linux-kernel - Re: [PATCH v7 3.2-rc2 5/30] uprobes: copy of the original instruction.

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Date:	Mon, 28 Nov 2011 15:23:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Wilson <wilsons@...rt.ca>
Subject: Re: [PATCH v7 3.2-rc2 5/30] uprobes: copy of the original
 instruction.

On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote:
> +static int __copy_insn(struct address_space *mapping,
> +                       struct vm_area_struct *vma, char *insn,
> +                       unsigned long nbytes, unsigned long offset)
> +{
> +       struct file *filp = vma->vm_file;
> +       struct page *page;
> +       void *vaddr;
> +       unsigned long off1;
> +       unsigned long idx;
> +
> +       if (!filp)
> +               return -EINVAL;
> +
> +       idx = (unsigned long)(offset >> PAGE_CACHE_SHIFT);
> +       off1 = offset &= ~PAGE_MASK;
> +
> +       /*
> +        * Ensure that the page that has the original instruction is
> +        * populated and in page-cache.
> +        */
> +       page = read_mapping_page(mapping, idx, filp);
> +       if (IS_ERR(page))
> +               return -ENOMEM;
> +
> +       vaddr = kmap_atomic(page);
> +       memcpy(insn, vaddr + off1, nbytes);
> +       kunmap_atomic(vaddr);
> +       page_cache_release(page);
> +       return 0;
> +}
> +
> +static int copy_insn(struct uprobe *uprobe, struct vm_area_struct *vma,
> +                                       unsigned long addr)
> +{
> +       struct address_space *mapping;
> +       int bytes;
> +       unsigned long nbytes;
> +
> +       addr &= ~PAGE_MASK;
> +       nbytes = PAGE_SIZE - addr;
> +       mapping = uprobe->inode->i_mapping;
> +
> +       /* Instruction at end of binary; copy only available bytes */
> +       if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
> +               bytes = uprobe->inode->i_size - uprobe->offset;
> +       else
> +               bytes = MAX_UINSN_BYTES;
> +
> +       /* Instruction at the page-boundary; copy bytes in second page */
> +       if (nbytes < bytes) {
> +               if (__copy_insn(mapping, vma, uprobe->insn + nbytes,
> +                               bytes - nbytes, uprobe->offset + nbytes))
> +                       return -ENOMEM;

You just lost your possible -EINVAL return value.

> +
> +               bytes = nbytes;
> +       }
> +       return __copy_insn(mapping, vma, uprobe->insn, bytes, uprobe->offset);
> +} 
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