Messages in this thread | | | Date | Thu, 18 Jan 2018 09:11:14 +0800 | From | Chao Fan <> | Subject | Re: [PATCH v7 0/5] x86/KASLR: Add parameter kaslr_mem=nn[KMG]@ss[KMG] |
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On Wed, Jan 17, 2018 at 12:32:35PM -0500, Luiz Capitulino wrote: >On Wed, 17 Jan 2018 18:53:46 +0800 >Chao Fan <fanc.fnst@cn.fujitsu.com> wrote: > >> ***Background: >> People reported that kaslr may randomly chooses some positions >> which are located in movable memory regions. This will break memory >> hotplug feature. >> >> And also on kvm guest with 4GB meory, the good unfragmented 1GB could >> be occupied by randomized kernel. It will cause hugetlb failing to >> allocate 1GB page. While kernel with 'nokaslr' has not such issue. >> This causes regression. Please see the discussion mail: >> https://lkml.org/lkml/2018/1/4/236 >> >> ***Solutions: >> Introduce a new kernel parameter 'kaslr_mem=nn@ss' to let users to >> specify the memory regions where kernel can be allowed to randomize >> safely. > >I've tested this series with a 4GB KVM guest. With kaslr_mem=1G, I >got one 1GB page allocated 100% of the time in 85 boots. Without >kaslr_mem=, I got 3 failures in only 10 boots (that is, in 3 boots >I had no 1GB page allocated). > >So, this series solves the 1GB page problem for me. >
Thanks for Luiz's test.
Thanks, Chao Fan
>> >> E.g if 'movable_node' is spedified, we can use 'kaslr_mem=nn@ss' to >> tell KASLR where we can put kernel safely. Then KASLR code can avoid >> those movable regions and only choose those immovable regions >> specified. >> >> For hugetlb case, users can always add 'kaslr_mem=1G' in kernel >> cmdline since the 0~1G is always fragmented region because of BIOS >> reserved area. Surely users can specify regions more precisely if >> they know system memory very well. >> >> *** Issues need be discussed >> There are several issues I am not quite sure, please help review and >> give suggestions: >> >> 1) Since there's already mem_avoid[] which stores the memory regions >> KASLR need avoid. For the regions KASLR can safely use, I name it as >> mem_usable[], not sure if it's appropriate. Or kaslr_mem[] directly? >> >> 2) In v6, I made 'kaslr_mem=' as a kernel parameter which users can use >> to specify memory regions where kenrel can be extracted safely by >> 'kaslr_mem=nn@ss', or regions where we need avoid to extract kernel by >> 'kaslr_mem=nn!ss'. While later I rethink about it, seems >> 'kaslr_mem=nn@ss' can satisfy the current requirement, there's no need >> to introduce the 'kaslr_mem=nn!ss'. So I just take that >> 'kaslr_mem=nn!ss' handling patch off, may add it later if anyone think >> it's necessary. Any suggestions? >> https://www.spinics.net/lists/kernel/msg2698457.html >> >> ***Test results: >> - I did some tests for the memory hotplug issues. I specify the memory >> region in one node, then I found every time the kernel will be >> extracted to the memory of this node. >> - Luiz said he will do some tests for the 1G huge page issue. >> >> ***History >> v6->v7: >> - Drop the unnecessary avoid part for now. >> - Add document for the new parameter. >> >> v5->v6: >> - Add the last patch to save the avoid memory regions. >> >> v4->v5: >> - Change the problem reported by LKP >> Follow Dou's suggestion: >> - Also return if match "movable_node" when parsing kernel commandline >> in handle_mem_filter without define CONFIG_MEMORY_HOTPLUG >> >> v3->v4: >> Follow Kees's suggestion: >> - Put the functions variables of immovable_mem to #ifdef >> CONFIG_MEMORY_HOTPLUG and change some code place >> - Change the name of "process_mem_region" to "slots_count" >> - Reanme the new function "process_immovable_mem" to "process_mem_region" >> Follow Baoquan's suggestion: >> - Fail KASLR if "movable_node" specified without "immovable_mem" >> - Ajust the code place of handling mem_region directely if no >> immovable_mem specified >> Follow Randy's suggestion: >> - Change the mistake and add detailed description for the document. >> >> v2->v3: >> Follow Baoquan He's suggestion: >> - Change names of several functions. >> - Add a new parameter "immovable_mem" instead of extending mvoable_node >> - Use the clamp to calculate the memory intersecting, which makes >> logical more clear. >> - Disable memory mirror if movable_node specified >> >> v1->v2: >> Follow Dou Liyang's suggestion: >> - Add the parse for movable_node=nn[KMG] without @ss[KMG] >> - Fix the bug for more than one "movable_node=" specified >> - Drop useless variables and use mem_vector region directely >> - Add more comments. >> >> Chao Fan (5): >> x86/KASLR: Add kaslr_mem=nn[KMG]@ss[KMG] >> x86/KASLR: Handle the memory regions specified in kaslr_mem >> x86/KASLR: Give a warning if movable_node specified without kaslr_mem= >> x86/KASLR: Skip memory mirror handling if movable_node specified >> document: add document for kaslr_mem >> >> Documentation/admin-guide/kernel-parameters.txt | 10 ++ >> arch/x86/boot/compressed/kaslr.c | 154 +++++++++++++++++++++--- >> 2 files changed, 150 insertions(+), 14 deletions(-) >> > > >
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