Messages in this thread | | | Date | Thu, 9 May 2019 07:59:15 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall |
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* Reshetova, Elena <elena.reshetova@intel.com> wrote:
> > * Reshetova, Elena <elena.reshetova@intel.com> wrote: > > > > > CONFIG_PAGE_TABLE_ISOLATION=n: > > > > > > base: Simple syscall: 0.0510 microseconds > > > get_random_bytes(4096 bytes buffer): Simple syscall: 0.0597 microseconds > > > > > > So, pure speed wise get_random_bytes() with 1 page per-cpu buffer wins. > > > > It still adds +17% overhead to the system call path, which is sad. > > Why is it so expensive? > > I guess I can experiment further with buffer size increase and/or > using HW acceleration (I mostly played around different rdrand paths now). > > What would be acceptable overheard approximately (so that I know how > much I need to squeeze this thing)?
As much as possible? No idea, I'm sad about anything that is more than 0%, and I'd be *really* sad about anything more than say 1-2%.
I find it ridiculous that even with 4K blocked get_random_bytes(), which gives us 32k bits, which with 5 bits should amortize the RNG call to something like "once per 6553 calls", we still see 17% overhead? It's either a measurement artifact, or something doesn't compute.
Thanks,
Ingo
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