linux-kernel - Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY

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Date:   Tue, 30 Aug 2016 19:12:42 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <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 v3] mm/usercopy: get rid of
 CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

On Tue, Aug 30, 2016 at 10:02:38AM -0700, Linus Torvalds wrote:
> On Tue, Aug 30, 2016 at 6:04 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > There are three usercopy warnings which are currently being silenced for
> > gcc 4.6 and newer:
> 
> [.. snip snip ..]
> 
> Ok, I'm not entirely happy with the timing, but I think the problem
> counts as a regression since it effectively made all the checks go
> away in practice for most people, so I'm going to apply this patch.
> 
> I know Al Viro is working on some uaccess cleanups and trying to make
> a lot of this be generic, so there's hopefully cleanups coming in the
> not too distant future (I say "hopefully", because I worry that
> looking at the mess will make Al dig his eyes out), but this seems to
> be a clear improvement.
> 
> I still do wish we'd move the x86 __builtin_constant_p(n) check
> around, so that x86 wouldn't do the run-time check_object_size() for
> the trivially statically correct case, but I guess that's a separate
> issue from this patch anyway.
> 
> If somebody has objections to this patch, holler quickly, because it's
> about to get applied. 3.. 2.. 1..

The only thing in my pile it conflicts with is this:

commit 0983ee6305f551faf29b11e59486679f600f1cd9
Author: Al Viro <viro@...iv.linux.org.uk>
Date:   Sat Aug 20 19:03:37 2016 -0400

    parisc: fix copy_from_user()
    
    Cc: stable@...r.kernel.org
    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index 0f59fd9..54cfea9 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -221,13 +221,14 @@ static inline unsigned long __must_check copy_from_user(void *to,
                                           unsigned long n)
 {
         int sz = __compiletime_object_size(to);
-        int ret = -EFAULT;
+        unsigned long ret = n;
 
         if (likely(sz == -1 || !__builtin_constant_p(n) || sz >= n))
                 ret = __copy_from_user(to, from, n);
         else
                 copy_from_user_overflow();
-
+	if (unlikely(ret))
+		memset(to + (n - ret), 0, ret);
         return ret;
 }