September 2020 - kernelnewbies@kernelnewbies.org

Re: KASLR support on ARM with Kernel 4.9 and 4.14
by Kees Cook Sept. 25, 2020

Sept. 25, 2020

On Fri, Sep 25, 2020 at 10:37:01PM +0200, Ard Biesheuvel wrote: > On Fri, 25 Sep 2020 at 22:28, Kees Cook <keescook(a)chromium.org> wrote: > > > > On Fri, Sep 25, 2020 at 08:33:59PM +0530, Pintu Agarwal wrote: > > > This is regarding the KASLR feature support on ARM for the kernel > > > version 4.9 and 4.14. > > > > > > Is KASLR supported on ARM-32 Linux 4.9 and above ? > > > > Sorry, this feature did not yet land in upstream: > > https://github.com/KSPP/linux/issues/3 > > > > Here was the earlier effort: > > https://lore.kernel.org/kernel-hardening/20170814125411.22604-1-ard.biesheu… > > > > > Is it dependent on CONFIG_RANDOMIZE_BASE or > > > > CONFIG_RANDOMIZE_BASE is what is used on other architectures to control > > the feature. > > > > > /proc/sys/kernel/randomize_va_space ? > > > Is there any relation between these two? > > > > No, the latter is about userspace addresses. > > > > > Is the changing kernel symbols (in every boot), only possible if KASLR > > > is enabled, or there is another way it can happen? > > > > I think you meant kernel symbol addresses (not the symbols themselves). > > But yes, I wouldn't expect the addresses to move if you didn't either > > rebuild the kernel or had something else moving the kernel at boot (i.e. > > the boot loader). > > > > > I have these queries because, > > > In one of the arm-32 devices with Kernel 4.14, I observed that > > > CONFIG_RANDOMIZE_BASE is not available. > > > But /proc/sys/kernel/randomize_va_space is set to 2. > > > However, I also observed that symbol addresses are changing in every boot. > > > > > > 1st boot cycle: > > > [root ~]# cat /proc/kallsyms | grep "sys_open" > > > a5b4de92 T sys_open > > > [root@sa515m ~]# > > > > > > 2nd boot cycle: > > > [root ~]# cat /proc/kallsyms | grep "sys_open" > > > f546ed66 T sys_open > > > > > > So, I am wondering how this is possible without KASLR > > > (CONFIG_RANDOMIZE_BASE) support in Kernel ? > > Those addresses were obfuscated by kptr_restrict Is that true? kptr_restrict zeros (rather than hashing) the kallsyms view. And besides, the %p hashing was added in v4.15 (but also doesn't touch kallsyms, which does all-or-nothing to avoid breaking stuff like perf). -- Kees Cook

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KASLR support on ARM with Kernel 4.9 and 4.14
by Pintu Agarwal Sept. 25, 2020

Sept. 25, 2020

Hi All, This is regarding the KASLR feature support on ARM for the kernel version 4.9 and 4.14. Is KASLR supported on ARM-32 Linux 4.9 and above ? Is it dependent on CONFIG_RANDOMIZE_BASE or /proc/sys/kernel/randomize_va_space ? Is there any relation between these two? Is the changing kernel symbols (in every boot), only possible if KASLR is enabled, or there is another way it can happen? I have these queries because, In one of the arm-32 devices with Kernel 4.14, I observed that CONFIG_RANDOMIZE_BASE is not available. But /proc/sys/kernel/randomize_va_space is set to 2. However, I also observed that symbol addresses are changing in every boot. 1st boot cycle: [root ~]# cat /proc/kallsyms | grep "sys_open" a5b4de92 T sys_open [root@sa515m ~]# 2nd boot cycle: [root ~]# cat /proc/kallsyms | grep "sys_open" f546ed66 T sys_open So, I am wondering how this is possible without KASLR (CONFIG_RANDOMIZE_BASE) support in Kernel ? Similarly, with Kernel 4.9 and CONFIG_RANDOMIZE_BASE is not available but /proc/sys/kernel/randomize_va_space is set to 2. But here, the addresses are remaining same. 1st Run: [root~]# cat /proc/kallsyms | grep "sys_open" c01ed68c T sys_open [root ~]# *** reboot *** [root ~]# cat /proc/kallsyms | grep "sys_open" c01ed68c T sys_open Is there any other difference between these two kernel versions with respect to changing symbol addresses ? Thanks, Pintu

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Re: [Cocci] coccinelle: Convert comma to semicolons (was Re: [PATCH] checkpatch: Add test for comma use that should be semicolon)
by Joe Perches Sept. 24, 2020

