Commit f41f0824 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner
Browse files

x86/entry/xen: Route #DB correctly on Xen PV 



On Xen PV, #DB doesn't use IST. It still needs to be correctly routed
depending on whether it came from user or kernel mode.

Get rid of DECLARE/DEFINE_IDTENTRY_XEN -- it was too hard to follow the
logic.  Instead, route #DB and NMI through DECLARE/DEFINE_IDTENTRY_RAW on
Xen, and do the right thing for #DB.  Also add more warnings to the
exc_debug* handlers to make this type of failure more obvious.

This fixes various forms of corruption that happen when usermode
triggers #DB on Xen PV.

Fixes: 4c0dcd83 ("x86/entry: Implement user mode C entry points for #DB and #MCE")
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/4163e733cce0b41658e252c6c6b3464f33fdff17.1593795633.git.luto@kernel.org
parent 3c73b81a

arch/x86/include/asm/idtentry.h

+6 −18
Original line number Diff line number Diff line
@@ -398,18 +398,6 @@ __visible noinstr void func(struct pt_regs *regs, \ 
#define DEFINE_IDTENTRY_DEBUG		DEFINE_IDTENTRY_IST

#define DEFINE_IDTENTRY_DEBUG_USER	DEFINE_IDTENTRY_NOIST



/**

 * DECLARE_IDTENTRY_XEN - Declare functions for XEN redirect IDT entry points

 * @vector:	Vector number (ignored for C)

 * @func:	Function name of the entry point

 *

 * Used for xennmi and xendebug redirections. No DEFINE as this is all ASM

 * indirection magic.

 */

#define DECLARE_IDTENTRY_XEN(vector, func)				\

	asmlinkage void xen_asm_exc_xen##func(void);			\

	asmlinkage void asm_exc_xen##func(void)



#else /* !__ASSEMBLY__ */



/*
@@ -469,10 +457,6 @@ __visible noinstr void func(struct pt_regs *regs, \ 
/* No ASM code emitted for NMI */

#define DECLARE_IDTENTRY_NMI(vector, func)



/* XEN NMI and DB wrapper */

#define DECLARE_IDTENTRY_XEN(vector, func)				\

	idtentry vector asm_exc_xen##func exc_##func has_error_code=0



/*

 * ASM code to emit the common vector entry stubs where each stub is

 * packed into 8 bytes.
@@ -570,11 +554,15 @@ DECLARE_IDTENTRY_MCE(X86_TRAP_MC, exc_machine_check); 


/* NMI */

DECLARE_IDTENTRY_NMI(X86_TRAP_NMI,	exc_nmi);

DECLARE_IDTENTRY_XEN(X86_TRAP_NMI,	nmi);

#ifdef CONFIG_XEN_PV

DECLARE_IDTENTRY_RAW(X86_TRAP_NMI,	xenpv_exc_nmi);

#endif



/* #DB */

DECLARE_IDTENTRY_DEBUG(X86_TRAP_DB,	exc_debug);

DECLARE_IDTENTRY_XEN(X86_TRAP_DB,	debug);

#ifdef CONFIG_XEN_PV

DECLARE_IDTENTRY_RAW(X86_TRAP_DB,	xenpv_exc_debug);

#endif



/* #DF */

DECLARE_IDTENTRY_DF(X86_TRAP_DF,	exc_double_fault);

arch/x86/kernel/traps.c

+12 −0
Original line number Diff line number Diff line
@@ -865,6 +865,12 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, 
	instrumentation_begin();

	trace_hardirqs_off_finish();



	/*

	 * If something gets miswired and we end up here for a user mode

	 * #DB, we will malfunction.

	 */

	WARN_ON_ONCE(user_mode(regs));



	/*

	 * Catch SYSENTER with TF set and clear DR_STEP. If this hit a

	 * watchpoint at the same time then that will still be handled.
@@ -883,6 +889,12 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, 
static __always_inline void exc_debug_user(struct pt_regs *regs,

					   unsigned long dr6)

{

	/*

	 * If something gets miswired and we end up here for a kernel mode

	 * #DB, we will malfunction.

	 */

	WARN_ON_ONCE(!user_mode(regs));



	idtentry_enter_user(regs);

	instrumentation_begin();

arch/x86/xen/enlighten_pv.c

+24 −4
Original line number Diff line number Diff line
@@ -598,6 +598,26 @@ static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum, 
}



#ifdef CONFIG_X86_64

void noist_exc_debug(struct pt_regs *regs);



DEFINE_IDTENTRY_RAW(xenpv_exc_nmi)

{

	/* On Xen PV, NMI doesn't use IST.  The C part is the sane as native. */

	exc_nmi(regs);

}



DEFINE_IDTENTRY_RAW(xenpv_exc_debug)

{

	/*

	 * There's no IST on Xen PV, but we still need to dispatch

	 * to the correct handler.

	 */

	if (user_mode(regs))

		noist_exc_debug(regs);

	else

		exc_debug(regs);

}



struct trap_array_entry {

	void (*orig)(void);

	void (*xen)(void);
@@ -609,18 +629,18 @@ struct trap_array_entry { 
	.xen		= xen_asm_##func,		\

	.ist_okay	= ist_ok }



#define TRAP_ENTRY_REDIR(func, xenfunc, ist_ok) {	\

#define TRAP_ENTRY_REDIR(func, ist_ok) {		\

	.orig		= asm_##func,			\

	.xen		= xen_asm_##xenfunc,		\

	.xen		= xen_asm_xenpv_##func,		\

	.ist_okay	= ist_ok }



static struct trap_array_entry trap_array[] = {

	TRAP_ENTRY_REDIR(exc_debug, exc_xendebug,	true  ),

	TRAP_ENTRY_REDIR(exc_debug,			true  ),

	TRAP_ENTRY(exc_double_fault,			true  ),

#ifdef CONFIG_X86_MCE

	TRAP_ENTRY(exc_machine_check,			true  ),

#endif

	TRAP_ENTRY_REDIR(exc_nmi, exc_xennmi,		true  ),

	TRAP_ENTRY_REDIR(exc_nmi,			true  ),

	TRAP_ENTRY(exc_int3,				false ),

	TRAP_ENTRY(exc_overflow,			false ),

#ifdef CONFIG_IA32_EMULATION

arch/x86/xen/xen-asm_64.S

+2 −3
Original line number Diff line number Diff line
@@ -29,10 +29,9 @@ _ASM_NOKPROBE(xen_\name) 
.endm



xen_pv_trap asm_exc_divide_error

xen_pv_trap asm_exc_debug

xen_pv_trap asm_exc_xendebug

xen_pv_trap asm_xenpv_exc_debug

xen_pv_trap asm_exc_int3

xen_pv_trap asm_exc_xennmi

xen_pv_trap asm_xenpv_exc_nmi

xen_pv_trap asm_exc_overflow

xen_pv_trap asm_exc_bounds

xen_pv_trap asm_exc_invalid_op

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