Re: Linux 4.9.93

From: Ard Biesheuvel
Date: Mon Apr 09 2018 - 06:25:20 EST



> On 9 Apr 2018, at 11:57, Jean-Baptiste Theou <jb@xxxxxxxxxxxxx> wrote:
>
> On Mon, 9 Apr 2018 11:49:37 +0200
> Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>
>>> On 9 April 2018 at 11:30, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>>>> On Mon, Apr 09, 2018 at 06:05:34PM +0900, Jean-Baptiste Theou wrote:
>>>> Hi,
>>>>
>>>> After this patchset, a kernel built with CFI fails. Disabling
>>>> UNMAP_KERNEL_AT_EL0 fix the issue obviously.
>>
>> How does one 'build a kernel with CFI' for arm64?
>
> From Google work on Android-4.9
>
> https://android.googlesource.com/kernel/common/+/00a195e7c0752ff5d65c9caadfbcc226270ca232
>
> I am not sure what is the plan on their side to upstream (Greg?), but definitely
> useful to isolate actual issues.
>
>>
>>>
>>> Is this a "clean" 4.9.93 tree or a "4.9.93 merged into
>>> android-common-4.9?
>
> It's a "clean 4.9.93" + whatever is needed for Clang/CFI support
>
> My take is that CFI doesn't like
>
> * void __kpti_install_ng_mappings(int cpu, int num_cpus, phys_addr_t swapper)
>
> and
>
> remap_fn = (void *)__pa_symbol(idmap_kpti_install_ng_mappings);
>
> Maybe just flag this function to not use CFI? I remember that Sami Tolvanen did
> similar changes.
>
> I know it's a bit out of context since CFI support for ARM64 is not upstream yet,
> but unfortunate that an stable patchset trigger such failures.
>

I am sorry but if you are implying that we should have tested these patches against the out of tree CFI code, I have to disappoint you: that is simply not upstreamâs job, and if the Google engineers merged this into their v4.9 tree without proper testing, may I suggest that you report it to them instead?

OTOH, if that is not what you are implying, please ignore the rant :-)