Sept. 24, 2020

On Thu, 2020-09-24 at 22:19 +0200, Thomas Gleixner wrote: > On Sat, Aug 22 2020 at 09:07, Julia Lawall wrote: > > On Fri, 21 Aug 2020, Joe Perches wrote: > > > True enough for a general statement, though the coccinelle > > > script Julia provided does not change a single instance of > > > for loop expressions with commas. > > > > > > As far as I can tell, no logic defect is introduced by the > > > script at all. > > > > The script has a rule to ensure that what is changed is part of a top > > level statement that has the form e1, e2;. I put that in to avoid > > transforming cases where the comma is the body of a macro, but it protects > > against for loop headers as well. > > Right. I went through the lot and did not find something dodgy. Except > for two hunks this still applies. Can someone please send a proper patch > with changelog/SOB etc. for this? Treewide? Somebody no doubt would complain, but there _really should_ be some mechanism for these trivial and correct treewide changes...

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Re: [Cocci] coccinelle: Convert comma to semicolons (was Re: [PATCH] checkpatch: Add test for comma use that should be semicolon)
by Julia Lawall Sept. 24, 2020

Sept. 24, 2020

On Thu, 24 Sep 2020, Thomas Gleixner wrote: > On Sat, Aug 22 2020 at 09:07, Julia Lawall wrote: > > On Fri, 21 Aug 2020, Joe Perches wrote: > >> True enough for a general statement, though the coccinelle > >> script Julia provided does not change a single instance of > >> for loop expressions with commas. > >> > >> As far as I can tell, no logic defect is introduced by the > >> script at all. > > > > The script has a rule to ensure that what is changed is part of a top > > level statement that has the form e1, e2;. I put that in to avoid > > transforming cases where the comma is the body of a macro, but it protects > > against for loop headers as well. > > Right. I went through the lot and did not find something dodgy. Except > for two hunks this still applies. Can someone please send a proper patch > with changelog/SOB etc. for this? > > And of course that script really wants to be part of the kernel cocci > checks to catch further instances. I will try to get to it soon. Thanks for checking all the cases. julia > > Thanks, > > tglx >

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Re: [Cocci] coccinelle: Convert comma to semicolons (was Re: [PATCH] checkpatch: Add test for comma use that should be semicolon)
by Joe Perches Sept. 24, 2020

Sept. 24, 2020

(forwarding on to kernel-janitors/mentees and kernelnewbies) Just fyi for anyone that cares: A janitorial task for someone might be to use Julia's coccinelle script below to convert the existing instances of commas that separate statements into semicolons. https://lore.kernel.org/lkml/alpine.DEB.2.22.394.2008201856110.2524@hadrien/ On Thu, 2020-08-20 at 19:03 +0200, Julia Lawall wrote: > > > I have a bunch of variations of this that are more complicated than I > > > would have expected. One shorter variant that I have is: > > > > > > @@ > > > expression e1,e2; > > > statement S; > > > @@ > > > > > > S > > > e1 > > > -, > > > +; > > > (<+... e2 ...+>); > > > > > > This will miss cases where the first statement is the comma thing. But I > > > think it is possible to improve this now. I will check. > > > > Hi Julia. > > > > Right, thanks, this adds a dependency on a statement > > before the expression. Any stragglers would be easily > > found using slightly different form. > > There are not very many of these in linux kernel. > > > > Another nicety would be to allow the s/,/;/ conversion to > > find both b and c in this sequence: > > a = 1; > > b = 2, > > c = 3, > > d = 4; > > without running the script multiple times. > > There are many dozen uses of this style in linux kernel. > > > > I tried variants of adding a comma after the e2 expression, > > but cocci seems to have parsing problems with: > > > > @@ > > expression e1; > > expression e2; > > @@ > > e1 > > - , > > + ; > > e2, > > This doesn't work because it's not a valid expression. > > The problem is solved by doing: > > e1 > - , > + ; > e2 > ... when any > > But that doesn't work in the current version of Coccinelle. I have fixed > the problem, though and it will work shortly. > > > I do appreciate that coccinelle adds braces for multiple > > expression comma use after an if. > > > > i.e.: > > if (foo) > > a = 1, b = 2; > > becomes > > if (foo) { > > a = 1; b = 2; > > } > > I wasn't sure what was wanted for such things. Should b = 2 now be on a > separate line? > > I took the strategy of avoiding the problem and leaving those cases as is. > That also solves the LIST_HEAD problem. But if it is wanted to change > these commas under ifs, then that is probably possible too. > > My current complete solution is as follows. The first rule avoids changing > commas in macros, where thebody of the macro is just an expression. The > second rule uses position variables to ensure that the two expression are > on different lines. > > @r@ > expression e1,e2; > statement S; > position p; > @@ > > e1 ,@S@p e2; > > @@ > expression e1,e2; > position p1; > position p2 : > script:ocaml(p1) { not((List.hd p1).line_end = (List.hd p2).line) }; > statement S; > position r.p; > @@ > > e1@p1 > -,@S@p > +; > e2@p2 > ... when any > > The generated patch is below. > > julia > > diff -u -p a/drivers/reset/hisilicon/reset-hi3660.c b/drivers/reset/hisilicon/reset-hi3660.c > --- a/drivers/reset/hisilicon/reset-hi3660.c > +++ b/drivers/reset/hisilicon/reset-hi3660.c > @@ -89,7 +89,7 @@ static int hi3660_reset_probe(struct pla > return PTR_ERR(rc->map); > } > > - rc->rst.ops = &hi3660_reset_ops, > + rc->rst.ops = &hi3660_reset_ops; > rc->rst.of_node = np; > rc->rst.of_reset_n_cells = 2; > rc->rst.of_xlate = hi3660_reset_xlate; The rest of the changes are in the link above...

