[U-Boot] [PATCH 2/3] efi_loader: add checking for incorrect use of EFI_ENTRY/EXIT

[Alexander Graf]

On 26.07.17 15:55, Rob Clark wrote:
> Missing an EFI_ENTRY() or doubling up EFI_EXIT() leads to non-obvious
> crashes.  Let's add some error checking.
> 
> Signed-off-by: Rob Clark <robdclark at gmail.com>
> ---
>   include/efi_loader.h          |  5 +++++
>   lib/efi_loader/efi_boottime.c | 13 +++++++++++++
>   2 files changed, 18 insertions(+)
> 
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 09bab7dbc6..4b49fac84b 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -15,11 +15,13 @@
>   
>   #include <linux/list.h>
>   
> +int __efi_check_nesting(int delta);
>   /*
>    * Enter the u-boot world from UEFI:
>    */
>   #define EFI_ENTRY(format, ...) do { \
>   	efi_restore_gd(); \
> +	assert(__efi_check_nesting(+1)); \
>   	debug("EFI: Entry %s(" format ")\n", __func__, ##__VA_ARGS__); \
>   	} while(0)
>   
> @@ -28,6 +30,7 @@
>    */
>   #define EFI_EXIT(ret) ({ \
>   	debug("EFI: Exit: %s: %u\n", __func__, (u32)((ret) & ~EFI_ERROR_MASK)); \
> +	assert(__efi_check_nesting(-1)); \
>   	efi_exit_func(ret); \
>   	})
>   
> @@ -36,10 +39,12 @@
>    */
>   #define EFI_CALL(exp) do { \
>   	debug("EFI: Call: %s\n", #exp); \
> +	assert(__efi_check_nesting(-1)); \
>   	efi_exit_func(EFI_SUCCESS); \
>   	exp; \
>   	efi_restore_gd(); \
>   	debug("EFI: Return From: %s\n", #exp); \
> +	assert(__efi_check_nesting(+1)); \
>   	} while(0)
>   
>   extern struct efi_runtime_services efi_runtime_services;
> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
> index 76cafffc1d..b21df7bd5d 100644
> --- a/lib/efi_loader/efi_boottime.c
> +++ b/lib/efi_loader/efi_boottime.c
> @@ -57,6 +57,17 @@ void efi_save_gd(void)
>   #endif
>   }
>   
> +/* Check for incorrect use of EFI_ENTRY() / EFI_EXIT() */
> +int __efi_check_nesting(int delta)
> +{
> +	static int entry_count;

I'd prefer if we marked globals as such (read: somewhere at the top of a 
.c file).

Also I think this function would be better off as a static inline in a 
header, as it should get compressed quite well.

> +	/* post-increment, pre-decrement: */
> +	if (delta > 0)
> +		return entry_count++ == 0;
> +	else
> +		return --entry_count == 0;

I have a hard time to wrap my head around the logic. At least, couldn't 
you split this into 2 functions? :)

Alex

> +}
> +
>   /* Called on every callback entry */
>   void efi_restore_gd(void)
>   {
> @@ -716,7 +727,9 @@ static efi_status_t EFIAPI efi_start_image(efi_handle_t image_handle,
>   		return EFI_EXIT(info->exit_status);
>   	}
>   
> +	__efi_check_nesting(-1);
>   	entry(image_handle, &systab);
> +	__efi_check_nesting(+1);
>   
>   	/* Should usually never get here */
>   	return EFI_EXIT(EFI_SUCCESS);
>