't using RBP as a 
base pointer, RBP is unlikely to contain a stack address.  That will 
cause issues if you use it for unwinding without a sanity check.

Thanks,
Brian

> ---
>   UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c | 369 +++++++++++++++++++-
>   1 file changed, 367 insertions(+), 2 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> index 65f0cff680..11cd7c9e1c 100644
> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> @@ -14,6 +14,11 @@
>   
>   #include "CpuExceptionCommon.h"
>   
> +//
> +// Unknown PDB file name
> +//
> +GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 *mUnknownPdbFileName = "????";
> +
>   /**
>     Return address map of exception handler template so that C code can generate
>     exception tables.
> @@ -242,6 +247,350 @@ DumpCpuContext (
>       );
>   }
>   
> +/**
> +  Get absolute path and file name of PDB file in PE/COFF image.
> +
> +  @param[in]  ImageBase            Base address of PE/COFF image.
> +  @param[out] PdbAbsoluteFilePath  Absolute path of PDB file.
> +  @param[out] PdbFileName          File name of PDB file.
> +**/
> +STATIC
> +VOID
> +GetPdbFileName (
> +  IN  UINTN    ImageBase,
> +  OUT CHAR8    **PdbAbsoluteFilePath,
> +  OUT CHAR8    **PdbFileName
> +  )
> +{
> +  VOID   *PdbPointer;
> +  CHAR8  *Str;
> +
> +  //
> +  // Get PDB file name from PE/COFF image
> +  //
> +  PdbPointer = PeCoffLoaderGetPdbPointer ((VOID *)ImageBase);
> +  if (PdbPointer == NULL) {
> +    //
> +    // No PDB file name found. Set it to an unknown file name.
> +    //
> +    *PdbFileName = (CHAR8 *)mUnknownPdbFileName;
> +    if (PdbAbsoluteFilePath != NULL) {
> +      *PdbAbsoluteFilePath = NULL;
> +    }
> +  } else {
> +    //
> +    // Get file name portion out of PDB file in PE/COFF image
> +    //
> +    Str = (CHAR8 *)((UINTN)PdbPointer +
> +                    AsciiStrLen ((CHAR8 *)PdbPointer) - sizeof *Str);
> +    for (; *Str != '/' && *Str != '\\'; Str--) {
> +      ;
> +    }
> +
> +    //
> +    // Set PDB file name (also skip trailing path separator: '/' or '\\')
> +    //
> +    *PdbFileName = Str + 1;
> +
> +    if (PdbAbsoluteFilePath != NULL) {
> +      //
> +      // Set absolute file path of PDB file
> +      //
> +      *PdbAbsoluteFilePath = PdbPointer;
> +    }
> +  }
> +}
> +
> +/**
> +  Dump stack contents.
> +
> +  @param[in]  CurrentRsp         Current stack pointer address.
> +  @param[in]  UnwondStacksCount  Count of unwond stack frames.
> +**/
> +STATIC
> +VOID
> +DumpStackContents (
> +  IN UINT64  CurrentRsp,
> +  IN INTN    UnwondStacksCount
> +  )
> +{
> +  //
> +  // Check for proper stack pointer alignment
> +  //
> +  if (((UINTN)CurrentRsp & (CPU_STACK_ALIGNMENT - 1)) != 0) {
> +    InternalPrintMessage ("!!!! Unaligned stack pointer. !!!!\n");
> +    return;
> +  }
> +
> +  //
> +  // Dump out stack contents
> +  //
> +  InternalPrintMessage ("\nStack dump:\n");
> +  while (UnwondStacksCount-- > 0) {
> +    InternalPrintMessage (
> +      "0x%016lx: %016lx %016lx\n",
> +      CurrentRsp,
> +      *(UINT64 *)CurrentRsp,
> +      *(UINT64 *)((UINTN)CurrentRsp + 8)
> +      );
> +
> +    //
> +    // Point to next stack
> +    //
> +    CurrentRsp += CPU_STACK_ALIGNMENT;
> +  }
> +}
> +
> +/**
> +  Dump all image module names from call stack.
> +
> +  @param[in]  SystemContext  Pointer to EFI_SYSTEM_CONTEXT.
