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Commit 228bdaa9 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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x86: Keep current stack in NMI breakpoints 



We want to allow NMI handlers to have breakpoints to be able to
remove stop_machine from ftrace, kprobes and jump_labels. But if
an NMI interrupts a current breakpoint, and then it triggers a
breakpoint itself, it will switch to the breakpoint stack and
corrupt the data on it for the breakpoint processing that it
interrupted.

Instead, have the NMI check if it interrupted breakpoint processing
by checking if the stack that is currently used is a breakpoint
stack. If it is, then load a special IDT that changes the IST
for the debug exception to keep the same stack in kernel context.
When the NMI is done, it puts it back.

This way, if the NMI does trigger a breakpoint, it will keep
using the same stack and not stomp on the breakpoint data for
the breakpoint it interrupted.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 3f3c8b8c

arch/x86/include/asm/desc.h

+12 −0
Original line number Diff line number Diff line
@@ -35,6 +35,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in 


extern struct desc_ptr idt_descr;

extern gate_desc idt_table[];

extern struct desc_ptr nmi_idt_descr;

extern gate_desc nmi_idt_table[];



struct gdt_page {

	struct desc_struct gdt[GDT_ENTRIES];
@@ -307,6 +309,16 @@ static inline void set_desc_limit(struct desc_struct *desc, unsigned long limit) 
	desc->limit = (limit >> 16) & 0xf;

}



#ifdef CONFIG_X86_64

static inline void set_nmi_gate(int gate, void *addr)

{

	gate_desc s;



	pack_gate(&s, GATE_INTERRUPT, (unsigned long)addr, 0, 0, __KERNEL_CS);

	write_idt_entry(nmi_idt_table, gate, &s);

}

#endif



static inline void _set_gate(int gate, unsigned type, void *addr,

			     unsigned dpl, unsigned ist, unsigned seg)

{

arch/x86/include/asm/processor.h

+6 −0
Original line number Diff line number Diff line
@@ -402,6 +402,9 @@ DECLARE_PER_CPU(char *, irq_stack_ptr); 
DECLARE_PER_CPU(unsigned int, irq_count);

extern unsigned long kernel_eflags;

extern asmlinkage void ignore_sysret(void);

int is_debug_stack(unsigned long addr);

void debug_stack_set_zero(void);

void debug_stack_reset(void);

#else	/* X86_64 */

#ifdef CONFIG_CC_STACKPROTECTOR

/*
@@ -416,6 +419,9 @@ struct stack_canary { 
};

DECLARE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);

#endif

static inline int is_debug_stack(unsigned long addr) { return 0; }

static inline void debug_stack_set_zero(void) { }

static inline void debug_stack_reset(void) { }

#endif	/* X86_64 */



extern unsigned int xstate_size;

arch/x86/kernel/cpu/common.c

+22 −0
Original line number Diff line number Diff line
@@ -1026,6 +1026,8 @@ __setup("clearcpuid=", setup_disablecpuid); 


#ifdef CONFIG_X86_64

struct desc_ptr idt_descr = { NR_VECTORS * 16 - 1, (unsigned long) idt_table };

struct desc_ptr nmi_idt_descr = { NR_VECTORS * 16 - 1,

				    (unsigned long) nmi_idt_table };



DEFINE_PER_CPU_FIRST(union irq_stack_union,

		     irq_stack_union) __aligned(PAGE_SIZE);
@@ -1090,6 +1092,24 @@ unsigned long kernel_eflags; 
 */

DEFINE_PER_CPU(struct orig_ist, orig_ist);



static DEFINE_PER_CPU(unsigned long, debug_stack_addr);



int is_debug_stack(unsigned long addr)

{

	return addr <= __get_cpu_var(debug_stack_addr) &&

		addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ);

}



void debug_stack_set_zero(void)

{

	load_idt((const struct desc_ptr *)&nmi_idt_descr);

}



void debug_stack_reset(void)

{

	load_idt((const struct desc_ptr *)&idt_descr);

}



#else	/* CONFIG_X86_64 */



DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
@@ -1208,6 +1228,8 @@ void __cpuinit cpu_init(void) 
			estacks += exception_stack_sizes[v];

			oist->ist[v] = t->x86_tss.ist[v] =

					(unsigned long)estacks;

			if (v == DEBUG_STACK-1)

				per_cpu(debug_stack_addr, cpu) = (unsigned long)estacks;

		}

	}

arch/x86/kernel/head_64.S

+4 −0
Original line number Diff line number Diff line
@@ -417,6 +417,10 @@ ENTRY(phys_base) 
ENTRY(idt_table)

	.skip IDT_ENTRIES * 16



	.align L1_CACHE_BYTES

ENTRY(nmi_idt_table)

	.skip IDT_ENTRIES * 16



	__PAGE_ALIGNED_BSS

	.align PAGE_SIZE

ENTRY(empty_zero_page)

arch/x86/kernel/nmi.c

+15 −0
Original line number Diff line number Diff line
@@ -408,6 +408,18 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs) 
dotraplinkage notrace __kprobes void

do_nmi(struct pt_regs *regs, long error_code)

{

	int update_debug_stack = 0;



	/*

	 * If we interrupted a breakpoint, it is possible that

	 * the nmi handler will have breakpoints too. We need to

	 * change the IDT such that breakpoints that happen here

	 * continue to use the NMI stack.

	 */

	if (unlikely(is_debug_stack(regs->sp))) {

		debug_stack_set_zero();

		update_debug_stack = 1;

	}

	nmi_enter();



	inc_irq_stat(__nmi_count);
@@ -416,6 +428,9 @@ do_nmi(struct pt_regs *regs, long error_code) 
		default_do_nmi(regs);



	nmi_exit();



	if (unlikely(update_debug_stack))

		debug_stack_reset();

}



void stop_nmi(void)