linux-kernel - Re: [PATCH] KVM: x86/mmu: Check that root is valid/loaded when pre-faulting SPTEs

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Message-ID: <36021c91-44c6-48fc-9a63-7ff2301e200c@intel.com>
Date: Tue, 23 Jul 2024 14:48:38 +1200
From: "Huang, Kai" <kai.huang@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
	<pbonzini@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<syzbot+23786faffb695f17edaa@...kaller.appspotmail.com>
Subject: Re: [PATCH] KVM: x86/mmu: Check that root is valid/loaded when
 pre-faulting SPTEs



On 23/07/2024 12:02 pm, Sean Christopherson wrote:
> Error out if kvm_mmu_reload() fails when pre-faulting memory, as trying to
> fault-in SPTEs will fail miserably due to root.hpa pointing at garbage.
> 
> Note, kvm_mmu_reload() can return -EIO and thus trigger the WARN on -EIO
> in kvm_vcpu_pre_fault_memory(), but all such paths also WARN, i.e. the
> WARN isn't user-triggerable and won't run afoul of warn-on-panic because
> the kernel would already be panicking.
> 
>    BUG: unable to handle page fault for address: 000029ffffffffe8
>    #PF: supervisor read access in kernel mode
>    #PF: error_code(0x0000) - not-present page
>    PGD 0 P4D 0
>    Oops: Oops: 0000 [#1] PREEMPT SMP
>    CPU: 22 PID: 1069 Comm: pre_fault_memor Not tainted 6.10.0-rc7-332d2c1d713e-next-vm #548
>    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
>    RIP: 0010:is_page_fault_stale+0x3e/0xe0 [kvm]
>    RSP: 0018:ffffc9000114bd48 EFLAGS: 00010206
>    RAX: 00003fffffffffc0 RBX: ffff88810a07c080 RCX: ffffc9000114bd78
>    RDX: ffff88810a07c080 RSI: ffffea0000000000 RDI: ffff88810a07c080
>    RBP: ffffc9000114bd78 R08: 00007fa3c8c00000 R09: 8000000000000225
>    R10: ffffea00043d7d80 R11: 0000000000000000 R12: ffff88810a07c080
>    R13: 0000000100000000 R14: ffffc9000114be58 R15: 0000000000000000
>    FS:  00007fa3c9da0740(0000) GS:ffff888277d80000(0000) knlGS:0000000000000000
>    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>    CR2: 000029ffffffffe8 CR3: 000000011d698000 CR4: 0000000000352eb0
>    Call Trace:
>     <TASK>
>     kvm_tdp_page_fault+0xcc/0x160 [kvm]
>     kvm_mmu_do_page_fault+0xfb/0x1f0 [kvm]
>     kvm_arch_vcpu_pre_fault_memory+0xd0/0x1a0 [kvm]
>     kvm_vcpu_ioctl+0x761/0x8c0 [kvm]
>     __x64_sys_ioctl+0x82/0xb0
>     do_syscall_64+0x5b/0x160
>     entry_SYSCALL_64_after_hwframe+0x4b/0x53
>     </TASK>
>    Modules linked in: kvm_intel kvm
>    CR2: 000029ffffffffe8
>    ---[ end trace 0000000000000000 ]---
> 
> Fixes: 6e01b7601dfe ("KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()")
> Reported-by: syzbot+23786faffb695f17edaa@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/0000000000002b84dc061dd73544@google.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---

Reviewed-by: Kai Huang <kai.huang@...el.com>