Does Linux process exist information leakage?

[fjohnber@zoho.com (Fredrick)]

Yes you are right.
Each architecture implements clear_page() differently. Some may just use 
memset. Some may use architecture specific instructions to perform the 
zero-ing faster.

I guess x86's fast_clear_page does that.

-Fredrick

On 01/18/2012 05:27 PM, ??? wrote:
> Thanks?
>
> It seems that the function do_page_fault() will finally call
> fast_clear_page()
> <http://lxr.oss.org.cn/plain/source/arch/x86/lib/mmx_32.c#L125> or
> slow_zero_page()
> <http://lxr.oss.org.cn/plain/source/arch/x86/lib/mmx_32.c#L336> to zero
> a new physical page for a process. So calling malloc() cannot get a page
> used by another process which is dead already.
>
> The assemble language is difficult to me, so please tell me if I am wrong.
>
> 2012/1/18 Fredrick <fjohnber at zoho.com <mailto:fjohnber@zoho.com>>
>
>     When you malloc a memory or mmap a MAP_ANON memory, it is virtually
>     allocated. When you read or write to it, the process takes a page
>     fault. The page fault handler zeroes those memory and hands it to
>     the process. So I think there is no leak.
>
>     -Fredrick
>
>
>     On 01/11/2012 04:53 AM, ??? wrote:
>
>         Hi,
>         My tutor asked me to test whether one process leaves information in
>         memory after it is dead. I tried to search some article about
>         such thing
>         on the Internet but there seems to be no one discuss about it.
>         And after
>         that, I tried to write some program in the User Mode to test it,
>         using
>         fork() to create lots of processes and filling char 'a' into a
>         102400
>         bytes char array in each process. Then I used malloc() to get some
>         memory to seek char 'a' in a new one process or many new
>         processes, but
>         failed. All memory I malloced was full of zero.
>         As the man page of malloc said:"The memory is not initialized", I
>         believe that the memory which was got by malloc() could be used
>         by other
>         process, and therefor information leakage exists. But how can I
>         test it?
>         Or where can I get related information?
>         Thanks!
>
>
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