Messages in this thread | | | From | Brian Gerst <> | Date | Wed, 9 Nov 2022 17:33:24 -0500 | Subject | Re: [PATCH v2 1/2] x86/stackprotector/32: Make the canary into a regular percpu variable |
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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. > 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?
-- Brian Gerst
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