From dc2bc768a009b9ad8711894c544dc6b0d8c0ce57 Mon Sep 17 00:00:00 2001 From: Fernando Vazquez Date: Sat, 30 Sep 2006 23:29:07 -0700 Subject: [PATCH] [PATCH] stack overflow safe kdump: safe_smp_processor_id() This is a the first of a series of patch-sets aiming at making kdump more robust against stack overflows. This patch set does the following: * Add safe_smp_processor_id function to i386 architecture (this function was inspired by the x86_64 function of the same name). * Substitute "smp_processor_id" with the stack overflow-safe "safe_smp_processor_id" in the reboot path to the second kernel. This patch: 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 Looks-reasonable-to: Andi Kleen Acked-by: "Eric W. Biederman" Cc: Vivek Goyal Cc: James Bottomley Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/smp.c | 27 +++++++++++++++++++++++++++ include/asm-i386/smp.h | 2 ++ 2 files changed, 29 insertions(+) diff --git a/arch/i386/kernel/smp.c b/arch/i386/kernel/smp.c index 465188e2d701..1b080ab8a49f 100644 --- a/arch/i386/kernel/smp.c +++ b/arch/i386/kernel/smp.c @@ -700,3 +700,30 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info, return 0; } EXPORT_SYMBOL(smp_call_function_single); + +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 --git a/include/asm-i386/smp.h b/include/asm-i386/smp.h index 915c26a31b79..6aa1206f6e2a 100644 --- a/include/asm-i386/smp.h +++ b/include/asm-i386/smp.h @@ -84,6 +84,7 @@ static inline int hard_smp_processor_id(void) #endif #endif +extern int safe_smp_processor_id(void); extern int __cpu_disable(void); extern void __cpu_die(unsigned int cpu); extern unsigned int num_processors; @@ -92,6 +93,7 @@ extern unsigned int num_processors; #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 */ -- 2.30.2