Commit d8ba61ba authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner
Browse files

x86/entry/64: Don't use IST entry for #BP stack 



There's nothing IST-worthy about #BP/int3.  We don't allow kprobes
in the small handful of places in the kernel that run at CPL0 with
an invalid stack, and 32-bit kernels have used normal interrupt
gates for #BP forever.

Furthermore, we don't allow kprobes in places that have usergs while
in kernel mode, so "paranoid" is also unnecessary.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
parent 06ace26f

arch/x86/entry/entry_64.S

+1 −1
Original line number Diff line number Diff line
@@ -1138,7 +1138,7 @@ apicinterrupt3 HYPERV_REENLIGHTENMENT_VECTOR \ 
#endif /* CONFIG_HYPERV */



idtentry debug			do_debug		has_error_code=0	paranoid=1 shift_ist=DEBUG_STACK

idtentry int3			do_int3			has_error_code=0	paranoid=1 shift_ist=DEBUG_STACK

idtentry int3			do_int3			has_error_code=0

idtentry stack_segment		do_stack_segment	has_error_code=1



#ifdef CONFIG_XEN

arch/x86/kernel/idt.c

+0 −2
Original line number Diff line number Diff line
@@ -160,7 +160,6 @@ static const __initconst struct idt_data early_pf_idts[] = { 
 */

static const __initconst struct idt_data dbg_idts[] = {

	INTG(X86_TRAP_DB,	debug),

	INTG(X86_TRAP_BP,	int3),

};

#endif
@@ -183,7 +182,6 @@ gate_desc debug_idt_table[IDT_ENTRIES] __page_aligned_bss; 
static const __initconst struct idt_data ist_idts[] = {

	ISTG(X86_TRAP_DB,	debug,		DEBUG_STACK),

	ISTG(X86_TRAP_NMI,	nmi,		NMI_STACK),

	SISTG(X86_TRAP_BP,	int3,		DEBUG_STACK),

	ISTG(X86_TRAP_DF,	double_fault,	DOUBLEFAULT_STACK),

#ifdef CONFIG_X86_MCE

	ISTG(X86_TRAP_MC,	&machine_check,	MCE_STACK),

arch/x86/kernel/traps.c

+8 −7
Original line number Diff line number Diff line
@@ -577,7 +577,6 @@ do_general_protection(struct pt_regs *regs, long error_code) 
}

NOKPROBE_SYMBOL(do_general_protection);



/* May run on IST stack. */

dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)

{

#ifdef CONFIG_DYNAMIC_FTRACE
@@ -592,6 +591,13 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) 
	if (poke_int3_handler(regs))

		return;



	/*

	 * Use ist_enter despite the fact that we don't use an IST stack.

	 * We can be called from a kprobe in non-CONTEXT_KERNEL kernel

	 * mode or even during context tracking state changes.

	 *

	 * This means that we can't schedule.  That's okay.

	 */

	ist_enter(regs);

	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");

#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
@@ -609,15 +615,10 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) 
			SIGTRAP) == NOTIFY_STOP)

		goto exit;



	/*

	 * Let others (NMI) know that the debug stack is in use

	 * as we may switch to the interrupt stack.

	 */

	debug_stack_usage_inc();

	cond_local_irq_enable(regs);

	do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL);

	cond_local_irq_disable(regs);

	debug_stack_usage_dec();



exit:

	ist_exit(regs);

}

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