Messages in this thread | | | Date | Thu, 10 Nov 2022 20:36:11 +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 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
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