[PATCH] efi/libstub/x86: deal with exit() boot service returning

[PATCH] efi/libstub/x86: deal with exit() boot service returning

[Ard Biesheuvel]

Even though it is uncommon, there are cases where the Exit() EFI boot
service might return, e.g., when we were booted via the EFI handover
protocol from OVMF and the kernel image was specified on the command
line, in which case Exit() attempts to terminate the boot manager,
which is not an EFI application itself. So let's drop into a deadloop
instead.

Cc: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
As a side effect, this also fixes [0], which is as yet undiagnosed.

[0] https://github.com/ClangBuiltLinux/linux/issues/917

 drivers/firmware/efi/libstub/x86-stub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 7f3e97c2aad3..5c7480c4d379 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -344,7 +344,7 @@ static void setup_graphics(struct boot_params *boot_params)
 static void __noreturn efi_exit(efi_handle_t handle, efi_status_t status)
 {
 	efi_bs_call(exit, handle, status, 0, NULL);
-	unreachable();
+	for(;;);
 }
 
 void startup_32(struct boot_params *boot_params);
-- 
2.17.1

Re: [PATCH] efi/libstub/x86: deal with exit() boot service returning

[Nathan Chancellor]

On Tue, Mar 03, 2020 at 09:06:48AM +0100, Ard Biesheuvel wrote:
> Even though it is uncommon, there are cases where the Exit() EFI boot
> service might return, e.g., when we were booted via the EFI handover
> protocol from OVMF and the kernel image was specified on the command
> line, in which case Exit() attempts to terminate the boot manager,
> which is not an EFI application itself. So let's drop into a deadloop
> instead.
> 
> Cc: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> As a side effect, this also fixes [0], which is as yet undiagnosed.
> 
> [0] https://github.com/ClangBuiltLinux/linux/issues/917

And for that:

Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build

>  drivers/firmware/efi/libstub/x86-stub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> index 7f3e97c2aad3..5c7480c4d379 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -344,7 +344,7 @@ static void setup_graphics(struct boot_params *boot_params)
>  static void __noreturn efi_exit(efi_handle_t handle, efi_status_t status)
>  {
>  	efi_bs_call(exit, handle, status, 0, NULL);
> -	unreachable();
> +	for(;;);

I thought this would have tripped up clang's -Wempty-body but it
doesn't so that is good.

>  }
>  
>  void startup_32(struct boot_params *boot_params);
> -- 
> 2.17.1
>