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

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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: 4c0dcd8350 ("x86/entry: Implement user mode C entry points for #DB and #MCE")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/4163e733cce0b41658e252c6c6b3464f33fdff17.1593795633.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2020-07-03 10:02:55 -07:00 committed by Thomas Gleixner
parent 3c73b81a91
commit f41f082422
4 changed files with 44 additions and 25 deletions
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24
arch/x86/include/asm/idtentry.h
View File

@ -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);

12
arch/x86/kernel/traps.c
View File

@ -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();

28
arch/x86/xen/enlighten_pv.c
View File

@ -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

5
arch/x86/xen/xen-asm_64.S
View File

@ -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