x86: add hooks for kmemcheck

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.)

As kmemcheck doesn't handle MMX/SSE instructions (yet), we also disable
the optimized xor code, and rely instead on the generic C implementation
in order to avoid false-positive warnings.

Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>

[whitespace fixlet]
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>

2 files changed, 28 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index daed39ba2614..3260ab044996 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -86,6 +86,29 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
          */
         if (c->x86 == 6 && c->x86_model < 15)
                 clear_cpu_cap(c, X86_FEATURE_PAT);
+
+#ifdef CONFIG_KMEMCHECK
+        /*
+         * P4s have a "fast strings" feature which causes single-
+         * stepping REP instructions to only generate a #DB on
+         * cache-line boundaries.
+         *
+         * Ingo Molnar reported a Pentium D (model 6) and a Xeon
+         * (model 2) with the same problem.
+         */
+        if (c->x86 == 15) {
+                u64 misc_enable;
+
+                rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+
+                if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
+                        printk(KERN_INFO "kmemcheck: Disabling fast string operations\n");
+
+                        misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING;
+                        wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+                }
+        }
+#endif
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 07d60c870ce2..e7a28e6aa4bc 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -45,6 +45,7 @@
 #include <linux/edac.h>
 #endif
 
+#include <asm/kmemcheck.h>
 #include <asm/stacktrace.h>
 #include <asm/processor.h>
 #include <asm/debugreg.h>
@@ -534,6 +535,10 @@ dotraplinkage 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 && kmemcheck_trap(regs))
+                return;
+
         /*
          * The processor cleared BTF, so don't mark that we need it set.
          */