linux-kernel - Re: [PATCH] KVM: arm64: Fix shift-out-of-bounds bug

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Message-ID: <ab5ef80d-0e74-4a39-ba76-536b7d095b40@redhat.com>
Date: Thu, 17 Oct 2024 08:46:22 +1000
From: Gavin Shan <gshan@...hat.com>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>,
 Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
 Zenghui Yu <yuzenghui@...wei.com>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix shift-out-of-bounds bug

On 10/17/24 5:57 AM, Ilkka Koskinen wrote:
> Fix a shift-out-of-bounds bug reported by UBSAN when running
> VM with MTE enabled host kernel.
> 
> UBSAN: shift-out-of-bounds in arch/arm64/kvm/sys_regs.c:1988:14
> shift exponent 33 is too large for 32-bit type 'int'
> CPU: 26 UID: 0 PID: 7629 Comm: qemu-kvm Not tainted 6.12.0-rc2 #34
> Hardware name: IEI NF5280R7/Mitchell MB, BIOS 00.00. 2024-10-12 09:28:54 10/14/2024
> Call trace:
>   dump_backtrace+0xa0/0x128
>   show_stack+0x20/0x38
>   dump_stack_lvl+0x74/0x90
>   dump_stack+0x18/0x28
>   __ubsan_handle_shift_out_of_bounds+0xf8/0x1e0
>   reset_clidr+0x10c/0x1c8
>   kvm_reset_sys_regs+0x50/0x1c8
>   kvm_reset_vcpu+0xec/0x2b0
>   __kvm_vcpu_set_target+0x84/0x158
>   kvm_vcpu_set_target+0x138/0x168
>   kvm_arch_vcpu_ioctl_vcpu_init+0x40/0x2b0
>   kvm_arch_vcpu_ioctl+0x28c/0x4b8
>   kvm_vcpu_ioctl+0x4bc/0x7a8
>   __arm64_sys_ioctl+0xb4/0x100
>   invoke_syscall+0x70/0x100
>   el0_svc_common.constprop.0+0x48/0xf0
>   do_el0_svc+0x24/0x38
>   el0_svc+0x3c/0x158
>   el0t_64_sync_handler+0x120/0x130
>   el0t_64_sync+0x194/0x198
> 
> Fixes: 7af0c2534f4c ("KVM: arm64: Normalize cache configuration")
> Cc: stable@...r.kernel.org
> Signed-off-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
> ---
>   arch/arm64/kvm/sys_regs.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

Reviewed-by: Gavin Shan <gshan@...hat.com>

> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 375052d8cd22..665c576faba3 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1994,7 +1994,7 @@ static u64 reset_clidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>   	 * one cache line.
>   	 */
>   	if (kvm_has_mte(vcpu->kvm))
> -		clidr |= 2 << CLIDR_TTYPE_SHIFT(loc);
> +		clidr |= 2UL << CLIDR_TTYPE_SHIFT(loc);
>   

Nit: It's more precise to have 2ULL since the type of @clidr is u64,
equivalent to 'unsigned long long' on arm64. The pattern ULL has been
used in reset_mpidr().

>   	__vcpu_sys_reg(vcpu, r->reg) = clidr;
>   

Thanks,
Gavin