linux-kernel - Re: [PATCH v2 3/4] LoongArch: Fix entry point in image header

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Date: Wed, 22 May 2024 16:00:29 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: Binbin Zhou <zhoubinbin@...ngson.cn>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 3/4] LoongArch: Fix entry point in image header

Hi, Jiaxun,

On Wed, May 22, 2024 at 2:30 PM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>
> Currently kernel entry in head.S is in DMW address range,
> firmware is instructed to jump to this address after loading
> the image.
>
> However kernel should not make any assumption on firmware's
> DMW setting, thus the entry point should be a physical address
> falls into direct translation region.
>
> Fix by applying a calculation to the entry and amend entry
> calculation logic in libstub accordingly.
>
> Note that due to relocation restriction TO_PHYS can't be used
> in assembly, we can only do plus and minus here.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
> v2: Fix efistub
> ---
>  arch/loongarch/kernel/head.S             | 2 +-
>  drivers/firmware/efi/libstub/loongarch.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index c4f7de2e2805..1a83564023e1 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -22,7 +22,7 @@
>  _head:
>         .word   MZ_MAGIC                /* "MZ", MS-DOS header */
>         .org    0x8
> -       .dword  kernel_entry            /* Kernel entry point */
> +       .dword  PHYS_LINK_KADDR + (kernel_entry - _head)        /* Kernel entry point */
It could be better to calculate it in the link script, just as _kernel_asize.

Huacai

>         .dword  _kernel_asize           /* Kernel image effective size */
>         .quad   PHYS_LINK_KADDR         /* Kernel image load offset from start of RAM */
>         .org    0x38                    /* 0x20 ~ 0x37 reserved */
> diff --git a/drivers/firmware/efi/libstub/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
> index 684c9354637c..60c145121393 100644
> --- a/drivers/firmware/efi/libstub/loongarch.c
> +++ b/drivers/firmware/efi/libstub/loongarch.c
> @@ -41,7 +41,7 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map, void *priv)
>  unsigned long __weak kernel_entry_address(unsigned long kernel_addr,
>                 efi_loaded_image_t *image)
>  {
> -       return *(unsigned long *)(kernel_addr + 8) - VMLINUX_LOAD_ADDRESS + kernel_addr;
> +       return *(unsigned long *)(kernel_addr + 8) - TO_PHYS(VMLINUX_LOAD_ADDRESS) + kernel_addr;
>  }
>
>  efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
>
> --
> 2.43.0
>
>