Messages in this thread Patch in this message | | | Date | Thu, 5 Jan 2017 21:52:43 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v3 1/3] x86/64: Make kernel text mapping always take one whole page table in early boot code |
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On Thu, Jan 05, 2017 at 11:35:57AM -0800, Kees Cook wrote: > The only reason I had it as an option was for kernel module space. It > wasn't clear to me at the time if enough space remained for modules in > all use-cases. It seems like probably there is, so I have no objection > to making the mapping 1G unconditionally.
Oh someone will crawl out of the woodwork handwaiving that 1G of modules is not enough. But then that someone would have to choose between kaslr and >1G modules.
Realistically, on a typical bigger machine, the modules take up something like <10M:
$ lsmod | awk '{ sum +=$2 } END { print sum }' 7188480
so I'm not really worried if we reduce it by default to 1G. Besides, the reduction has been there for a while now - since CONFIG_RANDOMIZE_BASE - so we probably would've heard complaints already...
Btw, we should probably document the reduction in the va map document too:
--- From: Borislav Petkov <bp@suse.de> Date: Thu, 5 Jan 2017 21:47:18 +0100 Subject: [PATCH] x86/mm: Document modules space reduction
KASLR reduces module mapping space to 1G, document that.
Signed-off-by: Borislav Petkov <bp@suse.de> --- Documentation/x86/x86_64/mm.txt | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt index 5724092db811..a737dfbc198b 100644 --- a/Documentation/x86/x86_64/mm.txt +++ b/Documentation/x86/x86_64/mm.txt @@ -39,6 +39,8 @@ memory window (this size is arbitrary, it can be raised later if needed). The mappings are not part of any other kernel PGD and are only available during EFI runtime calls. +CONFIG_RANDOMIZE_BASE (KASLR) reduces module mapping space from 1.5G to 1G. + Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all physical memory, vmalloc/ioremap space and virtual memory map are randomized. Their order is preserved but their base will be offset early at boot time. -- 2.11.0 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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