linux-kernel - Re: [PATCH] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings, again

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Date:   Tue, 22 Dec 2020 23:18:56 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm/uaccess: Use 'unsigned long' to placate UBSAN
 warnings, again

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@...radead.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

All good. Thanks.

Acked-by: Randy Dunlap <rdunlap@...radead.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