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Using FPGA subsystem to upload bit-stream using altera-ps-spi.
by Grzegorz Heldt Sept. 24, 2020

Sept. 24, 2020

Hello. I'm looking for suggestion of correct way of FPGA programming in my system. This is an am335x based board, yocto based with kernel 4.19. It has FPGA connected through "altera passive serial". There exists a specific kernel module especially made for such scenario, and I was able to include its configuration in device-tree. >From what I was able to find, there are three ways of programming FPGA using FPGA subsystem. 1. I should be able to see /sys/class/fpga_manager/fpga0/firmware or /sys/class/fpga_manager/fpga0/fpga files, which I can use to upload bitstream to fpga. The problem is that I can't see those files. Both altera-ps-spi and fpga-manager drivers do not report any errors, but the result is that I can see some files /sys/class/fpga_manager/fpga0, but no "firmware" or "fpga" files exist. "cat state" result is "unknown". At this point I have no idea how to go further. 2. I can use DT overlays that can disable device drivers already provided by FPGA, do programming, and rediscover drivers provided by FPGA. At the moment I don't see the need for such features in this system, but the approach looks sexy. In my system I can see configfs mounted at /sys/kernel/config. However, based on information that I was able to find, I should see or create /sys/kernel/config/device-tree/ directory. I can't see it and I can't create. Runtime DT overlays look extremely sexy to me, I have played with them on RPI. Very sad I don't know how to enable them on my system. 3. Using kernel API. I haven't tried yet, as I rather like to use methods that will required less possible maintenance in future. Can some suggest: - which of these three methods is most proper ? - how to go forward with way 1 or 2 ? Best Regards Greg.

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Compiled Kernel stuck in booting
by Yashodhan Joshi Sept. 23, 2020

Sept. 23, 2020

Hello, I use a dual boot laptop with windows and Ubuntu,with grub2. I Followed the instruction in https://kernelnewbies.org/OutreachyfirstpatchSetup to clone the source code and compile the kernel, which was done without any errors. When I tried to install the kernel using 'sudo make modules_install install' it showed a warning when updating initramfs, that it will attempt to resume from UUID, which is my SWAP space, but other than that it showed no other errors. When I tried to boot into it from the grub menu after restarting, it showed message of loading the kernel and then 'setting up intitial ramdisk', after which nothing further happend. The default kernel that came with ubuntu is still working and boots up into desktop environment withing 2-3 minutes after the 'ramdisk' message, but even though I kept the system running for 20 minutes after the 'ramdisk' message for the compiled kernel, niether any further proccess seems to be happening nor any error messages are shown. Can someone help me figuring out what is wrong and how can I run the kernel? Thank You. Also can someone point me in right direction to send suggestions about updating the information on kernelnewbies website? The information about connecting mutt to Gmail is quite outdated, and I would like to help updating it.

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memory mapping from user space to kernel space
by JeongHwan Kim Sept. 19, 2020

Sept. 19, 2020

Hi, everyone The memory mapping from memory allocated in kernel space to user space is possible to use mmap, but is it possible to map memory allocated in user space to kernel? Thanks in advance J.H.Kim

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Not able to find reference text for the latest linux kernel process scheduler
by Rohit Chourasia Sept. 15, 2020

Sept. 15, 2020

Hi, I have just begun studying the linux process scheduling and I find that most of the textsbooks are quiet outdated and the latest kernel codes do not match the text. How should I proceed further ? Thanks and Regards, Rohit Chourasia

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Can't understand VM_PFNMAP and VM_MIXEDMAP flag
by Hao Lee Sept. 14, 2020

Sept. 14, 2020

Hi, I'm confused by VM_PFNMAP and VM_MIXEDMAP flag. Could someone explain what these two flags mean and why we need them? It would be better to give some examples. Thanks! Thanks, Hao Lee

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