[PATCH 1/3] Add prctl commands PR_GET_TSC and PR_SET_TSC

[Erik Bosman]

    This patch adds prctl commands that make it possible
    to deny the execution of timestamp counters in userspace.
    If this is not implemented on a specific architecture,
    prctl will return -EINVAL.

	Signed-off-by: Erik Bosman <ejbosman@xxxxxxxx>
---
 include/linux/prctl.h |    6 ++++++
 kernel/sys.c          |   13 ++++++++++++-
 2 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 3800639..5c80b19 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -67,4 +67,10 @@
 #define PR_CAPBSET_READ 23
 #define PR_CAPBSET_DROP 24

+/* Get/set the process' ability to use the timestamp counter instruction */
+#define PR_GET_TSC 25
+#define PR_SET_TSC 26
+# define PR_TSC_ENABLE		1	/* allow the use of the timestamp counter */
+# define PR_TSC_SIGSEGV		2	/* throw a SIGSEGV instead of reading the TSC */
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index a626116..6a0cc71 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -67,6 +67,12 @@
 #ifndef SET_ENDIAN
 # define SET_ENDIAN(a,b)	(-EINVAL)
 #endif
+#ifndef GET_TSC_CTL
+# define GET_TSC_CTL(a)		(-EINVAL)
+#endif
+#ifndef SET_TSC_CTL
+# define SET_TSC_CTL(a)		(-EINVAL)
+#endif

 /*
  * this is where the system-wide overflow UID and GID are defined, for
@@ -1737,7 +1743,12 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
 #else
 			return -EINVAL;
 #endif
-
+		case PR_GET_TSC:
+			error = GET_TSC_CTL(arg2);
+			break;
+		case PR_SET_TSC:
+			error = SET_TSC_CTL(arg2);
+			break;
 		default:
 			error = -EINVAL;
 			break;
--
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