linux-kernel - Re: [PATCH 22/23] userfaultfd: avoid mmap_sem read recursion in mcopy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20150522131822.74f374dd5a75a0285577c714@linux-foundation.org>
Date:	Fri, 22 May 2015 13:18:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	qemu-devel@...gnu.org, kvm@...r.kernel.org,
	linux-api@...r.kernel.org, Pavel Emelyanov <xemul@...allels.com>,
	Sanidhya Kashyap <sanidhya.gatech@...il.com>,
	zhang.zhanghailiang@...wei.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Feiner <pfeiner@...gle.com>,
	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Huangpeng (Peter)" <peter.huangpeng@...wei.com>
Subject: Re: [PATCH 22/23] userfaultfd: avoid mmap_sem read recursion in
 mcopy_atomic

On Thu, 14 May 2015 19:31:19 +0200 Andrea Arcangeli <aarcange@...hat.com> wrote:

> If the rwsem starves writers it wasn't strictly a bug but lockdep
> doesn't like it and this avoids depending on lowlevel implementation
> details of the lock.
> 
> ...
>
> @@ -229,13 +246,33 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
>  
>  		if (!zeropage)
>  			err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
> -					       dst_addr, src_addr);
> +					       dst_addr, src_addr, &page);
>  		else
>  			err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
>  						 dst_addr);
>  
>  		cond_resched();
>  
> +		if (unlikely(err == -EFAULT)) {
> +			void *page_kaddr;
> +
> +			BUILD_BUG_ON(zeropage);

I'm not sure what this is trying to do.  BUILD_BUG_ON(local_variable)?

It goes bang in my build.  I'll just delete it.

> +			up_read(&dst_mm->mmap_sem);
> +			BUG_ON(!page);
> +
> +			page_kaddr = kmap(page);
> +			err = copy_from_user(page_kaddr,
> +					     (const void __user *) src_addr,
> +					     PAGE_SIZE);
> +			kunmap(page);
> +			if (unlikely(err)) {
> +				err = -EFAULT;
> +				goto out;
> +			}
> +			goto retry;
> +		} else
> +			BUG_ON(page);
> +

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/