Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] mm/uaccess: Use 'unsigned long' to placate UBSAN
 warnings, again
To:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Cc:     linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>
References: <590998aa9cc50f431343f76cae72b2abf8ac1fdd.1608699683.git.jpoimboe@redhat.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <6823854f-019f-f9db-7fd8-da8e7a0016d1@infradead.org>
Date:   Tue, 22 Dec 2020 23:18:56 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.4.0
MIME-Version: 1.0
In-Reply-To: <590998aa9cc50f431343f76cae72b2abf8ac1fdd.1608699683.git.jpoimboe@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 12/22/20 9:04 PM, Josh Poimboeuf wrote:
> GCC 7 has a known bug where UBSAN ignores '-fwrapv' and generates false
> signed-overflow-UB warnings.  The type mismatch between 'i' and
> 'nr_segs' in copy_compat_iovec_from_user() is causing such a warning,
> which also happens to violate uaccess rules:
> 
>   lib/iov_iter.o: warning: objtool: iovec_from_user()+0x22d: call to __ubsan_handle_add_overflow() with UACCESS enabled
> 
> Fix it by making the variable types match.
> 
> This is similar to a previous commit:
> 
>   29da93fea3ea ("mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions")
> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

All good. Thanks.

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested


> ---
>  lib/iov_iter.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 1635111c5bd2..2e6a42f5d1df 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1656,7 +1656,8 @@ static int copy_compat_iovec_from_user(struct iovec *iov,
>  {
>  	const struct compat_iovec __user *uiov =
>  		(const struct compat_iovec __user *)uvec;
> -	int ret = -EFAULT, i;
> +	int ret = -EFAULT;
> +	unsigned long i;
>  
>  	if (!user_access_begin(uvec, nr_segs * sizeof(*uvec)))
>  		return -EFAULT;
> 


-- 
~Randy