Messages in this thread | | | Subject | Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail | From | Ben Dooks <> | Date | Thu, 11 Mar 2021 10:41:45 +0000 |
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On 11/03/2021 06:52, Dmitry Vyukov wrote: > On Thu, Mar 11, 2021 at 7:50 AM Dmitry Vyukov <dvyukov@google.com> wrote: >> >> On Thu, Mar 11, 2021 at 7:40 AM Alex Ghiti <alex@ghiti.fr> wrote: >>> >>> Hi Ben, >>> >>> Le 3/10/21 à 5:24 PM, Ben Dooks a écrit : >>>> On 10/03/2021 17:16, Dmitry Vyukov wrote: >>>>> On Wed, Mar 10, 2021 at 5:46 PM syzbot >>>>> <syzbot+e74b94fe601ab9552d69@syzkaller.appspotmail.com> wrote: >>>>>> >>>>>> Hello, >>>>>> >>>>>> syzbot found the following issue on: >>>>>> >>>>>> HEAD commit: 0d7588ab riscv: process: Fix no prototype for >>>>>> arch_dup_tas.. >>>>>> git tree: >>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1212c6e6d00000 >>>>>> kernel config: >>>>>> https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136 >>>>>> dashboard link: >>>>>> https://syzkaller.appspot.com/bug?extid=e74b94fe601ab9552d69 >>>>>> userspace arch: riscv64 >>>>>> >>>>>> Unfortunately, I don't have any reproducer for this issue yet. >>>>>> >>>>>> IMPORTANT: if you fix the issue, please add the following tag to the >>>>>> commit: >>>>>> Reported-by: syzbot+e74b94fe601ab9552d69@syzkaller.appspotmail.com >>>>> >>>>> +riscv maintainers >>>>> >>>>> This is riscv64-specific. >>>>> I've seen similar crashes in put_user in other places. It looks like >>>>> put_user crashes in the user address is not mapped/protected (?). >>>> >>>> The unmapped case should have been handled. >>>> >>>> I think this issue is that the check for user-mode access added. From >>>> what I read the code may be wrong in >>>> >>>> + if (!user_mode(regs) && addr < TASK_SIZE && >>>> + unlikely(!(regs->status & SR_SUM))) >>>> + die_kernel_fault("access to user memory without uaccess routines", >>>> + addr, regs); >>>> >>>> I think the SR_SUM check might be wrong, as I read the standard the >>>> SR_SUM should be set to disable user-space access. So the check >>>> should be unlikely(regs->status & SR_SUM) to say access without >>>> having disabled the protection. >>> >>> The check that is done seems correct to me: "The SUM (permit Supervisor >>> User Memory access) bit modifies the privilege with which S-mode loads >>> and stores access virtual memory. *When SUM=0, S-mode memory accesses >>> to pages that are accessible by U-mode (U=1 in Figure 4.15) will fault*. >>> When SUM=1, these accesses are permitted.SUM has no effect when >>> page-based virtual memory is not in effect". >>> >>> I will try to reproduce the problem locally. >> >> Weird. It crashes with this all the time: >> https://syzkaller.appspot.com/bug?extid=e74b94fe601ab9552d69 >> >> Even on trivial programs that almost don't do anything. >> Maybe it's qemu bug? Do registers look sane in the dump? That SR_SUM, etc. >> >> >> 00:13:27 executing program 1: >> openat$drirender128(0xffffffffffffff9c, >> &(0x7f0000000040)='/dev/dri/renderD128\x00', 0x0, 0x0) >> >> [ 812.318182][ T4833] Unable to handle kernel access to user memory >> without uaccess routines at virtual address 00000000250b60d0 >> [ 812.322304][ T4833] Oops [#1] >> [ 812.323196][ T4833] Modules linked in: >> [ 812.324110][ T4833] CPU: 1 PID: 4833 Comm: syz-executor.1 Not >> tainted 5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0 >> [ 812.325862][ T4833] Hardware name: riscv-virtio,qemu (DT) >> [ 812.327561][ T4833] epc : schedule_tail+0x72/0xb2 >> [ 812.328640][ T4833] ra : schedule_tail+0x70/0xb2 >> [ 812.330088][ T4833] epc : ffffffe00008c8b0 ra : ffffffe00008c8ae sp >> : ffffffe0238bbec0 >> [ 812.331312][ T4833] gp : ffffffe005d25378 tp : ffffffe00a275b00 t0 >> : 0000000000000000 >> [ 812.333014][ T4833] t1 : 0000000000000001 