Re: [RFC PATCH 1/2] arm64: Add pre-shutdown hook to machine_shutdown()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly introduced global function pointer `arm64_pre_smp_shutdown_hook` is placed in writable memory without the `__ro_after_init` annotation, creating a potential target for control-flow hijacking.
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--- Patch [1]: [RFC PATCH 1/2] arm64: Add pre-shutdown hook to machine_shutdown() ---
commit 438763f14354dbd91b5fa7bea807c334ada0c642
Author: Shradha Gupta <shradhagupta@linux.microsoft.com>

arm64: Add pre-shutdown hook to machine_shutdown()

This patch introduces a global function pointer invoked from
machine_shutdown() to allow platform-specific cleanup before secondary CPUs
go offline during kexec or reboot.

[ ... ]

> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 581f80e9b9b73..41c0e98409138 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -88,8 +88,21 @@ void __noreturn arch_cpu_idle_dead(void)

[ ... ]

> +/*
> + * Hook for platform code to perform cleanup after device_shutdown()
> + * but before secondary CPUs are offlined. This runs in the kexec path
> + * from kernel_kexec() after device_shutdown() and cpu_hotplug_enable()
> + * have been called, matching the point at which x86 invokes
> + * machine_ops.shutdown.
> + */
> +void (*arm64_pre_smp_shutdown_hook)(void);

[Severity: Medium]
Should this global function pointer be annotated with __ro_after_init?

Without it, the pointer resides in writable memory, which could make it a
reliable target for control-flow hijacking if an arbitrary memory write
primitive is obtained elsewhere. Since the hook is presumably only set once
during platform initialization, making it read-only after init would improve
defense-in-depth on the shutdown/reboot path.

> +
>  void machine_shutdown(void)
>  {
> +	if (arm64_pre_smp_shutdown_hook)
> +		arm64_pre_smp_shutdown_hook();
> +
>  	smp_shutdown_nonboot_cpus(reboot_cpu);
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/20260814093133.3191250-1-shradhagupta@linux.microsoft.com?part=1