> +**/
> +STATIC
> +VOID
> +DumpImageModuleNames (
> +  IN EFI_SYSTEM_CONTEXT   SystemContext
> +  )
> +{
> +  EFI_STATUS  Status;
> +  UINT64      Rip;
> +  UINTN       ImageBase;
> +  VOID        *EntryPoint;
> +  CHAR8       *PdbAbsoluteFilePath;
> +  CHAR8       *PdbFileName;
> +  UINT64      Rbp;
> +
> +  //
> +  // Set current RIP address
> +  //
> +  Rip = SystemContext.SystemContextX64->Rip;
> +
> +  //
> +  // Set current frame pointer address
> +  //
> +  Rbp = SystemContext.SystemContextX64->Rbp;
> +
> +  //
> +  // Check for proper frame pointer alignment
> +  //
> +  if (((UINTN)Rbp & (CPU_STACK_ALIGNMENT - 1)) != 0) {
> +    InternalPrintMessage ("!!!! Unaligned frame pointer. !!!!\n");
> +    return;
> +  }
> +
> +  //
> +  // Get initial PE/COFF image base address from current RIP
> +  //
> +  ImageBase = PeCoffSearchImageBase (Rip);
> +  if (ImageBase == 0) {
> +    InternalPrintMessage ("!!!! Could not find image module names. !!!!");
> +    return;
> +  }
> +
> +  //
> +  // Get initial PE/COFF image's entry point
> +  //
> +  Status = PeCoffLoaderGetEntryPoint ((VOID *)ImageBase, &EntryPoint);
> +  if (EFI_ERROR (Status)) {
> +    EntryPoint = NULL;
> +  }
> +
> +  //
> +  // Get file name and absolute path of initial PDB file
> +  //
> +  GetPdbFileName (ImageBase, &PdbAbsoluteFilePath, &PdbFileName);
> +
> +  //
> +  // Print out initial image module name (if any)
> +  //
> +  if (PdbAbsoluteFilePath != NULL) {
> +    InternalPrintMessage (
> +      "\n%a (ImageBase=0x%016lx, EntryPoint=0x%016lx):\n",
> +      PdbFileName,
> +      ImageBase,
> +      (UINTN)EntryPoint
> +      );
> +    InternalPrintMessage ("%a\n", PdbAbsoluteFilePath);
> +  }
> +
> +  //
> +  // Walk through call stack and find next module names
> +  //
> +  for (;;) {
> +    //
> +    // Set RIP with return address from current stack frame
> +    //
> +    Rip = *(UINT64 *)((UINTN)Rbp + 8);
> +
> +    //
> +    // If RIP is zero, then stop unwinding the stack
> +    //
> +    if (Rip == 0) {
> +      break;
> +    }
> +
> +    //
> +    // Check if RIP is within another PE/COFF image base address
> +    //
> +    if (Rip < ImageBase) {
> +      //
> +      // Search for the respective PE/COFF image based on RIP
> +      //
> +      ImageBase = PeCoffSearchImageBase (Rip);
> +      if (ImageBase == 0) {
> +        //
> +        // Stop stack trace
> +        //
> +        break;
> +      }
> +
> +      //
> +      // Get PE/COFF image's entry point
> +      //
> +      Status = PeCoffLoaderGetEntryPoint ((VOID *)ImageBase, &EntryPoint);
> +      if (EFI_ERROR (Status)) {
> +        EntryPoint = NULL;
> +      }
> +
> +      //
> +      // Get file name and absolute path of PDB file
> +      //
> +      GetPdbFileName (ImageBase, &PdbAbsoluteFilePath, &PdbFileName);
> +
> +      //
> +      // Print out image module name (if any)
> +      //
> +      if (PdbAbsoluteFilePath != NULL) {
> +        InternalPrintMessage (
> +          "%a (ImageBase=0x%016lx, EntryPoint=0x%016lx):\n",
> +          PdbFileName,
> +          ImageBase,
> +          (UINTN)EntryPoint
> +          );
> +        InternalPrintMessage ("%a\n", PdbAbsoluteFilePath);
> +      }
> +    }
> +
> +    //
> +    // Unwind the stack
> +    //
> +    Rbp = *(UINT64 *)(UINTN)Rbp;
> +  }
> +}
> +
> +/**
> +  Dump stack trace.
> +
