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

[Ilkka Koskinen <ilkka@os.amperecomputing.com>]

Hi Gavin,

On Wed, 16 Oct 2024, Gavin Shan wrote:
> 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@vger.kernel.org
>> Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
>> ---
>>   arch/arm64/kvm/sys_regs.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>
> Reviewed-by: Gavin Shan <gshan@redhat.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().

That's a good catch. I change it and submit v2 right away.

Cheers, Ilkka

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