Messages in this thread | | | Date | Mon, 14 Nov 2022 23:16:55 +0100 | Subject | Re: [PATCH v2 1/2] x86/stackprotector/32: Make the canary into a regular percpu variable | From | Ferry Toth <> |
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Hi
Op 14-11-2022 om 22:43 schreef Brian Gerst: > On Thu, Nov 10, 2022 at 2:36 PM Ferry Toth <fntoth@gmail.com> wrote: >> Hi, >> >> Op 09-11-2022 om 23:33 schreef Brian Gerst: >>> On Wed, Nov 9, 2022 at 9:50 AM Andy Shevchenko >>> <andriy.shevchenko@intel.com> wrote: >>>> On Fri, Sep 30, 2022 at 11:18:51PM +0200, Ferry Toth wrote: >>>>> Op 30-09-2022 om 22:30 schreef Ferry Toth: >>>>>> Op 29-09-2022 om 16:20 schreef Andy Shevchenko: >>>>>>> On Thu, Sep 29, 2022 at 04:56:07PM +0300, Andy Shevchenko wrote: >>>>>>>> On Sat, Feb 13, 2021 at 11:19:44AM -0800, Andy Lutomirski wrote: >>>>>>>>> On 32-bit kernels, the stackprotector canary is quite nasty -- it is >>>>>>>>> stored at %gs:(20), which is nasty because 32-bit kernels use %fs for >>>>>>>>> percpu storage. It's even nastier because it means that whether %gs >>>>>>>>> contains userspace state or kernel state while running kernel code >>>>>>>>> depends on whether stackprotector is enabled (this is >>>>>>>>> CONFIG_X86_32_LAZY_GS), and this setting radically changes the way >>>>>>>>> that segment selectors work. Supporting both variants is a >>>>>>>>> maintenance and testing mess. >>>>>>>>> >>>>>>>>> Merely rearranging so that percpu and the stack canary >>>>>>>>> share the same segment would be messy as the 32-bit percpu address >>>>>>>>> layout isn't currently compatible with putting a variable at a fixed >>>>>>>>> offset. >>>>>>>>> >>>>>>>>> Fortunately, GCC 8.1 added options that allow the stack canary to be >>>>>>>>> accessed as %fs:__stack_chk_guard, effectively turning it >>>>>>>>> into an ordinary >>>>>>>>> percpu variable. This lets us get rid of all of the code to >>>>>>>>> manage the >>>>>>>>> stack canary GDT descriptor and the CONFIG_X86_32_LAZY_GS mess. >>>>>>>>> >>>>>>>>> (That name is special. We could use any symbol we want for the >>>>>>>>> %fs-relative mode, but for CONFIG_SMP=n, gcc refuses to >>>>>>>>> let us use any >>>>>>>>> name other than __stack_chk_guard.) >>>>>>>>> >>>>>>>>> This patch forcibly disables stackprotector on older compilers that >>>>>>>>> don't support the new options and makes the stack canary into a >>>>>>>>> percpu variable. The "lazy GS" approach is now used for all 32-bit >>>>>>>>> configurations. >>>>>>>>> >>>>>>>>> This patch also makes load_gs_index() work on 32-bit kernels. On >>>>>>>>> 64-bit kernels, it loads the GS selector and updates the user >>>>>>>>> GSBASE accordingly. (This is unchanged.) On 32-bit kernels, >>>>>>>>> it loads the GS selector and updates GSBASE, which is now >>>>>>>>> always the user base. This means that the overall effect is >>>>>>>>> the same on 32-bit and 64-bit, which avoids some ifdeffery. >>>>>>>> This patch broke 32-bit boot on Intel Merrifield >>>>>>>> >>>>>>>> git bisect start >>>>>>>> # good: [9f4ad9e425a1d3b6a34617b8ea226d56a119a717] Linux 5.12 >>>>>>>> git bisect good 9f4ad9e425a1d3b6a34617b8ea226d56a119a717 >>>>>>>> # bad: [62fb9874f5da54fdb243003b386128037319b219] Linux 