[PATCH 1/4] stack overflow safe kdump (2.6.18-rc1-i386) - safe_smp_processor_id

[PATCH 1/4] stack overflow safe kdump (2.6.18-rc1-i386) - safe_smp_processor_id

[Fernando Luis Vázquez Cao]

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.

Signed-off-by: Fernando Vazquez <fernando@intellilink.co.jp>
---

diff -urNp linux-2.6.18-rc1/arch/i386/kernel/smp.c linux-2.6.18-rc1-sof/arch/i386/kernel/smp.c
--- linux-2.6.18-rc1/arch/i386/kernel/smp.c	2006-07-11 10:11:38.000000000 +0900
+++ linux-2.6.18-rc1-sof/arch/i386/kernel/smp.c	2006-07-11 14:05:28.000000000 +0900
@@ -634,3 +634,29 @@ 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-2.6.18-rc1/include/asm-i386/smp.h linux-2.6.18-rc1-sof/include/asm-i386/smp.h
--- linux-2.6.18-rc1/include/asm-i386/smp.h	2006-07-11 10:11:44.000000000 +0900
+++ linux-2.6.18-rc1-sof/include/asm-i386/smp.h	2006-07-11 14:05:28.000000000 +0900
@@ -89,12 +89,14 @@ 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 */

Re: [PATCH 1/4] stack overflow safe kdump (2.6.18-rc1-i386) - safe_smp_processor_id

[Andrew Morton]

On Tue, 11 Jul 2006 15:05:18 +0900
Fernando Luis Vázquez Cao <fernando@oss.ntt.co.jp> wrote:
> ...

With CONFIG_SMP=n:

arch/i386/kernel/crash.c: In function 'crash_save_self':
arch/i386/kernel/crash.c:91: warning: implicit declaration of function 'safe_smp_processor_id'

And it fails to link.


> --- linux-2.6.18-rc1/include/asm-i386/smp.h	2006-07-11 10:11:44.000000000 +0900
> +++ linux-2.6.18-rc1-sof/include/asm-i386/smp.h	2006-07-11 14:05:28.000000000 +0900
> @@ -89,12 +89,14 @@ 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 */

The reason for this is that include/linux/smp.h only includes asm/smp.h if
CONFIG_SMP=y.  This is not the cleverest thing we've ever done.

I fixed that in cowardly fashion:


--- a/arch/i386/kernel/crash.c~stack-overflow-safe-kdump-crash_use_safe_smp_processor_id-fix
+++ a/arch/i386/kernel/crash.c
@@ -23,6 +23,7 @@
 #include <asm/hw_irq.h>
 #include <asm/apic.h>
 #include <asm/kdebug.h>
+#include <asm/smp.h>
 
 #include <mach_ipi.h>
 
_

Re: [PATCH 1/4] stack overflow safe kdump (2.6.18-rc1-i386) - safe_smp_processor_id

[Fernando Luis Vázquez Cao]

On Tue, 2006-07-11 at 23:46 -0700, Andrew Morton wrote:
> On Tue, 11 Jul 2006 15:05:18 +0900
> Fernando Luis Vázquez Cao <fernando@oss.ntt.co.jp> wrote:
> > ...
> 
> With CONFIG_SMP=n:
> 
> arch/i386/kernel/crash.c: In function 'crash_save_self':
> arch/i386/kernel/crash.c:91: warning: implicit declaration of function 'safe_smp_processor_id'
> 
> And it fails to link.
Thank you for catching this! I had only tried i386-SMP and voyager-SMP
configurations. I will try several UP configurations and see if it
compiles properly.

Sorry for the trouble.

 - Fernando

> > --- linux-2.6.18-rc1/include/asm-i386/smp.h	2006-07-11 10:11:44.000000000 +0900
> > +++ linux-2.6.18-rc1-sof/include/asm-i386/smp.h	2006-07-11 14:05:28.000000000 +0900
> > @@ -89,12 +89,14 @@ 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 */
> 
> The reason for this is that include/linux/smp.h only includes asm/smp.h if
> CONFIG_SMP=y.  This is not the cleverest thing we've ever done.
> 
> I fixed that in cowardly fashion:
> 
> 
> --- a/arch/i386/kernel/crash.c~stack-overflow-safe-kdump-crash_use_safe_smp_processor_id-fix
> +++ a/arch/i386/kernel/crash.c
> @@ -23,6 +23,7 @@
>  #include <asm/hw_irq.h>
>  #include <asm/apic.h>
>  #include <asm/kdebug.h>
> +#include <asm/smp.h>
>  
>  #include <mach_ipi.h>
>  
> _
>