nospec: Kill array_index_nospec_mask_check()

debian/changelog

@@ -394,6 +394,7 @@ linux (4.15.9-1) UNRELEASED; urgency=medium
     (Closes: #892629)
   * firmware_class: Refer to Debian wiki page when logging missing firmware
     (Closes: #888405)
+  * nospec: Kill array_index_nospec_mask_check()
 
   [ Uwe Kleine-König ]
   * netfilter: enable NFT_FIB_NETDEV as module

debian/patches/bugfix/all/nospec-kill-array_index_nospec_mask_check.patch

@@ -0,0 +1,77 @@
+From: Dan Williams <dan.j.williams@intel.com>
+Date: Fri, 16 Feb 2018 13:20:42 -0800
+Subject: nospec: Kill array_index_nospec_mask_check()
+Origin: https://git.kernel.org/linus/1d91c1d2c80cb70e2e553845e278b87a960c04da
+
+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 <torvalds@linux-foundation.org>
+Signed-off-by: Dan Williams <dan.j.williams@intel.com>
+Cc: Andy Lutomirski <luto@kernel.org>
+Cc: Arjan van de Ven <arjan@linux.intel.com>
+Cc: Borislav Petkov <bp@alien8.de>
+Cc: Dave Hansen <dave.hansen@linux.intel.com>
+Cc: David Woodhouse <dwmw2@infradead.org>
+Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Cc: Josh Poimboeuf <jpoimboe@redhat.com>
+Cc: Peter Zijlstra <peterz@infradead.org>
+Cc: Thomas Gleixner <tglx@linutronix.de>
+Cc: Will Deacon <will.deacon@arm.com>
+Cc: linux-arch@vger.kernel.org
+Link: http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.stgit@dwillia2-desk3.amr.corp.intel.com
+Signed-off-by: Ingo Molnar <mingo@kernel.org>
+---
+ 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));			\

debian/patches/series

@@ -120,6 +120,7 @@ features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch
 
 # Security fixes
 debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
+bugfix/all/nospec-kill-array_index_nospec_mask_check.patch
 
 # Fix exported symbol versions
 bugfix/all/module-disable-matching-missing-version-crc.patch