linux-kernel - Re: [RFC PATCH] x86/ldt: Rename ldr_struct.size to .n

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Date:   Thu, 1 Jun 2017 19:29:45 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/ldt: Rename ldr_struct.size to .n_entries

On Wed, May 31, 2017 at 03:20:01PM -0700, Andy Lutomirski wrote:
> num_bytes, perhaps?

Better idea: entries_size.

I can read it very easily this way:

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
        struct mm_struct *mm = current->mm;
        unsigned long entries_size;
        int retval;

        mutex_lock(&mm->context.lock);

        if (!mm->context.ldt) {
                retval = 0;
                goto out_unlock;
        }

        if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
                bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;

        entries_size = mm->context.ldt->n_entries * LDT_ENTRY_SIZE;
        if (entries_size > bytecount)
                entries_size = bytecount;

        if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
                retval = -EFAULT;
                goto out_unlock;
        }

        if (entries_size != bytecount) {
                /* Zero-fill the rest and pretend we read bytecount bytes. */
                if (clear_user(ptr + entries_size, bytecount - entries_size)) {
                        retval = -EFAULT;
                        goto out_unlock;
                }
        }
        retval = bytecount;

out_unlock:
        mutex_unlock(&mm->context.lock);
        return retval;
}

> >         old_ldt = mm->context.ldt;
> > -       oldsize = old_ldt ? old_ldt->size : 0;
> > +       oldsize = old_ldt ? old_ldt->n_entries : 0;
> 
> how about old_n_entries?

Yes, and new_n_entries too:

        old_ldt       = mm->context.ldt;
        old_n_entries = old_ldt ? old_ldt->n_entries : 0;
        new_n_entries = max(ldt_info.entry_number + 1, old_n_entries);

Thanks.

-- 
Regards/Gruss,
    Boris.

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