This is a note to let you know that I've just added the patch titled
nospec: Kill array_index_nospec_mask_check()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nospec-kill-array_index_nospec_mask_check.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1d91c1d2c80cb70e2e553845e278b87a960c04da Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Fri, 16 Feb 2018 13:20:42 -0800
Subject: nospec: Kill array_index_nospec_mask_check()
From: Dan Williams <dan.j.williams@xxxxxxxxx>
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 <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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)); \
Patches currently in stable-queue which might be from dan.j.williams@xxxxxxxxx are
queue-4.9/nospec-include-asm-barrier.h-dependency.patch
queue-4.9/x86-speculation-objtool-annotate-indirect-calls-jumps-for-objtool.patch
queue-4.9/nospec-kill-array_index_nospec_mask_check.patch