[U-Boot] [PATCH] efi_loader: Patch non-runtime code out at ExitBootServices already

[Heinrich Schuchardt]

On 1/23/19 6:33 PM, Alexander Graf wrote:
> While discussing something compeltely different, Ard pointed out
> that it might be legal to omit calling SetVirtualAddressMap altogether.
> 
> While that sounds great, we currently rely on that call to remove
> all function pointers to code that we do not support outside of
> boot services.
> 
> So let's patch out those bits already on the call to ExitBootServices,
> so that we can successfully run even when an OS chooses to omit
> any call to SetVirtualAddressMap.

Such an operating system would not be allowed to use any virtual
addresses at any time because runtime drivers would not be informed
about the mapping.

Does such an operating system exist?
Or is this only a hypothetical case?

> 
> Reported-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Signed-off-by: Alexander Graf <agraf at suse.de>

I am missing a description of the side effects of the change, e.g.

Our EFI unit tests call the Reset() service.

So Python tests will fail on systems that do not implement Reset() in a
runtime compatible manner.

Best regards

Heinrich


> ---
>  include/efi_loader.h          |  2 ++
>  lib/efi_loader/efi_boottime.c |  1 +
>  lib/efi_loader/efi_runtime.c  | 27 ++++++++++++++++++---------
>  3 files changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 9dd933dae7..2a40b09693 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -310,6 +310,8 @@ void efi_save_gd(void);
>  void efi_restore_gd(void);
>  /* Call this to relocate the runtime section to an address space */
>  void efi_runtime_relocate(ulong offset, struct efi_mem_desc *map);
> +/* Call this when we start to live in a runtime only world */
> +void efi_runtime_detach(ulong offset);
>  /* Call this to set the current device name */
>  void efi_set_bootdev(const char *dev, const char *devnr, const char *path);
>  /* Add a new object to the object list. */
> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
> index fc26d6adc1..8cb2979bab 100644
> --- a/lib/efi_loader/efi_boottime.c
> +++ b/lib/efi_loader/efi_boottime.c
> @@ -1917,6 +1917,7 @@ static efi_status_t EFIAPI efi_exit_boot_services(efi_handle_t image_handle,
>  	bootm_disable_interrupts();
>  
>  	/* Disable boot time services */
> +	efi_runtime_detach((ulong)gd->relocaddr);
>  	systab.con_in_handle = NULL;
>  	systab.con_in = NULL;
>  	systab.con_out_handle = NULL;
> diff --git a/lib/efi_loader/efi_runtime.c b/lib/efi_loader/efi_runtime.c
> index 636dfdab39..ec7fedba06 100644
> --- a/lib/efi_loader/efi_runtime.c
> +++ b/lib/efi_loader/efi_runtime.c
> @@ -276,16 +276,12 @@ struct efi_runtime_detach_list_struct {
>  	void *patchto;
>  };
>  
> -static const struct efi_runtime_detach_list_struct efi_runtime_detach_list[] = {
> +static struct efi_runtime_detach_list_struct efi_runtime_detach_list[] = {
>  	{
>  		/* do_reset is gone */
>  		.ptr = &efi_runtime_services.reset_system,
>  		.patchto = efi_reset_system,
>  	}, {
> -		/* invalidate_*cache_all are gone */
> -		.ptr = &efi_runtime_services.set_virtual_address_map,
> -		.patchto = &efi_unimplemented,
> -	}, {
>  		/* RTC accessors are gone */
>  		.ptr = &efi_runtime_services.get_time,
>  		.patchto = &efi_get_time,
> @@ -328,7 +324,15 @@ static bool efi_runtime_tobedetached(void *p)
>  	return false;
>  }
>  
> -static void efi_runtime_detach(ulong offset)
> +/**
> + * efi_runtime_detach() - Remove any dependency on non-runtime sections
> + *
> + * This function patches all remaining code to be self-sufficient inside
> + * runtime sections. Any calls to non-runtime will be removed after this.
> + *
> + * @offset:		relocaddr for pre-set_v_a_space, offset to VA after
> + */
> +__efi_runtime void efi_runtime_detach(ulong offset)
>  {
>  	int i;
>  	ulong patchoff = offset - (ulong)gd->relocaddr;
> @@ -430,19 +434,25 @@ void efi_runtime_relocate(ulong offset, struct efi_mem_desc *map)
>   * @virtmap:		virtual address mapping information
>   * Return:		status code
>   */
> -static efi_status_t EFIAPI efi_set_virtual_address_map(
> +static __efi_runtime efi_status_t EFIAPI efi_set_virtual_address_map(
>  			unsigned long memory_map_size,
>  			unsigned long descriptor_size,
>  			uint32_t descriptor_version,
>  			struct efi_mem_desc *virtmap)
>  {
> +	static __efi_runtime_data bool is_patched;
>  	int n = memory_map_size / descriptor_size;
>  	int i;
>  	int rt_code_sections = 0;
>  
> +	if (is_patched)
> +		return EFI_INVALID_PARAMETER;
> +
>  	EFI_ENTRY("%lx %lx %x %p", memory_map_size, descriptor_size,
>  		  descriptor_version, virtmap);
>  
> +	is_patched = true;
> +
>  	/*
>  	 * TODO:
>  	 * Further down we are cheating. While really we should implement
> @@ -514,8 +524,7 @@ static efi_status_t EFIAPI efi_set_virtual_address_map(
>  					   map->physical_start + gd->relocaddr;
>  
>  			efi_runtime_relocate(new_offset, map);
> -			/* Once we're virtual, we can no longer handle
> -			   complex callbacks */
> +			/* We need to repatch callbacks for their new VA */
>  			efi_runtime_detach(new_offset);
>  			return EFI_EXIT(EFI_SUCCESS);
>  		}
>