Messages in this thread | | | Subject | Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail | From | Ben Dooks <> | Date | Wed, 10 Mar 2021 22:24:30 +0000 |
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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.
Without this, you can end up with an infinite loop in the fault handler.
> >> Unable to handle kernel access to user memory without uaccess routines at virtual address 000000002749f0d0 >> Oops [#1] >> Modules linked in: >> CPU: 1 PID: 4875 Comm: syz-executor.0 Not tainted 5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0 >> Hardware name: riscv-virtio,qemu (DT) >> epc : schedule_tail+0x72/0xb2 kernel/sched/core.c:4264 >> ra : task_pid_vnr include/linux/sched.h:1421 [inline] >> ra : schedule_tail+0x70/0xb2 kernel/sched/core.c:4264 >> epc : ffffffe00008c8b0 ra : ffffffe00008c8ae sp : ffffffe025d17ec0 >> gp : ffffffe005d25378 tp : ffffffe00f0d0000 t0 : 0000000000000000 >> t1 : 0000000000000001 t2 : 00000000000f4240 s0 : ffffffe025d17ee0 >> s1 : 000000002749f0d0 a0 : 000000000000002a a1 : 0000000000000003 >> a2 : 1ffffffc0cfac500 a3 : ffffffe0000c80cc a4 : 5ae9db91c19bbe00 >> a5 : 0000000000000000 a6 : 0000000000f00000 a7 : ffffffe000082eba >> s2 : 0000000000040000 s3 : ffffffe00eef96c0 s4 : ffffffe022c77fe0 >> s5 : 0000000000004000 s6 : ffffffe067d74e00 s7 : ffffffe067d74850 >> s8 : ffffffe067d73e18 s9 : ffffffe067d74e00 s10: ffffffe00eef96e8 >> s11: 000000ae6cdf8368 t3 : 5ae9db91c19bbe00 t4 : ffffffc4043cafb2 >> t5 : ffffffc4043cafba t6 : 0000000000040000 >> status: 0000000000000120 badaddr: 000000002749f0d0 cause: 000000000000000f >> Call Trace: >> [<ffffffe00008c8b0>] schedule_tail+0x72/0xb2 kernel/sched/core.c:4264 >> [<ffffffe000005570>] ret_from_exception+0x0/0x14 >> Dumping ftrace buffer: >> (ftrace buffer empty) >> ---[ end trace b5f8f9231dc87dda ]--- >> >> >> --- >> This report is generated by a bot. It may contain errors. >> See https://goo.gl/tpsmEJ for more information about syzbot. >> syzbot engineers can be reached at syzkaller@googlegroups.com. >> >> syzbot will keep track of this issue. See: >> https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >> >> -- >> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. >> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. >> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/000000000000b74f1b05bd316729%40google.com. > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv >
-- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius
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