linux-kernel - Re: [PATCH] kdev_t: Always inline major/minor helper functions

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Date:   Mon, 4 Jan 2021 09:31:27 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] kdev_t: Always inline major/minor helper functions

On Mon, Jan 04, 2021 at 01:28:25PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 23, 2020 at 09:30:48AM -0600, Josh Poimboeuf wrote:
> > Silly GCC doesn't always inline these trivial functions.
> > 
> > Fixes the following warning:
> > 
> >   arch/x86/kernel/sys_ia32.o: warning: objtool: cp_stat64()+0xd8: call to new_encode_dev() with UACCESS enabled
> > 
> > Reported-by: Randy Dunlap <rdunlap@...radead.org>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> 
> The alternative is something like:

I like your approach better, it avoids __always_inline sprawl.

Peter, care to submit a proper patch?

Andrew, can you drop mine?

> 
> diff --git a/arch/x86/kernel/sys_ia32.c b/arch/x86/kernel/sys_ia32.c
> index 6cf65397d225..6ca3da08dbcb 100644
> --- a/arch/x86/kernel/sys_ia32.c
> +++ b/arch/x86/kernel/sys_ia32.c
> @@ -133,18 +133,23 @@ static int cp_stat64(struct stat64 __user *ubuf, struct kstat *stat)
>  {
>  	typeof(ubuf->st_uid) uid = 0;
>  	typeof(ubuf->st_gid) gid = 0;
> +	u64 dev, rdev;
> +
>  	SET_UID(uid, from_kuid_munged(current_user_ns(), stat->uid));
>  	SET_GID(gid, from_kgid_munged(current_user_ns(), stat->gid));
> +	dev = huge_encode_dev(stat->dev);
> +	rdev = huge_encode_dev(stat->rdev);
> +
>  	if (!user_write_access_begin(ubuf, sizeof(struct stat64)))
>  		return -EFAULT;
> -	unsafe_put_user(huge_encode_dev(stat->dev), &ubuf->st_dev, Efault);
> +	unsafe_put_user(dev, &ubuf->st_dev, Efault);
>  	unsafe_put_user(stat->ino, &ubuf->__st_ino, Efault);
>  	unsafe_put_user(stat->ino, &ubuf->st_ino, Efault);
>  	unsafe_put_user(stat->mode, &ubuf->st_mode, Efault);
>  	unsafe_put_user(stat->nlink, &ubuf->st_nlink, Efault);
>  	unsafe_put_user(uid, &ubuf->st_uid, Efault);
>  	unsafe_put_user(gid, &ubuf->st_gid, Efault);
> -	unsafe_put_user(huge_encode_dev(stat->rdev), &ubuf->st_rdev, Efault);
> +	unsafe_put_user(rdev, &ubuf->st_rdev, Efault);
>  	unsafe_put_user(stat->size, &ubuf->st_size, Efault);
>  	unsafe_put_user(stat->atime.tv_sec, &ubuf->st_atime, Efault);
>  	unsafe_put_user(stat->atime.tv_nsec, &ubuf->st_atime_nsec, Efault);
> 

-- 
Josh