[syzbot] riscv/fixes test error: lost connection to test machine

[Dmitry Vyukov]

On Fri, 27 May 2022 at 14:55, syzbot
<syzbot+2c5da6a0a16a0c4f34aa at syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    c932edeaf6d6 riscv: dts: microchip: fix gpio1 reg property..
> 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=1418add5f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=aa6b5702bdf14a17
> dashboard link: https://syzkaller.appspot.com/bug?extid=2c5da6a0a16a0c4f34aa
> compiler:       riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: riscv64
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2c5da6a0a16a0c4f34aa at syzkaller.appspotmail.com

The CONFIG_KASAN_VMALLOC allows riscv kernel to boot, but now Go
processes started crashing with:

1970/01/01 00:06:55 fuzzer started
runtime: lfstack.push invalid packing: node=0xffffff5908a940 cnt=0x1
packed=0xffff5908a9400001 -> node=0xffff5908a940
fatal error: lfstack.push
runtime stack:
runtime.throw({0x30884c, 0xc})
/usr/local/go/src/runtime/panic.go:1198 +0x60
runtime.(*lfstack).push(0xdb3850, 0xffffff5908a940)
/usr/local/go/src/runtime/lfstack.go:30 +0x1a8

Go runtime tries to shove some data into the upper 16 bits of pointers
assuming they are unused.
However, the original pointer node=0xffffff5908a940 suggest riscv now
has 56-bit users-space address space?
Documentation/riscv/vm-layout.rst claims 48-bit pointers:
"
The RISC-V privileged architecture document states that the 64bit addresses
"must have bits 63–48 all equal to bit 47, or else a page-fault exception will
occur.":
...
   0000000000000000 |    0       | 0000003fffffffff |  256 GB |
user-space virtual memory, different per mm
"