Re: [PATCH 1/5] stack overflow safe kdump (2.6.15-i386) - safe_smp_processor_id

[Vivek Goyal <vgoyal@in.ibm.com>]

On Mon, Jan 16, 2006 at 10:23:44PM +0900, Fernando Luis Vazquez Cao wrote:
> On the event of a stack overflow critical data that usually resides at
> the bottom of the stack is likely to be stomped and, consequently, its
> use should be avoided.
> 
> In particular, in the i386 and IA64 architectures the macro
> smp_processor_id ultimately makes use of the "cpu" member of struct
> thread_info which resides at the bottom of the stack. x86_64, on the
> other hand, is not affected by this problem because it benefits from
> the use of the PDA infrastructure.
> 
> To circumvent this problem I suggest implementing
> "safe_smp_processor_id()" (it already exists in x86_64) for i386 and
> IA64 and use it as a replacement for smp_processor_id in the reboot path
> to the dump capture kernel. This is a possible implementation for i386.
> 

Acked-by: Vivek Goyal <vgoyal@in.ibm.com>

> ---
> diff -urNp linux-2.6.15/arch/i386/kernel/smp.c
> linux-2.6.15-sov/arch/i386/kernel/smp.c
> --- linux-2.6.15/arch/i386/kernel/smp.c	2006-01-03 12:21:10.000000000
> +0900
> +++ linux-2.6.15-sov/arch/i386/kernel/smp.c	2006-01-16
> 20:25:50.000000000 +0900
> @@ -628,3 +628,28 @@ fastcall void smp_call_function_interrup
>  	}
>  }
>  
> +static int convert_apicid_to_cpu(int apic_id)
> +{
> +	int i;
> +
> +	for (i = 0; i < NR_CPUS; i++) {
> +		if (x86_cpu_to_apicid[i] == apic_id)
> +		return i;
> +	}
> +	return -1;
> +}
> +
> +int safe_smp_processor_id(void) {
> +	int apicid, cpuid;
> +
> +	if (!boot_cpu_has(X86_FEATURE_APIC))
> +		return 0;
> +
> +	apicid = hard_smp_processor_id();
> +	if (apicid == BAD_APICID)
> +		return 0;
> +
> +	cpuid = convert_apicid_to_cpu(apicid);
> +
> +	return cpuid >= 0 ? cpuid : 0;
> +}
> diff -urNp linux-2.6.15/include/asm-i386/smp.h
> linux-2.6.15-sov/include/asm-i386/smp.h
> --- linux-2.6.15/include/asm-i386/smp.h	2006-01-03 12:21:10.000000000
> +0900
> +++ linux-2.6.15-sov/include/asm-i386/smp.h	2006-01-16
> 20:25:50.000000000 +0900
> @@ -90,12 +90,14 @@ static __inline int logical_smp_processo
>  
>  #endif
>  
> +extern int safe_smp_processor_id(void);
>  extern int __cpu_disable(void);
>  extern void __cpu_die(unsigned int cpu);
>  #endif /* !__ASSEMBLY__ */
>  
>  #else /* CONFIG_SMP */
>  
> +#define safe_smp_processor_id() 0
>  #define cpu_physical_id(cpu)		boot_cpu_physical_apicid
>  
>  #define NO_PROC_ID		0xFF		/* No processor magic marker */
> 
>