Re: [PATCH v7 0/5] x86/KASLR: Add parameter kaslr_mem=nn[KMG]@ss[KMG]

From: Luiz Capitulino
Date: Thu Jan 18 2018 - 08:39:16 EST


On Thu, 18 Jan 2018 09:11:14 +0800
Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> wrote:

> 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@xxxxxxxxxxxxxx> 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.

Btw, my test tested a simple single case, but I think you can add:

Tested-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>

>
> 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(-)
> >>
> >
> >
> >
>
>