LKML Archive on lore.kernel.org
 help / Atom feed
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Thomas Gleixner <tglx@linutronix.de>,
	Dan Williams <dan.j.williams@intel.com>,
	Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@kernel.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	stable@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] linux/nospec.h: allow index argument to have const-qualified type
Date: Thu, 15 Feb 2018 20:52:07 +0100
Message-ID: <20180215195209.15299-1-linux@rasmusvillemoes.dk> (raw)
In-Reply-To: <CAPcyv4i-bULZp1WTUgUVtdEY5i_fTGkFWKBsVLDu6dsuxUwoug@mail.gmail.com>

The last expression in a statement expression need not be a bare
variable, quoting gcc docs

  The last thing in the compound statement should be an expression
  followed by a semicolon; the value of this subexpression serves as the
  value of the entire construct.

and we already use that in e.g. the min/max macros which end with a
ternary expression.

This way, we can allow index to have const-qualified type, which will in
some cases avoid the need for introducing a local copy of index of
non-const qualified type. That, in turn, can prevent readers not
familiar with the internals of array_index_nospec from wondering about
the seemingly redundant extra variable, and I think that's worthwhile
considering how confusing the whole _nospec business is.

The expression _i&_mask has type unsigned long (since that is the type
of _mask, and the BUILD_BUG_ONs guarantee that _i will get promoted to
that), so in order not to change the type of the whole expression, add
a cast back to typeof(_i).

Cc: stable@vger.kernel.org
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
cc stable because if this is ok, there will probably be future users
relying on this which also get cc'ed to -stable.

include/linux/nospec.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/nospec.h b/include/linux/nospec.h
index fbc98e2c8228..132e3f5a2e0d 100644
--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -72,7 +72,6 @@ static inline unsigned long array_index_mask_nospec(unsigned long index,
 	BUILD_BUG_ON(sizeof(_i) > sizeof(long));			\
 	BUILD_BUG_ON(sizeof(_s) > sizeof(long));			\
 									\
-	_i &= _mask;							\
-	_i;								\
+	(typeof(_i)) (_i & _mask);					\
 })
 #endif /* _LINUX_NOSPEC_H */
-- 
2.15.1

  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-15 13:27 [PATCH] posix-timers: Protect posix clock array access against speculation Thomas Gleixner
2018-02-15 14:05 ` Rasmus Villemoes
2018-02-15 14:39   ` Dan Williams
2018-02-15 14:53     ` Thomas Gleixner
2018-02-15 16:21       ` [PATCH V2] " Thomas Gleixner
2018-02-15 17:01         ` Peter Zijlstra
2018-03-07 18:13           ` Dan Williams
2018-03-22 11:34         ` [tip:timers/urgent] " tip-bot for Thomas Gleixner
2018-02-15 19:52     ` Rasmus Villemoes [this message]
2018-02-15 20:59       ` [PATCH] linux/nospec.h: allow index argument to have const-qualified type Linus Torvalds
2018-02-15 21:56         ` Dan Williams
2018-02-15 22:03           ` Linus Torvalds
2018-02-15 22:08             ` Dan Williams

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180215195209.15299-1-linux@rasmusvillemoes.dk \
    --to=linux@rasmusvillemoes.dk \
    --cc=dan.j.williams@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=stable@vger.kernel.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --cc=will.deacon@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox