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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Thu, 11 Mar 2021 18:57:48 +0100
Message-ID: <CACT4Y+YeeEkF65O40DMLB=cggiowZUxXDs++BNTrDMO94j=NvA@mail.gmail.com>
Subject: Re: arm64 syzbot instances
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Mark Rutland <mark.rutland@arm.com>, Marc Zyngier <maz@kernel.org>,
        Will Deacon <will@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        syzkaller <syzkaller@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Mar 11, 2021 at 2:30 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > The instances found few arm64-specific issues that we have not
> > observed on other instances:
>
> I've had a brief look at these:
>
> > https://syzkaller.appspot.com/bug?id=1d22a2cc3521d5cf6b41bd6b825793c2015f861f
>
> This one  doesn't seem arm64 specific at all. While the KASAN report has shown
> up on arm64, the link to
> https://syzkaller.appspot.com/bug?id=aa8808729c0a3540e6a29f0d45394665caf79dca
> seems to be for x86 machines running into the same problem.
>
> Looking deeper into the log, I see that fw_load_sysfs_fallback() finds
> an existing
> list entry on the global "pending_fw_head" list, which seems to have been freed
> earlier (the allocation listed here is not for a firmware load, so presumably it
> was recycled in the meantime). The log shows that this is the second time that
> loading the regulatory database failed in that run, so my guess is that it was
> the first failed load that left the freed firmware private data on the
> list, but I
> don't see how that happened.
>
> > https://syzkaller.appspot.com/bug?id=bb2c16b0e13b4de4bbf22cf6a4b9b16fb0c20eea
>
> This one rings a bell: opening a 8250 uart on a well-known port must fail
> when no I/O ports are registered in the system, or when the PCI I/O ports
> are mapped to an invalid area.
>
> It seems to be attempting a register access at I/O port '1' (virtual
> address 0xfffffbfffe800001 is one byte into the well-known PCI_IOBASE),
> which is an unusual place for a UART, traditional PCs had it at 0x3F8.
>
> This could be either a result of qemu claiming to support a PIO based UART
> at the first available address, or the table of UARTS being uninitialized
> .bss memory.
>
> Definitely an arm64 specific bug.

I can reproduce this with just:

#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

int main(void)
{
  int fd = syscall(__NR_openat, 0xffffffffffffff9cul, "/dev/ttyS3", 0ul, 0ul);
  char ch = 0;
  syscall(__NR_ioctl, fd, 0x5412, &ch); // TIOCSTI
  return 0;
}


It does not even do any tty setup... does it point to a qemu bug?