linux-kernel - Re: [PATCH v2] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY

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Message-ID: <20160829175928.xtqneqhkq5xb5cju@treble>
Date:   Mon, 29 Aug 2016 12:59:28 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v2] mm/usercopy: get rid of
 CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

On Mon, Aug 29, 2016 at 12:08:13PM -0500, Josh Poimboeuf wrote:
> On Mon, Aug 29, 2016 at 08:36:46AM -0700, Linus Torvalds wrote:
> > On Mon, Aug 29, 2016 at 7:48 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > >
> > > So I *think* your patch fixes the wrong problem.  That's probably at
> > > least somewhat my fault because I misunderstood the issue before and may
> > > have described it wrong at some point.
> > >
> > > AFAICT, gcc isn't doing anything wrong, and the false positives are
> > > "intentional".
> > >
> > > There are in fact two static warnings (which are being silenced for new
> > > versions of gcc):
> > 
> > [ snip snip details ]
> > 
> > Ok.
> > 
> > Color me convinced, I never even looked at the two different cases, I
> > thought it was just one issue.
> > 
> > Let's just remove the spurious false positive warning then, in order
> > to re-instate the *actual* warning that right now is disabled entirely
> > due to the unrelated false positives.
> > 
> > Thanks for looking into this. Would you happen to also have a patch
> > that can be applied? Hint hint..
> 
> How about something like this?  I can split it up if needed...
> 
> ---
> 
> From: Josh Poimboeuf <jpoimboe@...hat.com>
> Subject: [PATCH v2] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

...and that failed to build on tile and parisc.  Here's the fix:

----

diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index 736c0c1..e915048 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -225,7 +225,7 @@ static inline unsigned long __must_check copy_from_user(void *to,
 
         if (likely(sz == -1 || sz >= n))
                 ret = __copy_from_user(to, from, n);
-        else (!__builtin_constant_p(n))
+        else if (!__builtin_constant_p(n))
 		copy_user_overflow(sz, n);
 	else
                 __bad_copy_user();
diff --git a/arch/tile/include/asm/uaccess.h b/arch/tile/include/asm/uaccess.h
index c664300..4416f09 100644
--- a/arch/tile/include/asm/uaccess.h
+++ b/arch/tile/include/asm/uaccess.h
@@ -433,7 +433,7 @@ static inline unsigned long __must_check copy_from_user(void *to,
 	if (likely(sz == -1 || sz >= n))
 		n = _copy_from_user(to, from, n);
 	else if (!__builtin_constant_p(n))
-		copy_user_overflow();
+		copy_user_overflow(sz, n);
 	else
 		__bad_copy_user();