From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 28 Aug 2017 08:47:22 +0200
Subject: [PATCH] x86/traps: Simplify pagefault tracing logic
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CVE-2017-5754

Make use of the new irqvector tracing static key and remove the duplicated
trace_do_pagefault() implementation.

If irq vector tracing is disabled, then the overhead of this is a single
NOP5, which is a reasonable tradeoff to avoid duplicated code and the
unholy macro mess.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064956.672965407@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 11a7ffb01703c3bbb1e9b968893f4487a1b0b5a8)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit 8478bb5608747fd64c9fd4a2f5422fb4af756a50)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 arch/x86/include/asm/traps.h | 10 +--------
 arch/x86/kernel/kvm.c        |  2 +-
 arch/x86/mm/fault.c          | 49 ++++++++++++--------------------------------
 arch/x86/entry/entry_32.S    |  8 --------
 arch/x86/entry/entry_64.S    | 13 +-----------
 5 files changed, 16 insertions(+), 66 deletions(-)

diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 01fd0a7f48cd..b4f322d6c95f 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -39,7 +39,6 @@ asmlinkage void machine_check(void);
 asmlinkage void simd_coprocessor_error(void);
 
 #ifdef CONFIG_TRACING
-asmlinkage void trace_page_fault(void);
 #define trace_stack_segment stack_segment
 #define trace_divide_error divide_error
 #define trace_bounds bounds
@@ -54,6 +53,7 @@ asmlinkage void trace_page_fault(void);
 #define trace_alignment_check alignment_check
 #define trace_simd_coprocessor_error simd_coprocessor_error
 #define trace_async_page_fault async_page_fault
+#define trace_page_fault page_fault
 #endif
 
 dotraplinkage void do_divide_error(struct pt_regs *, long);
@@ -74,14 +74,6 @@ asmlinkage struct pt_regs *sync_regs(struct pt_regs *);
 #endif
 dotraplinkage void do_general_protection(struct pt_regs *, long);
 dotraplinkage void do_page_fault(struct pt_regs *, unsigned long);
-#ifdef CONFIG_TRACING
-dotraplinkage void trace_do_page_fault(struct pt_regs *, unsigned long);
-#else
-static inline void trace_do_page_fault(struct pt_regs *regs, unsigned long error)
-{
-	do_page_fault(regs, error);
-}
-#endif
 dotraplinkage void do_spurious_interrupt_bug(struct pt_regs *, long);
 dotraplinkage void do_coprocessor_error(struct pt_regs *, long);
 dotraplinkage void do_alignment_check(struct pt_regs *, long);
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index e5e4306e4546..9e3798b00e40 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -270,7 +270,7 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 	switch (kvm_read_and_reset_pf_reason()) {
 	default:
-		trace_do_page_fault(regs, error_code);
+		do_page_fault(regs, error_code);
 		break;
 	case KVM_PV_REASON_PAGE_NOT_PRESENT:
 		/* page is swapped out by the host. */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 955be01dd9cc..4ee9eb916826 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1253,10 +1253,6 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs)
  * This routine handles page faults.  It determines the address,
  * and the problem, and then passes it off to one of the appropriate
  * routines.
- *
- * This function must have noinline because both callers
- * {,trace_}do_page_fault() have notrace on. Having this an actual function
- * guarantees there's a function trace entry.
  */
 static noinline void
 __do_page_fault(struct pt_regs *regs, unsigned long error_code,
@@ -1491,27 +1487,6 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
 }
 NOKPROBE_SYMBOL(__do_page_fault);
 
-dotraplinkage void notrace
-do_page_fault(struct pt_regs *regs, unsigned long error_code)
-{
-	unsigned long address = read_cr2(); /* Get the faulting address */
-	enum ctx_state prev_state;
-
-	/*
-	 * We must have this function tagged with __kprobes, notrace and call
-	 * read_cr2() before calling anything else. To avoid calling any kind
-	 * of tracing machinery before we've observed the CR2 value.
-	 *
-	 * exception_{enter,exit}() contain all sorts of tracepoints.
-	 */
-
-	prev_state = exception_enter();
-	__do_page_fault(regs, error_code, address);
-	exception_exit(prev_state);
-}
-NOKPROBE_SYMBOL(do_page_fault);
-
-#ifdef CONFIG_TRACING
 static nokprobe_inline void
 trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
 			 unsigned long error_code)
@@ -1522,22 +1497,24 @@ trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
 		trace_page_fault_kernel(address, regs, error_code);
 }
 
+/*
+ * We must have this function blacklisted from kprobes, tagged with notrace
+ * and call read_cr2() before calling anything else. To avoid calling any
+ * kind of tracing machinery before we've observed the CR2 value.
+ *
+ * exception_{enter,exit}() contains all sorts of tracepoints.
+ */
 dotraplinkage void notrace
-trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
+do_page_fault(struct pt_regs *regs, unsigned long error_code)
 {
-	/*
-	 * The exception_enter and tracepoint processing could
-	 * trigger another page faults (user space callchain
-	 * reading) and destroy the original cr2 value, so read
-	 * the faulting address now.
-	 */
-	unsigned long address = read_cr2();
+	unsigned long address = read_cr2(); /* Get the faulting address */
 	enum ctx_state prev_state;
 
 	prev_state = exception_enter();
-	trace_page_fault_entries(address, regs, error_code);
+	if (trace_irqvectors_enabled())
+		trace_page_fault_entries(address, regs, error_code);
+
 	__do_page_fault(regs, error_code, address);
 	exception_exit(prev_state);
 }
-NOKPROBE_SYMBOL(trace_do_page_fault);
-#endif /* CONFIG_TRACING */
+NOKPROBE_SYMBOL(do_page_fault);
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 48ef7bb32c42..0092da1c056f 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -891,14 +891,6 @@ BUILD_INTERRUPT3(hyperv_callback_vector, HYPERVISOR_CALLBACK_VECTOR,
 
 #endif /* CONFIG_HYPERV */
 
-#ifdef CONFIG_TRACING
-ENTRY(trace_page_fault)
-	ASM_CLAC
-	pushl	$trace_do_page_fault
-	jmp	common_exception
-END(trace_page_fault)
-#endif
-
 ENTRY(page_fault)
 	ASM_CLAC
 	pushl	$do_page_fault
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ca0b250eefc4..dfabcbf8e813 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -913,17 +913,6 @@ ENTRY(\sym)
 END(\sym)
 .endm
 
-#ifdef CONFIG_TRACING
-.macro trace_idtentry sym do_sym has_error_code:req
-idtentry trace(\sym) trace(\do_sym) has_error_code=\has_error_code
-idtentry \sym \do_sym has_error_code=\has_error_code
-.endm
-#else
-.macro trace_idtentry sym do_sym has_error_code:req
-idtentry \sym \do_sym has_error_code=\has_error_code
-.endm
-#endif
-
 idtentry divide_error			do_divide_error			has_error_code=0
 idtentry overflow			do_overflow			has_error_code=0
 idtentry bounds				do_bounds			has_error_code=0
@@ -1091,7 +1080,7 @@ idtentry xen_stack_segment	do_stack_segment	has_error_code=1
 #endif
 
 idtentry general_protection	do_general_protection	has_error_code=1
-trace_idtentry page_fault	do_page_fault		has_error_code=1
+idtentry page_fault		do_page_fault		has_error_code=1
 
 #ifdef CONFIG_KVM_GUEST
 idtentry async_page_fault	do_async_page_fault	has_error_code=1
-- 
2.14.2