> Thanks a lot
>
> Best regards
>
>>>
>>>> Wondering if there is one of the test suite used on the review patchset that covers the CFI usecase.
>>>>
>>>> Best regards,
>>>>
>>>> [ 0.249191] CPU features: detected feature: GIC system register CPU interface
>>>> [ 0.256391] CPU features: detected feature: Privileged Access Never
>>>> [ 0.262719] CPU features: detected feature: User Access Override
>>>> [ 0.268791] CPU features: detected feature: 32-bit EL0 Support
>>>> [ 0.274683] CPU features: detected feature: Kernel page table isolation (KPTI)
>>>> [ 0.282166] CFI failure:
>>>> [ 0.282169] CFI failure:
>>>> [ 0.282172] CFI failure:
>>>> [ 0.282173] CFI failure:
>>>> [ 0.282175] CFI failure:
>>>> [ 0.282176] CFI failure:
>>>> [ 0.282177] CFI failure:
>>>> [ 0.282178] CFI failure:
>>>> [ 0.282188] ------------[ cut here ]------------
>>>> [ 0.282189] ------------[ cut here ]------------
>>>> [ 0.282190] ------------[ cut here ]------------
>>>> [ 0.282191] ------------[ cut here ]------------
>>>> [ 0.282193] ------------[ cut here ]------------
>>>> [ 0.282196] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282198] ------------[ cut here ]------------
>>>> [ 0.282201] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282202] ------------[ cut here ]------------
>>>> [ 0.282204] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282207] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282209] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282211] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282214] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282215] ------------[ cut here ]------------
>>>> [ 0.282216] kernel BUG at kernel/cfi.c:32!
>>>> [ 0.282218] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>>>> [ 0.282224] Modules linked in:
>>>> [ 0.282230] CPU: 2 PID: 25 Comm: migration/2 Not tainted 4.9.93-perf+ #39
>>>> [ 0.282232] Hardware name: <REMOVED>
>>>> [ 0.282235] task: fffffffbb3b36580 task.stack: fffffffbb30cc000
>>>> [ 0.282250] PC is at __cfi_check_fail+0x14/0x1c
>>>> [ 0.282253] LR is at __cfi_check_fail+0x14/0x1c
>>>> [ 0.282255] pc : [<ffffff93b3f03d90>] lr : [<ffffff93b3f03d90>] pstate: 60c00085
>>>> [ 0.282256] sp : fffffffbb30cfc30
>>>> [ 0.282259] x29: fffffffbb30cfc30 x28: ffffff93b6415000
>>>> [ 0.282261] x27: 00000013b65c1000 x26: ffffff93b5ce6000
>>>> [ 0.282264] x25: ffffff93b5ce6000 x24: ffffff93b6419000
>>>> [ 0.282266] x23: ffffff93b65c1000 x22: ffffff93b65c4000
>>>> [ 0.282268] x21: 9d12f8172cb2f296 x20: 000000008180e3e0
>>>> [ 0.282271] x19: 0000000000000000 x18: 000000000000002c
>>>> [ 0.282274] x17: 00000000000fd054 x16: 0000000000000000
>>>> [ 0.282276] x15: ffffff93b65ec000 x14: 000000000000000c
>>>> [ 0.282279] x13: 0000000000000004 x12: 0000000000000000
>>>> [ 0.282281] x11: 0000000000000000 x10: 0000000001440144
>>>> [ 0.282283] x9 : 260822e8751d5000 x8 : 260822e8751d5000
>>>> [ 0.282286] x7 : 0000000000000000 x6 : fffffffbbac75b60
>>>> [ 0.282288] x5 : 0000000000000000 x4 : 0000000000000000
>>>> [ 0.282290] x3 : 000000003a657275 x2 : 0000000000000000
>>>> [ 0.282292] x1 : 0000000000000000 x0 : 000000000000000c
>>>> [ 0.282294]
>>>> [ 0.282294] PC: 0xffffff93b3f03d50:
>>>> [ 0.282308] 3d50 b9001ac8 f94002c8 370ffec8 17ffffbe d4210000 14000000 aa1603e0 f90007e8
>>>> [ 0.282315] 3d70 94536017 f94007e8 17ffffe2 a9bf7bfd 910003fd d000d100 913ee400 94533cc7
>>>> [ 0.282322] 3d90 d4210000 14000000 b0013788 2a1f03e0 f901c51f d65f03c0 f940406b 2a0203e8
>>>> [ 0.282329] 3db0 2a0103e9 aa0003ea b400008b f9000145 f94000cb b40001ab a9bf7bfd 910003fd
>>>> [ 0.282330]
>>>> [ 0.282330] LR: 0xffffff93b3f03d50:
>>>> [ 0.282336] 3d50 b9001ac8 f94002c8 370ffec8 17ffffbe d4210000 14000000 aa1603e0 f90007e8
>>>> [ 0.282343] 3d70 94536017 f94007e8 17ffffe2 a9bf7bfd 910003fd d000d100 913ee400 94533cc7
>>>> [ 0.282350] 3d90 d4210000 14000000 b0013788 2a1f03e0 f901c51f d65f03c0 f940406b 2a0203e8
>>>> [ 0.282357] 3db0 2a0103e9 aa0003ea b400008b f9000145 f94000cb b40001ab a9bf7bfd 910003fd
>>>> [ 0.282358]
>>>> [ 0.282358] SP: 0xfffffffbb30cfbf0:
>>>> [ 0.282365] fbf0 b3f03d90 ffffff93 b30cfc30 fffffffb b3f03d90 ffffff93 60c00085 00000000
>>>> [ 0.282372] fc10 b6415000 ffffff93 b642fa00 ffffff93 ffffffff ffffffff b3f03d90 ffffff93
>>>> [ 0.282378] fc30 b30cfc70 fffffffb b3d458c0 ffffff93 00000080 00000000 00000001 00000000
>>>> [ 0.282385] fc50 b65c4000 ffffff93 b64420f0 ffffff93 8180e3e0 00000000 00000002 00000000
>>>> [ 0.282387] Process migration/2 (pid: 25, stack limit = 0xfffffffbb30cc000)
>>>> [ 0.282389] Call trace:
>>>> [ 0.282391] Exception stack(0xfffffffbb30cfb00 to 0xfffffffbb30cfc30)
>>>> [ 0.282395] fb00: 000000000000000c 0000000000000000 0000000000000000 000000003a657275
>>>> [ 0.282397] fb20: 0000000000000000 0000000000000000 fffffffbbac75b60 0000000000000000
>>>> [ 0.282400] fb40: 260822e8751d5000 260822e8751d5000 0000000001440144 0000000000000000
>>>> [ 0.282403] fb60: 0000000000000000 0000000000000004 000000000000000c ffffff93b65ec000
>>>> [ 0.282405] fb80: 0000000000000000 00000000000fd054 000000000000002c 0000000000000000
>>>> [ 0.282408] fba0: 000000008180e3e0 9d12f8172cb2f296 ffffff93b65c4000 ffffff93b65c1000
>>>> [ 0.282411] fbc0: ffffff93b6419000 ffffff93b5ce6000 ffffff93b5ce6000 00000013b65c1000
>>>> [ 0.282413] fbe0: ffffff93b6415000 fffffffbb30cfc30 ffffff93b3f03d90 fffffffbb30cfc30
>>>> [ 0.282416] fc00: ffffff93b3f03d90 0000000060c00085 ffffff93b6415000 ffffff93b642fa00
>>>> [ 0.282418] fc20: ffffffffffffffff ffffff93b3f03d90
>>>> [ 0.282421] [<ffffff93b3f03d90>] __cfi_check_fail+0x14/0x1c
>>>> [ 0.282430] [<ffffff93b3d458c0>] name_to_dev_t+0x0/0x47c
>>>> [ 0.282436] [<ffffff93b3d51b80>] kpti_install_ng_mappings+0x178/0x2e0
>>>> [ 0.282443] [<ffffff93b3eae950>] multi_cpu_stop+0x114/0x170
>>>> [ 0.282445] [<ffffff93b3eaf08c>] cpu_stopper_thread+0x128/0x2e8
>>>> [ 0.282452] [<ffffff93b3db5504>] smpboot_thread_fn+0x230/0x558
>>>> [ 0.282455] [<ffffff93b3dae848>] kthread+0x21c/0x238
>>>> [ 0.282459] [<ffffff93b3c838f0>] ret_from_fork+0x10/0x20
>>>> [ 0.282464] Code: 910003fd d000d100 913ee400 94533cc7 (d4210000)
>>>
>>> Oh fun :(
>>>
>>> Dragging in a bunch more people to the cc: and to: lines to have them
>>> look at this...
>>>
>>> thanks,
>>>
>>> greg k-h