Re: [PATCH 2/3] arch: use CONFIG_COMMAND_LINE_SIZE across all architectures

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] RISC-V default command line size is silently truncated from 2048 to 1024 bytes.
- [High] Exposing COMMAND_LINE_SIZE to Kconfig allows deterministic stack exhaustion in the ARM boot decompressor.
- [High] Configurable COMMAND_LINE_SIZE causes stack exhaustion during early boot on m68k Atari.
--

--- Patch [2]: [PATCH 2/3] arch: use CONFIG_COMMAND_LINE_SIZE across all architectures ---
commit 86e4b8b798d614166a3d212659ea7796c8a7ee99
Author: Wilson Felipe Pereira <wfelipe@google.com>

arch: use CONFIG_COMMAND_LINE_SIZE across all architectures

This commit updates every architecture's setup.h to define COMMAND_LINE_SIZE
using CONFIG_COMMAND_LINE_SIZE for the kernel. The historical hardcoded
defaults are retained in user-space API headers by wrapping the definition
in an #ifdef __KERNEL__ guard.

> diff --git a/arch/arm/include/uapi/asm/setup.h b/arch/arm/include/uapi/asm/setup.h
> index 8e50e034fec73..4aa93558af1e7 100644
> --- a/arch/arm/include/uapi/asm/setup.h
> +++ b/arch/arm/include/uapi/asm/setup.h
> @@ -17,7 +17,11 @@
>  
>  #include <linux/types.h>
>  
> -#define COMMAND_LINE_SIZE 1024
> +#ifdef __KERNEL__
> +#define COMMAND_LINE_SIZE	CONFIG_COMMAND_LINE_SIZE
> +#else
> +#define COMMAND_LINE_SIZE	1024
> +#endif

[Severity: High]
Does exposing COMMAND_LINE_SIZE to Kconfig allow deterministic stack exhaustion
in the ARM boot decompressor?

The ARM boot decompressor uses a fixed 4KB stack (.L_user_stack in
arch/arm/boot/compressed/head.S), and merge_fdt_bootargs() allocates:

arch/arm/boot/compressed/atags_to_fdt.c:merge_fdt_bootargs() {
    ...
	char cmdline[COMMAND_LINE_SIZE];
    ...
}

If a user configures CONFIG_COMMAND_LINE_SIZE to a value larger than ~3KB,
will this stack allocation deterministically crash on boot?

[ ... ]

> diff --git a/arch/m68k/include/uapi/asm/setup.h b/arch/m68k/include/uapi/asm/setup.h
> index 25fe26d5597cc..2d5b24a5345f9 100644
> --- a/arch/m68k/include/uapi/asm/setup.h
> +++ b/arch/m68k/include/uapi/asm/setup.h
> @@ -12,6 +12,10 @@
>  #ifndef _UAPI_M68K_SETUP_H
>  #define _UAPI_M68K_SETUP_H
>  
> -#define COMMAND_LINE_SIZE 256
> +#ifdef __KERNEL__
> +#define COMMAND_LINE_SIZE	CONFIG_COMMAND_LINE_SIZE
> +#else
> +#define COMMAND_LINE_SIZE	256
> +#endif

[Severity: High]
Can a configurable COMMAND_LINE_SIZE cause stack exhaustion during early boot
on m68k Atari?

atari_switches_setup() allocates an array locally on the limited kernel stack:

arch/m68k/atari/config.c:atari_switches_setup() {
    ...
	char switches[COMMAND_LINE_SIZE];
    ...
}

Will tying this to an unbound Kconfig option introduce deterministic stack
exhaustion on boot for m68k Atari kernels?

[ ... ]

> diff --git a/arch/riscv/include/uapi/asm/setup.h b/arch/riscv/include/uapi/asm/setup.h
> index eb4f0209c6960..a6c1f4b0987e3 100644
> --- a/arch/riscv/include/uapi/asm/setup.h
> +++ b/arch/riscv/include/uapi/asm/setup.h
> @@ -3,6 +3,10 @@
>  #ifndef _UAPI_ASM_RISCV_SETUP_H
>  #define _UAPI_ASM_RISCV_SETUP_H
>  
> +#ifdef __KERNEL__
> +#define COMMAND_LINE_SIZE	CONFIG_COMMAND_LINE_SIZE
> +#else
>  #define COMMAND_LINE_SIZE	2048
> +#endif

[Severity: High]
Is the RISC-V default command line size silently truncated from 2048 to 1024
bytes?

The Kconfig default in init/Kconfig erroneously groups RISC-V with ARM and
PARISC (1024):

init/Kconfig:
	default 1024 if ARM || PARISC || RISCV

By replacing the kernel definition with CONFIG_COMMAND_LINE_SIZE here, does
this create a dangerous discrepancy where userspace headers claim the limit
is 2048, while the kernel internally enforces 1024 and truncates existing
boot configurations?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806061429.474992-1-wfelipe@google.com?part=2