Re: [PATCH] LoongArch: kexec: Fix address space mismatch in command line lookup

[Huacai Chen]

Hi, George,

On Fri, Jun 26, 2026 at 6:52 PM George Guo <dongtai.guo@xxxxxxxxx> wrote:
>
> From: George Guo <guodongtai@xxxxxxxxxx>
>
> When searching the loaded segments for the "kexec" command line marker,
> the kexec_load(2) path (file_mode == 0) passes the user-space segment
> buffer straight to strncmp() through a bogus (char __user *) cast. This
> dereferences a user pointer in kernel context, which is wrong and is
> flagged by sparse:
>
>   arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in
>   argument 2 (different address spaces) @@ expected char const * @@ got
>   char [noderef] __user *
>
> Copy the marker-sized prefix of each segment into a small on-stack
> buffer with copy_from_user() before comparing, and skip segments that
> fault. The subsequent copy_from_user() that stages the full command line
> into the safe area is left unchanged.
>
> Fixes: 4a03b2ac06a5 ("LoongArch: Add kexec support")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605051639.aEPioXdD-lkp@xxxxxxxxx/
> Co-developed-by: Kexin Liu <liukexin@xxxxxxxxxx>
> Signed-off-by: Kexin Liu <liukexin@xxxxxxxxxx>
> Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
> ---
>  arch/loongarch/kernel/machine_kexec.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> index d7fafda1d541..6f563175ddbf 100644
> --- a/arch/loongarch/kernel/machine_kexec.c
> +++ b/arch/loongarch/kernel/machine_kexec.c
> @@ -42,7 +42,7 @@ static unsigned long first_ind_entry;
>  int machine_kexec_prepare(struct kimage *kimage)
>  {
>         int i;
> -       char *bootloader = "kexec";
> +       static const char bootloader[] = "kexec";
>         void *cmdline_ptr = (void *)KEXEC_CMDLINE_ADDR;
>
>         kimage->arch.efi_boot = fw_arg0;
> @@ -57,9 +57,13 @@ int machine_kexec_prepare(struct kimage *kimage)
>                                         strlen((char *)kimage->arch.cmdline_ptr) + 1);
>                 kimage->arch.cmdline_ptr = (unsigned long)KEXEC_CMDLINE_ADDR;
>         } else {
> +               char tmp[sizeof(bootloader)];
Just define it as "head[8]" near bootloader, and bootloader is
unnecessary to modify.

Huacai

> +
>                 /* Find the command line */
>                 for (i = 0; i < kimage->nr_segments; i++) {
> -                       if (!strncmp(bootloader, (char __user *)kimage->segment[i].buf, strlen(bootloader))) {
> +                       if (copy_from_user(tmp, kimage->segment[i].buf, strlen(bootloader)))
> +                               continue;
> +                       if (!strncmp(bootloader, tmp, strlen(bootloader))) {
>                                 if (!copy_from_user(cmdline_ptr, kimage->segment[i].buf, COMMAND_LINE_SIZE))
>                                         kimage->arch.cmdline_ptr = (unsigned long)cmdline_ptr;
>                                 break;
> --
> 2.25.1
>
>