[PATCH] Define vsyscall cache as blob to make clearer that user space shouldn't use it

Signed-off-by: Andi Kleen <ak@suse.de>

3 files changed, 15 insertions, 13 deletions

diff --git a/arch/x86_64/kernel/vsyscall.c b/arch/x86_64/kernel/vsyscall.c
index ac48c3857ddb..07c086382059 100644
--- a/arch/x86_64/kernel/vsyscall.c
+++ b/arch/x86_64/kernel/vsyscall.c
@@ -155,8 +155,8 @@ vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
            We do this here because otherwise user space would do it on
            its own in a likely inferior way (no access to jiffies).
            If you don't like it pass NULL. */
-        if (tcache && tcache->t0 == (j = __jiffies)) {
-                p = tcache->t1;
+        if (tcache && tcache->blob[0] == (j = __jiffies)) {
+                p = tcache->blob[1];
         } else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
                 /* Load per CPU data from RDTSCP */
                 rdtscp(dummy, dummy, p);
@@ -165,8 +165,8 @@ vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
                 asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
         }
         if (tcache) {
-                tcache->t0 = j;
-                tcache->t1 = p;
+                tcache->blob[0] = j;
+                tcache->blob[1] = p;
         }
         if (cpu)
                 *cpu = p & 0xfff;
diff --git a/include/linux/getcpu.h b/include/linux/getcpu.h
index 031ed3780e45..c7372d7a97be 100644
--- a/include/linux/getcpu.h
+++ b/include/linux/getcpu.h
@@ -1,16 +1,18 @@
 #ifndef _LINUX_GETCPU_H
 #define _LINUX_GETCPU_H 1
 
-/* Cache for getcpu() to speed it up. Results might be upto a jiffie
+/* Cache for getcpu() to speed it up. Results might be a short time
    out of date, but will be faster.
+
    User programs should not refer to the contents of this structure.
-   It is only a cache for vgetcpu(). It might change in future kernels.
+   I repeat they should not refer to it. If they do they will break
+   in future kernels.
+
+   It is only a private cache for vgetcpu(). It will change in future kernels.
    The user program must store this information per thread (__thread)
    If you want 100% accurate information pass NULL instead. */
 struct getcpu_cache {
-        unsigned long t0;
-        unsigned long t1;
-        unsigned long res[4];
+        unsigned long blob[128 / sizeof(long)];
 };
 
 #endif
diff --git a/kernel/sys.c b/kernel/sys.c
index 8647061c084a..b88806c66244 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2083,12 +2083,12 @@ asmlinkage long sys_getcpu(unsigned __user *cpup, unsigned __user *nodep,
                  * padding
                  */
                 unsigned long t0, t1;
-                get_user(t0, &cache->t0);
-                get_user(t1, &cache->t1);
+                get_user(t0, &cache->blob[0]);
+                get_user(t1, &cache->blob[1]);
                 t0++;
                 t1++;
-                put_user(t0, &cache->t0);
-                put_user(t1, &cache->t1);
+                put_user(t0, &cache->blob[0]);
+                put_user(t1, &cache->blob[1]);
         }
         return err ? -EFAULT : 0;
 }