linux-kernel - Re: [PATCH][next] selftests: kvm: fix shift of 32 bit unsigned int more than 32 bits

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Message-ID: <637ed8cb-4503-40eb-9731-eb56e6b1cd93@gmail.com>
Date: Thu, 23 May 2024 16:37:07 +0100
From: "Colin King (gmail)" <colin.i.king@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] selftests: kvm: fix shift of 32 bit unsigned int
 more than 32 bits

On 23/05/2024 16:35, Dan Carpenter wrote:
> On Thu, May 23, 2024 at 12:38:02PM +0100, Colin Ian King wrote:
>> Currrentl a 32 bit 1u value is being shifted more than 32 bits causing
>> overflow and incorrect checking of bits 32-63. Fix this by using the
>> BIT_ULL macro for shifting bits.
>>
>> Detected by cppcheck:
>> sev_init2_tests.c:108:34: error: Shifting 32-bit value by 63 bits is
>> undefined behaviour [shiftTooManyBits]
>>
>> Fixes: dfc083a181ba ("selftests: kvm: add tests for KVM_SEV_INIT2")
>> Signed-off-by: Colin Ian King <colin.i.king@...il.com>
>> ---
>>   tools/testing/selftests/kvm/x86_64/sev_init2_tests.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/kvm/x86_64/sev_init2_tests.c b/tools/testing/selftests/kvm/x86_64/sev_init2_tests.c
>> index 7a4a61be119b..ea09f7a06aa4 100644
>> --- a/tools/testing/selftests/kvm/x86_64/sev_init2_tests.c
>> +++ b/tools/testing/selftests/kvm/x86_64/sev_init2_tests.c
>> @@ -105,11 +105,11 @@ void test_features(uint32_t vm_type, uint64_t supported_features)
>>   	int i;
>>   
>>   	for (i = 0; i < 64; i++) {
>> -		if (!(supported_features & (1u << i)))
>> +		if (!(supported_features & BIT_ULL(i)))
>>   			test_init2_invalid(vm_type,
>>   				&(struct kvm_sev_init){ .vmsa_features = BIT_ULL(i) },
>>   				"unknown feature");
>> -		else if (KNOWN_FEATURES & (1u << i))
>> +		else if (KNOWN_FEATURES & BIT_ULL(u))
>                                                    ^
> Should be i.  How does this build?  :P

good catch, I sent the wrong one :-(
> 
> regards,
> dan carpenter
>