Re: [PATCH] kvm: x86: move tracepoints outside extended quiescent state

[Borislav Petkov <bp@alien8.de>]

On Thu, Dec 10, 2015 at 07:15:19PM +0100, Paolo Bonzini wrote:
> Yeah, wait_lapic_expire also have to be moved before __kvm_guest_enter.

Yeah, v2 doesn't splat on the Intel box anymore but the AMD box still
has, and it is a different problem. With the v2 applied, it still
explodes, see below.

And I'm willing to bet good money on that shadow pages fun. The

[  959.466549] kernel tried to execute NX-protected page - exploit attempt? (uid: 1000)

line basically says that we're pagefaulting when trying to fetch
instructions, i.e., we're trying to execute something from a page, rIP
points to 0xffff8800b9f9bdf0 and that is most likely a page belonging to
kvm, which, however, is for some reason not executable (anymore?).

Could it have anything to do with that zapping of shadow pages, per
chance?

Can I disable the zapping and see if it still triggers? Or should I try
modprobing kvm with "npt=0" or so?

/me goes and tries it...

Nope, that doesn't help - it still splats.

Hmmm...

[  849.272337] kvm: zapping shadow pages for mmio generation wraparound
[  933.813871] kvm: zapping shadow pages for mmio generation wraparound
[  959.466549] kernel tried to execute NX-protected page - exploit attempt? (uid: 1000)
[  959.474369] BUG: unable to handle kernel paging request at ffff8800b9f9bdf0
[  959.481407] IP: [<ffff8800b9f9bdf0>] 0xffff8800b9f9bdf0
[  959.486677] PGD 2d7e067 PUD 43efff067 PMD 80000000b9e001e3 
[  959.492338] Oops: 0011 [#1] PREEMPT SMP 
[  959.496340] Modules linked in: tun sha256_ssse3 sha256_generic drbg binfmt_misc ipv6 vfat fat fuse dm_crypt dm_mod kvm_amd kvm irqbypass crc32_pclmul aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd amd64_edac_mod fam15h_power k10temp edac_mce_amd amdkfd amd_iommu_v2 radeon acpi_cpufreq
[  959.524023] CPU: 3 PID: 3798 Comm: qemu-system-x86 Not tainted 4.4.0-rc4+ #8
[  959.531127] Hardware name: To be filled by O.E.M. To be filled by O.E.M./M5A97 EVO R2.0, BIOS 1503 01/16/2013
[  959.541113] task: ffff8800b7ca5e00 ti: ffff8800b9f98000 task.ti: ffff8800b9f98000
[  959.548625] RIP: 0010:[<ffff8800b9f9bdf0>]  [<ffff8800b9f9bdf0>] 0xffff8800b9f9bdf0
[  959.556338] RSP: 0018:ffff8800b9f9bde0  EFLAGS: 00010206
[  959.561676] RAX: 000003993d0f82ee RBX: ffff8800b7d48000 RCX: 0000000000000001
[  959.568844] RDX: 0000039900000000 RSI: ffffffffa02bdc7b RDI: ffff8800b7d48000
[  959.576010] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[  959.583177] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
[  959.590346] R13: ffff8800b7d48000 R14: 0000000000000000 R15: 0000000000000000
[  959.597513] FS:  00007f7fae580700(0000) GS:ffff88042cc00000(0000) knlGS:0000000000000000
[  959.605643] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  959.611414] CR2: ffff8800b9f9bdf0 CR3: 000000041b5fe000 CR4: 00000000000406e0
[  959.618579] Stack:
[  959.620607]  ffffffffa02d5e17 ffff8800b7d48000 ffff8800b9f9be08 ffffffffa02bdb1f
[  959.628104]  0000000000000000 ffff8800b9f9be98 ffffffffa02bdc7b ffff8804242a4400
[  959.635601]  0000000000000070 0000000000004000 ffffffff81a3c1e0 ffff8800b7ca5e00
[  959.643114] Call Trace:
[  959.645599]  [<ffffffffa02d5e17>] ? kvm_arch_vcpu_put+0x17/0x40 [kvm]
[  959.652081]  [<ffffffffa02bdb1f>] ? vcpu_put+0x1f/0x60 [kvm]
[  959.657782]  [<ffffffffa02bdc7b>] ? kvm_vcpu_ioctl+0x11b/0x6f0 [kvm]
[  959.664169]  [<ffffffff811a0930>] ? do_vfs_ioctl+0x2e0/0x540
[  959.669855]  [<ffffffff811ac8e9>] ? __fget_light+0x29/0x90
[  959.675364]  [<ffffffff811a0bdc>] ? SyS_ioctl+0x4c/0x90
[  959.680618]  [<ffffffff816e2d5b>] ? entry_SYSCALL_64_fastpath+0x16/0x6f
[  959.687263] Code: 00 00 00 06 02 01 00 00 00 00 00 e0 bd f9 b9 00 88 ff ff 18 00 00 00 00 00 00 00 17 5e 2d a0 ff ff ff ff 00 80 d4 b7 00 88 ff ff <08> be f9 b9 00 88 ff ff 1f db 2b a0 ff ff ff ff 00 00 00 00 00 
[  959.707506] RIP  [<ffff8800b9f9bdf0>] 0xffff8800b9f9bdf0
[  959.712862]  RSP <ffff8800b9f9bde0>
[  959.716373] CR2: ffff8800b9f9bdf0
[  959.735764] ---[ end trace 6826bd13f6e235cd ]---
[  959.740465] note: qemu-system-x86[3798] exited with preempt_count 1
[  979.163010] kvm: zapping shadow pages for mmio generation wraparound

-- 
Regards/Gruss,
    Boris.

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