Messages in this thread | | | Date | Thu, 28 Jun 2007 23:04:10 -0400 | From | Rik van Riel <> | Subject | Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer madness |
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Kyle Moffett wrote: > On Jun 28, 2007, at 14:49:24, Davide Libenzi wrote: >> I was using oprofile to sample some userspace code I am working on, >> and I was continuosly noticing clear_page in the top three entries >> of the oprofile logs. >> >> Also, a simple kernel build, in my Dual Opteron with 8GB of RAM, >> shows clear_page as the first kernel entry, second only to the >> userspace the cc1 and as. Most of the userspace code uses malloc() >> (and anonymous mappings) in such a way that the memory returned via >> kernel->glibc is immediately written soon after. The POSIX malloc() >> definition itself also, does not require the returned memory to be >> zeroed (as calloc() does). >> >> So I implemented a rather quick hack that introduces a new mmap() flag >> MAP_NOZERO (only valid for anonymous mappings) and the vma >> counter-part VM_NOZERO. Also, a new sys_brk2() has been introduced to >> accept a new flags parameter. A brief description of the patches >> follows in the next emails. > > Hmm, sounds like this would also need a "MAP_NOREUSE" flag of some kind > for security sensitive applications.
That wants MAP_PRIVATE so that the kernel can also decide to not swap these pages out to an unencrypted swap area.
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