5.13 >>>>>>>> git bisect bad 62fb9874f5da54fdb243003b386128037319b219 >>>>>>>> # bad: [85f3f17b5db2dd9f8a094a0ddc665555135afd22] Merge branch >>>>>>>> 'md-fixes' of >>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/song/md into >>>>>>>> block-5.13 >>>>>>>> git bisect bad 85f3f17b5db2dd9f8a094a0ddc665555135afd22 >>>>>>>> # good: [ca62e9090d229926f43f20291bb44d67897baab7] Merge tag >>>>>>>> 'regulator-v5.13' of >>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator >>>>>>>> git bisect good ca62e9090d229926f43f20291bb44d67897baab7 >>>>>>>> # bad: [68a32ba14177d4a21c4a9a941cf1d7aea86d436f] Merge tag >>>>>>>> 'drm-next-2021-04-28' of git://anongit.freedesktop.org/drm/drm >>>>>>>> git bisect bad 68a32ba14177d4a21c4a9a941cf1d7aea86d436f >>>>>>>> # good: [49c70ece54b0d1c51bc31b2b0c1070777c992c26] >>>>>>>> drm/amd/display: Change input parameter for set_drr >>>>>>>> git bisect good 49c70ece54b0d1c51bc31b2b0c1070777c992c26 >>>>>>>> # good: [0b276e470a4d43e1365d3eb53c608a3d208cabd4] media: coda: >>>>>>>> fix macroblocks count control usage >>>>>>>> git bisect good 0b276e470a4d43e1365d3eb53c608a3d208cabd4 >>>>>>>> # bad: [c6536676c7fe3f572ba55842e59c3c71c01e7fb3] Merge tag >>>>>>>> 'x86_core_for_v5.13' of >>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip >>>>>>>> git bisect bad c6536676c7fe3f572ba55842e59c3c71c01e7fb3 >>>>>>>> # good: [d1466bc583a81830cef2399a4b8a514398351b40] Merge branch >>>>>>>> 'work.inode-type-fixes' of >>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs >>>>>>>> git bisect good d1466bc583a81830cef2399a4b8a514398351b40 >>>>>>>> # good: [fafe1e39ed213221c0bce6b0b31669334368dc97] Merge tag >>>>>>>> 'afs-netfs-lib-20210426' of >>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs >>>>>>>> git bisect good fafe1e39ed213221c0bce6b0b31669334368dc97 >>>>>>>> # bad: [b1f480bc0686e65d5413c035bd13af2ea4888784] Merge branch >>>>>>>> 'x86/cpu' into WIP.x86/core, to merge the NOP changes & resolve >>>>>>>> a semantic conflict >>>>>>>> git bisect bad b1f480bc0686e65d5413c035bd13af2ea4888784 >>>>>>>> # bad: [0c925c61dae18ee3cb93a61cc9dd9562a066034d] >>>>>>>> x86/tools/insn_decoder_test: Convert to insn_decode() >>>>>>>> git bisect bad 0c925c61dae18ee3cb93a61cc9dd9562a066034d >>>>>>>> # bad: [514ef77607b9ff184c11b88e8f100bc27f07460d] >>>>>>>> x86/boot/compressed/sev-es: Convert to insn_decode() >>>>>>>> git bisect bad 514ef77607b9ff184c11b88e8f100bc27f07460d >>>>>>>> # bad: [9e761296c52dcdb1aaa151b65bd39accb05740d9] x86/insn: >>>>>>>> Rename insn_decode() to insn_decode_from_regs() >>>>>>>> git bisect bad 9e761296c52dcdb1aaa151b65bd39accb05740d9 >>>>>>>> # bad: [d0962f2b24c99889a386f0658c71535f56358f77] x86/entry/32: >>>>>>>> Remove leftover macros after stackprotector cleanups >>>>>>>> git bisect bad d0962f2b24c99889a386f0658c71535f56358f77 >>>>>>>> # bad: [3fb0fdb3bbe7aed495109b3296b06c2409734023] >>>>>>>> x86/stackprotector/32: Make the canary into a regular percpu >>>>>>>> variable >>>>>>>> git bisect bad 3fb0fdb3bbe7aed495109b3296b06c2409734023 >>>>>>>> # first bad commit: [3fb0fdb3bbe7aed495109b3296b06c2409734023] >>>>>>>> x86/stackprotector/32: Make the canary into a regular percpu >>>>>>>> variable >>>>>> With the