[PATCH 08/13] x86: add hooks for kmemcheck

[Vegard Nossum]

The hooks that we modify are:
- Page fault handler (to handle kmemcheck faults)
- Debug exception handler (to hide pages after single-stepping
  the instruction that caused the page fault)

Also redefine memset() to use the optimized version if kmemcheck
is enabled.

(Thanks to Pekka Enberg for minimizing the impact on the page fault
 handler.)

Signed-off-by: Vegard Nossum <vegardno@xxxxxxxxxx>
---
 arch/x86/kernel/traps_32.c  |    9 +++++++++
 arch/x86/mm/fault.c         |   18 +++++++++++++++---
 include/asm-x86/string_32.h |    8 ++++++++
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index a4739a8..4ad88dd 100644
--- a/arch/x86/kernel/traps_32.c
+++ b/arch/x86/kernel/traps_32.c
@@ -57,6 +57,7 @@
 #include <asm/nmi.h>
 #include <asm/smp.h>
 #include <asm/io.h>
+#include <asm/kmemcheck.h>
 
 #include "mach_traps.h"
 
@@ -906,6 +907,14 @@ void __kprobes do_debug(struct pt_regs *regs, long error_code)
 
 	get_debugreg(condition, 6);
 
+	/* Catch kmemcheck conditions first of all! */
+	if (condition & DR_STEP) {
+		if (kmemcheck_active(regs)) {
+			kmemcheck_hide(regs);
+			return;
+		}
+	}
+
 	/*
 	 * The processor cleared BTF, so don't mark that we need it set.
 	 */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 8bcb6f4..3717195 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -33,6 +33,7 @@
 #include <asm/smp.h>
 #include <asm/tlbflush.h>
 #include <asm/proto.h>
+#include <asm/kmemcheck.h>
 #include <asm-generic/sections.h>
 
 /*
@@ -604,6 +605,13 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 	si_code = SEGV_MAPERR;
 
+	/*
+	 * Detect and handle instructions that would cause a page fault for
+	 * both a tracked kernel page and a userspace page.
+	 */
+	if(kmemcheck_active(regs))
+		kmemcheck_hide(regs);
+
 	if (notify_page_fault(regs))
 		return;
 
@@ -625,9 +633,13 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 #else
 	if (unlikely(address >= TASK_SIZE64)) {
 #endif
-		if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
-		    vmalloc_fault(address) >= 0)
-			return;
+		if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) {
+			if (vmalloc_fault(address) >= 0)
+				return;
+
+			if (kmemcheck_fault(regs, address, error_code))
+				return;
+		}
 
 		/* Can handle a stale RO->RW TLB */
 		if (spurious_fault(address, error_code))
diff --git a/include/asm-x86/string_32.h b/include/asm-x86/string_32.h
index b49369a..fade185 100644
--- a/include/asm-x86/string_32.h
+++ b/include/asm-x86/string_32.h
@@ -262,6 +262,14 @@ __asm__  __volatile__( \
  __constant_c_x_memset((s),(0x01010101UL*(unsigned char)(c)),(count)) : \
  __memset((s),(c),(count)))
 
+/* If kmemcheck is enabled, our best bet is a custom memset() that disables
+ * checking in order to save a whole lot of (unnecessary) page faults. */
+#ifdef CONFIG_KMEMCHECK
+void *kmemcheck_memset(void *s, int c, size_t n);
+#undef memset
+#define memset(s, c, n) kmemcheck_memset((s), (c), (n))
+#endif
+
 /*
  * find the first occurrence of byte 'c', or 1 past the area if none
  */
-- 
1.5.5.1

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