Subject: Re: [PATCH] KVM: PPC: Book3S HV: XIVE: Fix possible oops when accessing ESB page

From: Greg Kurz <[email-masked]>
Date: Thu, 5 Nov 2020 18:41:22 +0100

On Thu, 5 Nov 2020 14:47:13 +0100
Cédric Le Goater <[email-masked]> wrote:

> When accessing the ESB page of a source interrupt, the fault handler
> will retrieve the page address from the XIVE interrupt 'xive_irq_data'
> structure. If the associated KVM XIVE interrupt is not valid, that is
> not allocated at the HW level for some reason, the fault handler will
> dereference a NULL pointer leading to the oops below :
> 
>     WARNING: CPU: 40 PID: 59101 at arch/powerpc/kvm/book3s_xive_native.c:259 xive_native_esb_fault+0xe4/0x240 [kvm]
>     CPU: 40 PID: 59101 Comm: qemu-system-ppc Kdump: loaded Tainted: G        W        --------- -  - 4.18.0-240.el8.ppc64le #1
>     NIP:  c00800000e949fac LR: c00000000044b164 CTR: c00800000e949ec8
>     REGS: c000001f69617840 TRAP: 0700   Tainted: G        W        --------- -  -  (4.18.0-240.el8.ppc64le)
>     MSR:  9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 44044282  XER: 00000000
>     CFAR: c00000000044b160 IRQMASK: 0
>     GPR00: c00000000044b164 c000001f69617ac0 c00800000e96e000 c000001f69617c10
>     GPR04: 05faa2b21e000080 0000000000000000 0000000000000005 ffffffffffffffff
>     GPR08: 0000000000000000 0000000000000001 0000000000000000 0000000000000001
>     GPR12: c00800000e949ec8 c000001ffffd3400 0000000000000000 0000000000000000
>     GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>     GPR20: 0000000000000000 0000000000000000 c000001f5c065160 c000000001c76f90
>     GPR24: c000001f06f20000 c000001f5c065100 0000000000000008 c000001f0eb98c78
>     GPR28: c000001dcab40000 c000001dcab403d8 c000001f69617c10 0000000000000011
>     NIP [c00800000e949fac] xive_native_esb_fault+0xe4/0x240 [kvm]
>     LR [c00000000044b164] __do_fault+0x64/0x220
>     Call Trace:
>     [c000001f69617ac0] [0000000137a5dc20] 0x137a5dc20 (unreliable)
>     [c000001f69617b50] [c00000000044b164] __do_fault+0x64/0x220
>     [c000001f69617b90] [c000000000453838] do_fault+0x218/0x930
>     [c000001f69617bf0] [c000000000456f50] __handle_mm_fault+0x350/0xdf0
>     [c000001f69617cd0] [c000000000457b1c] handle_mm_fault+0x12c/0x310
>     [c000001f69617d10] [c00000000007ef44] __do_page_fault+0x264/0xbb0
>     [c000001f69617df0] [c00000000007f8c8] do_page_fault+0x38/0xd0
>     [c000001f69617e30] [c00000000000a714] handle_page_fault+0x18/0x38
>     Instruction dump:
>     40c2fff0 7c2004ac 2fa90000 409e0118 73e90001 41820080 e8bd0008 7c2004ac
>     7ca90074 39400000 915c0000 7929d182 <0b090000> 2fa50000 419e0080 e89e0018
>     ---[ end trace 66c6ff034c53f64f ]---
>     xive-kvm: xive_native_esb_fault: accessing invalid ESB page for source 8 !
> 
> Fix that by checking the validity of the KVM XIVE interrupt structure.
> 
> Reported-by: Greg Kurz <[email-masked]>
> Signed-off-by: Cédric Le Goater <[email-masked]>
> ---

Looks sane to me. QEMU still crashes on SIGBUS but no more oops at least.

Tested-by: Greg Kurz <[email-masked]>

>  arch/powerpc/kvm/book3s_xive_native.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/book3s_xive_native.c b/arch/powerpc/kvm/book3s_xive_native.c
> index d0c2db0e07fa..a59a94f02733 100644
> --- a/arch/powerpc/kvm/book3s_xive_native.c
> +++ b/arch/powerpc/kvm/book3s_xive_native.c
> @@ -251,6 +251,13 @@ static vm_fault_t xive_native_esb_fault(struct vm_fault *vmf)
>  	}
>  
>  	state = &sb->irq_state[src];
> +
> +	/* Some sanity checking */
> +	if (!state->valid) {
> +		pr_devel("%s: source %lx invalid !\n", __func__, irq);
> +		return VM_FAULT_SIGBUS;
> +	}
> +
>  	kvmppc_xive_select_irq(state, &hw_num, &xd);
>  
>  	arch_spin_lock(&sb->lock);