Re: include/linux/kvm_host.h:488 suspicious rcu_dereference_check() usage!

[Paolo Bonzini]

On 20/09/2015 18:48, Borislav Petkov wrote:
> [26421.584526] walk_shadow_page_get_mmio_spte: detect reserved bits on spte, addr 0xb8000, dump hierarchy:
> [26421.593927] ------ spte 0x3e5a22027 level 4.
> [26421.598228] ------ spte 0x38a00b027 level 3.
> [26421.602505] ------ spte 0x387334027 level 2.
> [26421.602506] ------ spte 0xffff0000000b8f67 level 1.
> [26421.602506] ------------[ cut here ]------------
> [26421.602530] WARNING: CPU: 2 PID: 17000 at arch/x86/kvm/mmu.c:3385 handle_mmio_page_fault.part.93+0x1a/0x20 [kvm]()
> [26421.602550] Modules linked in: tun sha256_ssse3 sha256_generic drbg binfmt_misc ipv6 vfat fat fuse dm_crypt dm_mod kvm_amd kvm crc32_pclmul aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd fam15h_power amd64_edac_mod k10temp edac_core amdkfd amd_iommu_v2 radeon acpi_cpufreq
> [26421.602552] CPU: 2 PID: 17000 Comm: qemu-system-i38 Not tainted 4.3.0-rc1+ #1
> [26421.602553] 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
> [26421.602555]  ffffffffa02fc7d2 ffff880386c0fb80 ffffffff812c8c2a 0000000000000000
> [26421.602556]  ffff880386c0fbb8 ffffffff81053e55 ffff880429ff8000 000000000000000f
> [26421.602558]  00000000000b8000 0000000000000000 00000000ffffffff ffff880386c0fbc8
> [26421.602558] Call Trace:
> [26421.602564]  [<ffffffff812c8c2a>] dump_stack+0x4e/0x84
> [26421.602566]  [<ffffffff81053e55>] warn_slowpath_common+0x95/0xe0
> [26421.602567]  [<ffffffff81053f5a>] warn_slowpath_null+0x1a/0x20
> [26421.602577]  [<ffffffffa02cf73a>] handle_mmio_page_fault.part.93+0x1a/0x20 [kvm]
> [26421.602587]  [<ffffffffa02d5ff1>] tdp_page_fault+0x231/0x290 [kvm]
> [26421.602596]  [<ffffffffa02bf32e>] ? emulator_pio_in_out+0x6e/0xf0 [kvm]
> [26421.602606]  [<ffffffffa02d1676>] kvm_mmu_page_fault+0x36/0x240 [kvm]
> [26421.602609]  [<ffffffffa0357a25>] ? svm_set_cr0+0x95/0xc0 [kvm_amd]
> [26421.602610]  [<ffffffffa035671e>] pf_interception+0xde/0x1d0 [kvm_amd]
> [26421.602613]  [<ffffffffa0358cb1>] handle_exit+0x181/0xa70 [kvm_amd]
> [26421.602622]  [<ffffffffa02c748b>] ? kvm_arch_vcpu_ioctl_run+0x68b/0x1730 [kvm]
> [26421.602631]  [<ffffffffa02c74f6>] kvm_arch_vcpu_ioctl_run+0x6f6/0x1730 [kvm]
> [26421.602640]  [<ffffffffa02c748b>] ? kvm_arch_vcpu_ioctl_run+0x68b/0x1730 [kvm]
> [26421.602642]  [<ffffffff81082afb>] ? preempt_count_sub+0x9b/0xf0
> [26421.602644]  [<ffffffff816c144f>] ? mutex_lock_killable_nested+0x26f/0x490
> [26421.602645]  [<ffffffff81082afb>] ? preempt_count_sub+0x9b/0xf0
> [26421.602651]  [<ffffffffa02ae7e8>] kvm_vcpu_ioctl+0x358/0x710 [kvm]
> [26421.602654]  [<ffffffff811a0615>] ? __fget+0x5/0x210
> [26421.602655]  [<ffffffff811a0711>] ? __fget+0x101/0x210
> [26421.602657]  [<ffffffff81194a54>] do_vfs_ioctl+0x2f4/0x560
> [26421.602658]  [<ffffffff811a0889>] ? __fget_light+0x29/0x90
> [26421.602660]  [<ffffffff81194d0c>] SyS_ioctl+0x4c/0x90
> [26421.602661]  [<ffffffff816c495b>] entry_SYSCALL_64_fastpath+0x16/0x73
> [26421.602663] ---[ end trace 37901c8686d84de6 ]---
> 
> Any ideas?

I am sending a patch for the RCU splat, for this I'll take a look later
this week.

Paolo
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