Messages in this thread Patch in this message |  | | | Subject | [PATCH 4/5] stack overflow safe kdump (2.6.15-i386) - nmi handler and trap vector replacement | | From | Fernando Luis Vazquez Cao <> | | Date | Mon, 16 Jan 2006 22:25:04 +0900 |
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In the nmi path, we have the problem that both nmi_enter and nmi_exit in do_nmi (see code below) make extensive use of "current" (which might be invalid) indirectly (specially through the kernel preemption code). Create a new nmi trap handler robust against stack overflows and use it on the crash dump path.
--- diff -urNp linux-2.6.15/arch/i386/kernel/crash.c linux-2.6.15-sov/arch/i386/kernel/crash.c --- linux-2.6.15/arch/i386/kernel/crash.c 2006-01-16 20:29:50.000000000 +0900 +++ linux-2.6.15-sov/arch/i386/kernel/crash.c 2006-01-16 20:33:55.000000000 +0900 @@ -22,6 +22,7 @@ #include <asm/nmi.h> #include <asm/hw_irq.h> #include <asm/apic.h> +#include <mach_traps.h> #include <mach_ipi.h> @@ -142,6 +143,7 @@ static int crash_nmi_callback(struct pt_ if (cpu == crashing_cpu) return 1; local_irq_disable(); + disable_nmi(); if (!user_mode(regs)) { crash_setup_regs(&fixed_regs, regs); @@ -167,13 +169,18 @@ static void smp_send_nmi_allbutself(void send_IPI_allbutself(APIC_DM_NMI); } +static void set_crash_nmi(void) +{ + set_crash_nmi_callback(crash_nmi_callback); +} + static void nmi_shootdown_cpus(void) { unsigned long msecs; atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1); - /* Would it be better to replace the trap vector here? */ - set_nmi_callback(crash_nmi_callback); + /* Set the nmi handler appropriately for the crash case */ + set_crash_nmi(); /* Ensure the new callback function is set before sending * out the NMI */ diff -urNp linux-2.6.15/arch/i386/kernel/entry.S linux-2.6.15-sov/arch/i386/kernel/entry.S --- linux-2.6.15/arch/i386/kernel/entry.S 2006-01-03 12:21:10.000000000 +0900 +++ linux-2.6.15-sov/arch/i386/kernel/entry.S 2006-01-16 21:52:24.000000000 +0900 @@ -590,6 +590,41 @@ nmi_16bit_stack: .long 1b,iret_exc .previous +ENTRY(crash_nmi) + pushl %eax + movl %ss, %eax + cmpw $__ESPFIX_SS, %ax + popl %eax + je crash_nmi_16bit_stack + pushl %eax + SAVE_ALL + xorl %edx,%edx # zero error code + movl %esp,%eax # pt_regs pointer + call do_crash_nmi + jmp restore_all +crash_nmi_16bit_stack: + /* create the pointer to lss back */ + pushl %ss + pushl %esp + movzwl %sp, %esp + addw $4, (%esp) + /* copy the iret frame of 12 bytes */ + .rept 3 + pushl 16(%esp) + .endr + pushl %eax + SAVE_ALL + FIXUP_ESPFIX_STACK # %eax == %esp + xorl %edx,%edx # zero error code + call do_crash_nmi + RESTORE_REGS + lss 12+4(%esp), %esp # back to 16bit stack +1: iret +.section __ex_table,"a" + .align 4 + .long 1b,iret_exc +.previous + KPROBE_ENTRY(int3) pushl $-1 # mark this as an int SAVE_ALL diff -urNp linux-2.6.15/arch/i386/kernel/traps.c linux-2.6.15-sov/arch/i386/kernel/traps.c --- linux-2.6.15/arch/i386/kernel/traps.c 2006-01-03 12:21:10.000000000 +0900 +++ linux-2.6.15-sov/arch/i386/kernel/traps.c 2006-01-16 20:51:31.000000000 +0900 @@ -74,6 +74,7 @@ struct desc_struct idt_table[256] __attr asmlinkage void divide_error(void); asmlinkage void debug(void); asmlinkage void nmi(void); +asmlinkage void crash_nmi(void); asmlinkage void int3(void); asmlinkage void overflow(void); asmlinkage void bounds(void); @@ -641,23 +642,37 @@ static int dummy_nmi_callback(struct pt_ } static nmi_callback_t nmi_callback = dummy_nmi_callback; - -fastcall void do_nmi(struct pt_regs * regs, long error_code) + +static fastcall unsigned int __do_nmi(struct pt_regs * regs, long error_code) { int cpu; - nmi_enter(); - - cpu = smp_processor_id(); + cpu = safe_smp_processor_id(); ++nmi_count(cpu); if (!rcu_dereference(nmi_callback)(regs, cpu)) default_do_nmi(regs); + return 0; +} + +#define _do_nmi(regs, error_code, nmih) nmih(regs, error_code); + +fastcall void do_nmi(struct pt_regs * regs, long error_code) +{ + nmi_enter(); + + _do_nmi(regs, error_code, __do_nmi); + nmi_exit(); } +fastcall void do_crash_nmi(struct pt_regs * regs, long error_code) +{ + _do_nmi(regs, error_code, __do_nmi); +} + void set_nmi_callback(nmi_callback_t callback) { rcu_assign_pointer(nmi_callback, callback); @@ -670,6 +685,17 @@ void unset_nmi_callback(void) } EXPORT_SYMBOL_GPL(unset_nmi_callback); +void set_crash_nmi_callback(nmi_callback_t callback) +{ + /* XXX Do we need to do this atomically? */ + disable_nmi(); + unset_nmi_callback(); + /* Replace the trap vector */ + set_intr_gate(2,&crash_nmi); + rcu_assign_pointer(nmi_callback, callback); +} +EXPORT_SYMBOL_GPL(set_crash_nmi_callback); + #ifdef CONFIG_KPROBES fastcall void __kprobes do_int3(struct pt_regs *regs, long error_code) { diff -urNp linux-2.6.15/include/asm-i386/mach-default/mach_traps.h linux-2.6.15-sov/include/asm-i386/mach-default/mach_traps.h --- linux-2.6.15/include/asm-i386/mach-default/mach_traps.h 2006-01-03 12:21:10.000000000 +0900 +++ linux-2.6.15-sov/include/asm-i386/mach-default/mach_traps.h 2006-01-16 20:33:55.000000000 +0900 @@ -20,6 +20,11 @@ static inline unsigned char get_nmi_reas return inb(0x61); } +static inline void disable_nmi(void) +{ + outb(0x8f, 0x70); +} + static inline void reassert_nmi(void) { int old_reg = -1; diff -urNp linux-2.6.15/include/asm-i386/nmi.h linux-2.6.15-sov/include/asm-i386/nmi.h --- linux-2.6.15/include/asm-i386/nmi.h 2006-01-03 12:21:10.000000000 +0900 +++ linux-2.6.15-sov/include/asm-i386/nmi.h 2006-01-16 20:33:55.000000000 +0900 @@ -17,6 +17,7 @@ typedef int (*nmi_callback_t)(struct pt_ * set. Return 1 if the NMI was handled. */ void set_nmi_callback(nmi_callback_t callback); +void set_crash_nmi_callback(nmi_callback_t callback); /** * unset_nmi_callback
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