Re: Option to clear allocated kernel memory before freeing it?

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On Mon, 19 Jun 2006, Michael Opdenacker wrote:

Hello,

Would it make sense to implement a kernel option that would clear kernel memory before freeing it (by kfree or free_page(s))?

Unless I'm missing something, uncleared memory previously used for kernel allocations could later be recycled for user allocations, making it possible for a user program to access sensitive driver data if it's lucky.

No sane operating system lets user-space have access to pages that haven't been cleared.

Tough clearing memory should be efficient (thanks to the use of memset(), optimized for each platform), there would of course be a significant performance hit. However, this could be acceptable for systems with strong security requirements...

A better way (and I believe the way Linux does it) is to map new pages to the zero page, read-only. If the process attempts to write to the zero page, we take a page fault and set up a new zeroed page, change the mapping, and return control back to that process.

What do you think? If this idea makes sense, I'll be glad to help in implementing it.

  Thanks in advance,

  Cheers,

  Michael.


Thanks,
Chase
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