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Date: Mon, 29 Jan 2018 11:05:28 +0800 From: Chao Fan <fanc.fnst@...fujitsu.com> To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>, <tglx@...utronix.de>, <mingo@...hat.com>, <bhe@...hat.com>, <keescook@...omium.org>, <yasu.isimatu@...il.com> CC: <indou.takao@...fujitsu.com>, <lcapitulino@...hat.com> Subject: Re: [PATCH v8 0/5] x86/KASLR: Add parameter kaslr_mem=nn[KMG]@ss[KMG] Hi Kees, Since no reply for one week, any suggestions for this version? Thanks, Chao Fan On Tue, Jan 23, 2018 at 04:35:41PM +0800, Chao Fan wrote: >This is v8 resend. There's no code change. Just improve code comments >and document accordingly. So add Baoquan's Acked-by and Luiz's >Tested-by. > >***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. > >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 tested this series with a 4GB KVM guest. With kaslr_mem=1G, > got one 1GB page allocated 100% of the time in 85 boots. Without > kaslr_mem=, got 3 failures in only 10 boots (that is, in 3 boots > no 1GB page allocated). So this series solves the 1GB page problem. > >***History >v7->v8: > - Just improve some comments. > - Change the wrong spelling. > - Add the Tested-by and Acked-by. > >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(-) > >-- >2.14.3 >
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