t2 : 00000000000f4240 s0 >> : ffffffe0238bbee0 >> [ 812.334137][ T4833] s1 : 00000000250b60d0 a0 : 0000000000000036 a1 >> : 0000000000000003 >> [ 812.336063][ T4833] a2 : 1ffffffc0cfa8b00 a3 : ffffffe0000c80cc a4 >> : 7f467e72c6adf800 >> [ 812.337398][ T4833] a5 : 0000000000000000 a6 : 0000000000f00000 a7 >> : ffffffe0000f8c84 >> [ 812.339287][ T4833] s2 : 0000000000040000 s3 : ffffffe0077a96c0 s4 >> : ffffffe020e67fe0 >> [ 812.340658][ T4833] s5 : 0000000000004020 s6 : ffffffe0077a9b58 s7 >> : ffffffe067d74850 >> [ 812.342492][ T4833] s8 : ffffffe067d73e18 s9 : 0000000000000000 >> s10: ffffffe00bd72280 >> [ 812.343668][ T4833] s11: 000000bd067bf638 t3 : 7f467e72c6adf800 t4 >> : ffffffc403ee7fb2 >> [ 812.345510][ T4833] t5 : ffffffc403ee7fba t6 : 0000000000040000 >> [ 812.347004][ T4833] status: 0000000000000120 badaddr: >> 00000000250b60d0 cause: 000000000000000f >> [ 812.348091][ T4833] Call Trace: >> [ 812.349291][ T4833] [<ffffffe00008c8b0>] schedule_tail+0x72/0xb2 >> [ 812.350796][ T4833] [<ffffffe000005570>] ret_from_exception+0x0/0x14 >> [ 812.352799][ T4833] Dumping ftrace buffer: >> [ 812.354328][ T4833] (ftrace buffer empty) >> [ 812.428145][ T4833] ---[ end trace 94b077e4d677ee73 ]--- >> >> >> 00:10:42 executing program 1: >> bpf$ENABLE_STATS(0x20, 0x0, 0x0) >> bpf$ENABLE_STATS(0x20, 0x0, 0x0) >> >> [ 646.536862][ T5163] loop0: detected capacity change from 0 to 1 >> [ 646.566730][ T5165] Unable to handle kernel access to user memory >> without uaccess routines at virtual address 00000000032f80d0 >> [ 646.586024][ T5165] Oops [#1] >> [ 646.586640][ T5165] Modules linked in: >> [ 646.587350][ T5165] CPU: 1 PID: 5165 Comm: syz-executor.1 Not >> tainted 5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0 >> [ 646.588209][ T5165] Hardware name: riscv-virtio,qemu (DT) >> [ 646.589019][ T5165] epc : schedule_tail+0x72/0xb2 >> [ 646.589811][ T5165] ra : schedule_tail+0x70/0xb2 >> [ 646.590435][ T5165] epc : ffffffe00008c8b0 ra : ffffffe00008c8ae sp >> : ffffffe008013ec0 >> [ 646.591142][ T5165] gp : ffffffe005d25378 tp : ffffffe007634440 t0 >> : 0000000000000000 >> [ 646.591836][ T5165] t1 : 0000000000000001 t2 : 0000000000000008 s0 >> : ffffffe008013ee0 >> [ 646.592509][ T5165] s1 : 00000000032f80d0 a0 : 0000000000000004 a1 >> : 0000000000000003 >> [ 646.593188][ T5165] a2 : 1ffffffc0cfac500 a3 : ffffffe0000c80cc a4 >> : 8d229faaffda9500 >> [ 646.593878][ T5165] a5 : 0000000000000000 a6 : 0000000000f00000 a7 >> : ffffffe000082eba >> [ 646.594552][ T5165] s2 : 0000000000040000 s3 : ffffffe00c82c440 s4 >> : ffffffe00e61ffe0 >> [ 646.595253][ T5165] s5 : 0000000000004000 s6 : ffffffe067d57e00 s7 >> : ffffffe067d57850 >> [ 646.595938][ T5165] s8 : ffffffe067d56e18 s9 : ffffffe067d57e00 >> s10: ffffffe00c82c878 >> [ 646.596627][ T5165] s11: 000000967ba7a1cc t3 : 8d229faaffda9500 t4 >> : ffffffc4011bc79b >> [ 646.597319][ T5165] t5 : ffffffc4011bc79d t6 : ffffffe008de3ce8 >> [ 646.597909][ T5165] status: 0000000000000120 badaddr: >> 00000000032f80d0 cause: 000000000000000f >> [ 646.598682][ T5165] Call Trace: >> [ 646.599294][ T5165] [<ffffffe00008c8b0>] schedule_tail+0x72/0xb2 >> [ 646.600115][ T5165] [<ffffffe000005570>] ret_from_exception+0x0/0x14 >> [ 646.601333][ T5165] Dumping ftrace buffer: >> [ 646.602322][ T5165] (ftrace buffer empty) >> [ 646.663691][ T5165] ---[ end trace e7b7847ce74cdfca ]--- > > Is it reasonable that schedule_tail is called from ret_from_exception? > Maybe the issue is in ret_from_exception? I see it does something with > registers.
I'd not noticed this with an earlier kernel (5.10 and the user-fault check patches) but this may be an qemu issue?
-- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius
https://www.codethink.co.uk/privacy.html
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