Messages in this thread | | | Date | Wed, 17 Jan 2018 12:32:35 -0500 | From | Luiz Capitulino <> | Subject | Re: [PATCH v7 0/5] x86/KASLR: Add parameter kaslr_mem=nn[KMG]@ss[KMG] |
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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.
> > 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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