[PATCH 4.14 115/140] nospec: Kill array_index_nospec_mask_check()

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Dan Williams 

commit 1d91c1d2c80cb70e2e553845e278b87a960c04da upstream.

There are multiple problems with the dynamic sanity checking in
array_index_nospec_mask_check():

* It causes unnecessary overhead in the 32-bit case since integer sized
  @index values will no longer cause the check to be compiled away like
  in the 64-bit case.

* In the 32-bit case it may trigger with user controllable input when
  the expectation is that should only trigger during development of new
  kernel enabling.

* The macro reuses the input parameter in multiple locations which is
  broken if someone passes an expression like 'index++' to
  array_index_nospec().

Reported-by: Linus Torvalds 
Signed-off-by: Dan Williams 
Cc: Andy Lutomirski 
Cc: Arjan van de Ven 
Cc: Borislav Petkov 
Cc: Dave Hansen 
Cc: David Woodhouse 
Cc: Greg Kroah-Hartman 
Cc: Josh Poimboeuf 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Will Deacon 
Cc: linux-a...@vger.kernel.org
Link: 
http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman 

---
 include/linux/nospec.h |   22 +-
 1 file changed, 1 insertion(+), 21 deletions(-)

--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -30,26 +30,6 @@ static inline unsigned long array_index_
 #endif
 
 /*
- * Warn developers about inappropriate array_index_nospec() usage.
- *
- * Even if the CPU speculates past the WARN_ONCE branch, the
- * sign bit of @index is taken into account when generating the
- * mask.
- *
- * This warning is compiled out when the compiler can infer that
- * @index and @size are less than LONG_MAX.
- */
-#define array_index_mask_nospec_check(index, size) 
\
-({ 
\
-   if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX,  
\
-   "array_index_nospec() limited to range of [0, LONG_MAX]\n"))
\
-   _mask = 0;  
\
-   else
\
-   _mask = array_index_mask_nospec(index, size);   
\
-   _mask;  
\
-})
-
-/*
  * array_index_nospec - sanitize an array index after a bounds check
  *
  * For a code sequence like:
@@ -67,7 +47,7 @@ static inline unsigned long array_index_
 ({ \
typeof(index) _i = (index); \
typeof(size) _s = (size);   \
-   unsigned long _mask = array_index_mask_nospec_check(_i, _s);\
+   unsigned long _mask = array_index_mask_nospec(_i, _s);  \
\
BUILD_BUG_ON(sizeof(_i) > sizeof(long));\
BUILD_BUG_ON(sizeof(_s) > sizeof(long));\

[PATCH 4.14 115/140] nospec: Kill array_index_nospec_mask_check()

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Dan Williams 

commit 1d91c1d2c80cb70e2e553845e278b87a960c04da upstream.

There are multiple problems with the dynamic sanity checking in
array_index_nospec_mask_check():

* It causes unnecessary overhead in the 32-bit case since integer sized
  @index values will no longer cause the check to be compiled away like
  in the 64-bit case.

* In the 32-bit case it may trigger with user controllable input when
  the expectation is that should only trigger during development of new
  kernel enabling.

* The macro reuses the input parameter in multiple locations which is
  broken if someone passes an expression like 'index++' to
  array_index_nospec().

Reported-by: Linus Torvalds 
Signed-off-by: Dan Williams 
Cc: Andy Lutomirski 
Cc: Arjan van de Ven 
Cc: Borislav Petkov 
Cc: Dave Hansen 
Cc: David Woodhouse 
Cc: Greg Kroah-Hartman 
Cc: Josh Poimboeuf 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Will Deacon 
Cc: linux-a...@vger.kernel.org
Link: 
http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.st...@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman 

---
 include/linux/nospec.h |   22 +-
 1 file changed, 1 insertion(+), 21 deletions(-)

--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -30,26 +30,6 @@ static inline unsigned long array_index_
 #endif
 
 /*
- * Warn developers about inappropriate array_index_nospec() usage.
- *
- * Even if the CPU speculates past the WARN_ONCE branch, the
- * sign bit of @index is taken into account when generating the
- * mask.
- *
- * This warning is compiled out when the compiler can infer that
- * @index and @size are less than LONG_MAX.
- */
-#define array_index_mask_nospec_check(index, size) 
\
-({ 
\
-   if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX,  
\
-   "array_index_nospec() limited to range of [0, LONG_MAX]\n"))
\
-   _mask = 0;  
\
-   else
\
-   _mask = array_index_mask_nospec(index, size);   
\
-   _mask;  
\
-})
-
-/*
  * array_index_nospec - sanitize an array index after a bounds check
  *
  * For a code sequence like:
@@ -67,7 +47,7 @@ static inline unsigned long array_index_
 ({ \
typeof(index) _i = (index); \
typeof(size) _s = (size);   \
-   unsigned long _mask = array_index_mask_nospec_check(_i, _s);\
+   unsigned long _mask = array_index_mask_nospec(_i, _s);  \
\
BUILD_BUG_ON(sizeof(_i) > sizeof(long));\
BUILD_BUG_ON(sizeof(_s) > sizeof(long));\