bad commit the last words in dmesg are: >>>>>> >>>>>> mem auto-init: stack:off, heap alloc:off, heap free:off >>>>>> Initializing HighMem for node 0 (00036ffe:0003f500) >>>>>> Initializing Movable for node 0 (00000000:00000000) >>>>>> Checking if this processor honours the WP bit even in supervisor >>>>>> mode...Ok. >>>>>> Memory: 948444K/1004124K available (12430K kernel code, 2167K rwdata, >>>>>> 4948K rodata, 716K init, 716K bss, 55680K reserved, 0K cma-reserved, >>>>>> 136200K highmem) >>>>>> SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=2, Nodes=1 >>>>>> trace event string verifier disabled >>>>>> Dynamic Preempt: voluntary >>>>>> rcu: Preemptible hierarchical RCU implementation. >>>>>> rcu: RCU event tracing is enabled. >>>>>> rcu: RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=2. >>>>>> Trampoline variant of Tasks RCU enabled. >>>>>> Tracing variant of Tasks RCU enabled. >>>>>> rcu: RCU calculated value of scheduler-enlistment delay is 100 jiffies. >>>>>> rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=2 >>>>>> NR_IRQS: 2304, nr_irqs: 512, preallocated irqs: 0 >>>>>> >>>>>> without the bad commit dmesg continues: >>>>>> >>>>>> random: get_random_bytes called from start_kernel+0x492/0x65a with >>>>>> crng_init=0 >>>>>> Console: colour dummy device 80x25 >>>>>> printk: console [tty0] enabled >>>>>> printk: bootconsole [uart0] disabled >>>>>> >>>>>> .... >>>>>> >>>>>>>> Any suggestions how to fix are welcome! >>>>>>>> >>>>> Interesting. I added the following fragment to the kernel config: >>>>> >>>>> # CONFIG_STACKPROTECTOR is not set >>>>> >>>>> And this resolves the boot issue (tested with v5.17 i686 on Intel >>>>> Merrifield) >>>> I'm not sure that's the correct approach. >> I didn't intend as a resolution, merely as a workaround. And since >> revert was not possible, as proof issue is localized in stack protector. >>>> Any answer from the Andy Lutomirski? >>>> >>>> And in general to x86 maintainers, do we support all features on x86 32-bit? If >>>> no, can it be said explicitly, please? >>> What compiler version are you using? >> I built with Yocto Honister which builds it's own cross-compiler gcc >> 11.2. For completeness: >> >> root@yuna:~# uname -a >> Linux yuna 5.17.0-edison-acpi-standard #1 SMP PREEMPT Sun Mar 20 >> 20:14:17 UTC 2022 i686 i686 i386 GNU/Linux >> >> root@yuna:~# cat /proc/version >> Linux version 5.17.0-edison-acpi-standard (oe-user@oe-host) >> (i686-poky-linux-gcc (GCC) 11.2.0, GNU ld (GNU Binutils) 2.37.20210721) >> #1 SMP PREEMPT Sun Mar 20 20:14:17 UTC 2022 >> >> root@yuna:~# cat /etc/os-release >> ID=poky-edison >> NAME="Poky (Yocto Project Reference Distro)" >> VERSION="3.4.4 (honister)" >> VERSION_ID=3.4.4 >> PRETTY_NAME="Poky (Yocto Project Reference Distro) 3.4.4 (honister)" >> >>> -- >>> Brian Gerst > What exactly happens when it fails (hang/reboot/oops)?
It just hangs. Rebooting into another kernel with CONFIG_STACKPROTECTOR not set and displaying journal of the failed boot show the last words mentioned above.
> Does removing the call to boot_init_stack_canary() in init/main.c fix > the problem? I will try tomorrow. > -- > Brian Gerst
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