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Message-ID: <CAO6TR8V_0svJ8VsUX-m3pBWheR=yVkpLvmEk5+MD+2okcN9Y+Q@mail.gmail.com>
Date: Fri, 8 Jan 2016 14:10:49 -0700
From: Jeff Merkey <linux.mdb@...il.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Gleb Natapov <gleb@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
"x86@...nel.org" <x86@...nel.org>, kvm@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>,
syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: kvm: GPF in native_set_debugreg
On 1/8/16, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> Hello,
>
> The following program triggers GPF in native_set_debugreg if run in
> a parallel loop:
>
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <unistd.h>
> #include <sys/syscall.h>
> #include <string.h>
> #include <stdint.h>
> #include <pthread.h>
>
> long r[8];
>
> void *thr(void *arg)
> {
> switch ((long)arg) {
> case 0:
> r[0] = syscall(SYS_mmap, 0x20000000ul, 0x7000ul,
> 0x3ul, 0x32ul, 0xfffffffffffffffful, 0x0ul);
> break;
> case 1:
> memcpy((void*)0x200008ab,
> "\x2f\x64\x65\x76\x2f\x6b\x76\x6d", 8);
> r[2] = syscall(SYS_open, 0x200008abul, 0x0ul, 0x0ul, 0, 0,
> 0);
> break;
> case 2:
> r[3] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0);
> break;
> case 3:
> r[4] = syscall(SYS_ioctl, r[3], 0xae41ul, 0x7ul, 0, 0, 0);
> break;
> case 4:
> r[5] = syscall(SYS_ioctl, r[4], 0xae80ul, 0, 0, 0, 0);
> break;
> case 5:
> memcpy((void*)0x20001000,
> "\x5d\x6a\x6b\xe8\x57\x3b\x4b\x7e\xcf\x0d\xa1\x72\xa3\x4a\x29\x0c\xfc\x6d\x44\x00\xa7\x52\xc7\xd8\x00\xdb\x89\x9d\x78\xb5\x54\x6b\x6b\x13\x1c\xe9\x5e\xd3\x0e\x40\x6f\xb4\x66\xf7\x5b\xe3\x36\xcb",
> 48);
> r[7] = syscall(SYS_ioctl, r[4], 0x4080aea2ul,
> 0x20001000ul, 0, 0, 0);
> break;
> }
> return 0;
> }
>
> int main()
> {
> long i;
> pthread_t th[6];
>
> memset(r, -1, sizeof(r));
> for (i = 0; i < 6; i++) {
> pthread_create(&th[i], 0, thr, (void*)i);
> usleep(10000);
> }
> for (i = 0; i < 6; i++) {
> pthread_create(&th[i], 0, thr, (void*)i);
> if (i%2==0)
> usleep(10000);
> }
> usleep(100000);
> return 0;
> }
>
>
> kasan: GPF could be caused by NULL-ptr deref or user memory
> accessgeneral protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
> Modules linked in:
> CPU: 0 PID: 8491 Comm: syz-executor Not tainted 4.4.0-rc8+ #217
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
> 01/01/2011
> task: ffff8800631c8000 ti: ffff880065380000 task.ti: ffff880065380000
> RIP: 0010:[<ffffffff8125fa5e>] [<ffffffff8125fa5e>]
> native_set_debugreg+0x2e/0x40
> RSP: 0018:ffff880065387a88 EFLAGS: 00000097
> RAX: ffff8800631c8000 RBX: ffff880063423478 RCX: ffff8800631c87c8
> RDX: 0000000000000000 RSI: 400ed35ee91c136b RDI: 0000000000000006
> RBP: ffff880065387a88 R08: 0000000000000001 R09: 0000000000000002
> R10: 0000000000000001 R11: 0000000000000001 R12: 1ffffffff0e09f6d
> R13: ffff880063420030 R14: ffff880063420000 R15: ffff88006342002c
> FS: 00007f8ed68a7700(0000) GS:ffff88003ec00000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 0000000001710000 CR3: 000000006486d000 CR4: 00000000000026f0
> DR0: 7e4b3b57e86b6a5d DR1: 0c294aa372a10dcf DR2: d8c752a700446dfc
> DR3: 6b54b5789d89db00 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Stack:
> ffff880065387c10 ffffffff8106c3a6 ffffffff81067de4 ffff880065387b38
> 0000000000000000 00000000002794c8 ffff880065380008 0000001b540f2184
> 0000000000000000 1ffff1000ca70001 ffff880065380000 ffff880063421ac8
> Call Trace:
> [< inline >] set_debugreg ./arch/x86/include/asm/paravirt.h:45
> [< inline >] vcpu_enter_guest arch/x86/kvm/x86.c:6532
> [< inline >] vcpu_run arch/x86/kvm/x86.c:6660
> [<ffffffff8106c3a6>] kvm_arch_vcpu_ioctl_run+0x47b6/0x5820
> arch/x86/kvm/x86.c:6818
> [<ffffffff8101cf61>] kvm_vcpu_ioctl+0x5f1/0xd00
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:2375
> [< inline >] vfs_ioctl fs/ioctl.c:43
> [<ffffffff817b36b1>] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:607
> [< inline >] SYSC_ioctl fs/ioctl.c:622
> [<ffffffff817b3eff>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
> [<ffffffff85e745b6>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> Code: 07 48 89 e5 77 27 89 ff ff 24 fd c0 25 f3 85 0f 23 fe 5d c3 0f
> 23 c6 5d c3 0f 23 ce 5d c3 0f 23 d6 5d c3 0f 23 de 5d c3 0f 23 f6 <5d>
> c3 0f 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 83 ff
> RIP [<ffffffff8125fa5e>] native_set_debugreg+0x2e/0x40
> ./arch/x86/include/asm/debugreg.h:65
> RSP <ffff880065387a88>
> ---[ end trace 94251fd7c32f126a ]---
>
>
> On commit b06f3a168cdcd80026276898fd1fee443ef25743 (Jan 6).
>
The only place native_set_debugreg references memory is a jmpq
instruction (6th instruction into the function) that handles the C
switch statement then jumps to set the debugreg. RDI (edi) is set to
6, so someone was setting debugreg 6 (probably with garbage status).
I guess this hardware GPF'd when someone tried to write to dr6.
native_set_debugreg
push rbp
cmp 7,edi
mov rsp,rbp
ja +0x41
move edi,edi
jmpq ptr @(rdi,8)
then several mov rsi, db#(0-7)
Interesting it crashes when someone is writing to DR6. I have already
reported this issue.
Jeff
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