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From: Ard Biesheuvel <ardb@kernel.org>
Date: Fri, 12 Jan 2024 19:51:16 +0100
Message-ID: <CAMj1kXHUAQVrzdqFXDX1Fid38Gov3R-DNwJSSXXNqVgJPr6cBw@mail.gmail.com>
Subject: Re: [PATCH] riscv/efistub: Ensure GP-relative addressing is not used
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>, linux-efi <linux-efi@vger.kernel.org>, 
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Jan,

On Fri, 12 Jan 2024 at 19:37, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>
> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> The cflags for the RISC-V efistub were missing -mno-relax, thus were
> under the risk that the compiler could use GP-relative addressing. That
> happened for _edata with binutils-2.41 and kernel 6.1, causing the
> relocation to fail due to an invalid kernel_size in handle_kernel_image.
> It was not yet observed with newer versions, but that may just be luck.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>
> Something like this should go to stable as well, but we will need
> rebased patches.
>
>  drivers/firmware/efi/libstub/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 06964a3c130f..d561d7de46a9 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -28,7 +28,7 @@ cflags-$(CONFIG_ARM)          += -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
>                                    -DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
>                                    -DEFI_HAVE_STRCMP -fno-builtin -fpic \
>                                    $(call cc-option,-mno-single-pic-base)
> -cflags-$(CONFIG_RISCV)         += -fpic -DNO_ALTERNATIVE
> +cflags-$(CONFIG_RISCV)         += -fpic -DNO_ALTERNATIVE -mno-relax

Can we detect the presence of these references (via the relocation
type)? We already do something similar for ordinary absolute
references too.

>  cflags-$(CONFIG_LOONGARCH)     += -fpie
>
>  cflags-$(CONFIG_EFI_PARAMS_FROM_FDT)   += -I$(srctree)/scripts/dtc/libfdt
> --
> 2.35.3