Messages in this thread | | | Subject | Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail | From | Alex Ghiti <> | Date | Thu, 11 Mar 2021 01:39:58 -0500 |
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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.
Thanks,
Alex
> > 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 >> > >
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