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Date: Fri, 3 Jul 2020 10:02:55 -0700
From: Andy Lutomirski <luto@...nel.org>
To: x86@...nel.org
Cc: Andrew Cooper <andrew.cooper3@...rix.com>,
Juergen Gross <jgross@...e.com>,
LKML <linux-kernel@...r.kernel.org>,
Andy Lutomirski <luto@...nel.org>
Subject: [PATCH entry v2 3/6] x86/entry/xen: Route #DB correctly on Xen PV
On Xen PV, #DB doesn't use IST. We still need to correctly route it
depending on whether it came from user or kernel mode.
This patch gets 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: 4c0dcd8350a0 ("x86/entry: Implement user mode C entry points for #DB and #MCE")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
arch/x86/include/asm/idtentry.h | 24 ++++++------------------
arch/x86/kernel/traps.c | 12 ++++++++++++
arch/x86/xen/enlighten_pv.c | 28 ++++++++++++++++++++++++----
arch/x86/xen/xen-asm_64.S | 5 ++---
4 files changed, 44 insertions(+), 25 deletions(-)
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index cf51c50eb356..94333ac3092b 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -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);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index f9727b96961f..c17f9b57171f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -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();
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index acc49fa6a097..0d68948c82ad 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -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
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index e1e1c7eafa60..aab1d99b2b48 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -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
--
2.25.4
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