> +  @param[in]  SystemContext      Pointer to EFI_SYSTEM_CONTEXT.
> +  @param[out] UnwondStacksCount  Count of unwond stack frames.
> +**/
> +STATIC
> +VOID
> +DumpStackTrace (
> +  IN  EFI_SYSTEM_CONTEXT   SystemContext,
> +  OUT INTN                 *UnwondStacksCount
> +  )
> +{
> +  UINT64  Rip;
> +  UINT64  Rbp;
> +  UINTN   ImageBase;
> +  CHAR8   *PdbFileName;
> +
> +  //
> +  // Set current RIP address
> +  //
> +  Rip = SystemContext.SystemContextX64->Rip;
> +
> +  //
> +  // Set current frame pointer address
> +  //
> +  Rbp = SystemContext.SystemContextX64->Rbp;
> +
> +  //
> +  // Get initial PE/COFF image base address from current RIP
> +  //
> +  ImageBase = PeCoffSearchImageBase (Rip);
> +  if (ImageBase == 0) {
> +    InternalPrintMessage ("!!!! Could not find backtrace information. !!!!");
> +    return;
> +  }
> +
> +  //
> +  // Get PDB file name from initial PE/COFF image
> +  //
> +  GetPdbFileName (ImageBase, NULL, &PdbFileName);
> +
> +  //
> +  // Initialize count of unwond stacks
> +  //
> +  *UnwondStacksCount = 1;
> +
> +  //
> +  // Print out back trace
> +  //
> +  InternalPrintMessage ("\nCall trace:\n");
> +
> +  for (;;) {
> +    //
> +    // Print stack frame in the following format:
> +    //
> +    // # <RIP> @ <ImageBase>+<RelOffset> (RBP) in [<ModuleName> | ????]
> +    //
> +    InternalPrintMessage (
> +      "%d 0x%016lx @ 0x%016lx+0x%x (0x%016lx) in %a\n",
> +      *UnwondStacksCount - 1,
> +      Rip,
> +      ImageBase,
> +      Rip - ImageBase - 1,
> +      Rbp,
> +      PdbFileName
> +      );
> +
> +    //
> +    // Set RIP with return address from current stack frame
> +    //
> +    Rip = *(UINT64 *)((UINTN)Rbp + 8);
> +
> +    //
> +    // If RIP is zero, then stop unwinding the stack
> +    //
> +    if (Rip == 0) {
> +      break;
> +    }
> +
> +    //
> +    // Check if RIP is within another PE/COFF image base address
> +    //
> +    if (Rip < ImageBase) {
> +      //
> +      // Search for the respective PE/COFF image based on RIP
> +      //
> +      ImageBase = PeCoffSearchImageBase (Rip);
> +      if (ImageBase == 0) {
> +        //
> +        // Stop stack trace
> +        //
> +        break;
> +      }
> +
> +      //
> +      // Get PDB file name
> +      //
> +      GetPdbFileName (ImageBase, NULL, &PdbFileName);
> +    }
> +
> +    //
> +    // Unwind the stack
> +    //
> +    Rbp = *(UINT64 *)(UINTN)Rbp;
> +
> +    //
> +    // Increment count of unwond stacks
> +    //
> +    (*UnwondStacksCount)++;
> +  }
> +}
> +
>   /**
>     Display CPU information.
>   
> @@ -254,9 +603,25 @@ DumpImageAndCpuContent (
>     IN EFI_SYSTEM_CONTEXT   SystemContext
>     )
>   {
> +  INTN UnwondStacksCount;
> +
> +  //
> +  // Dump CPU context
> +  //
>     DumpCpuContext (ExceptionType, SystemContext);
> +
> +  //
> +  // Dump stack trace
> +  //
> +  DumpStackTrace (SystemContext, &UnwondStacksCount);
> +
> +  //
> +  // Dump image module names
> +  //
> +  DumpImageModuleNames (SystemContext);
> +
>     //
> -  // Dump module image base and module entry point by RIP
> +  // Dump stack contents
>     //
> -  DumpModuleImageInfo (SystemContext.SystemContextX64->Rip);
> +  DumpStackContents (SystemContext.SystemContextX64->Rsp, UnwondStacksCount);
>   }
> 


-- 
Brian J. Johnson
Enterprise X86 Lab

Hewlett Packard Enterprise

brian.johnson@hpe.com