linux-kernel - Re: arch/s390/kvm/gaccess.c:859 guest_range_to_gpas() error: uninitialized symbol 'prot'.

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Message-ID: <f27b0f3a-5e89-1fb1-ac23-ed896ec7150f@linux.ibm.com>
Date:   Wed, 17 Aug 2022 12:30:11 +0200
From:   Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>, kbuild@...ts.01.org
Cc:     lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: Re: arch/s390/kvm/gaccess.c:859 guest_range_to_gpas() error:
 uninitialized symbol 'prot'.

On 8/15/22 09:23, Dan Carpenter wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   69dac8e431af26173ca0a1ebc87054e01c585bcc
> commit: 7faa543df19bf62d4583a64d3902705747f2ad29 KVM: s390: gaccess: Refactor access address range check
> config: s390-randconfig-m031-20220812 (https://download.01.org/0day-ci/archive/20220814/202208140141.4uzWszG4-lkp@intel.com/config)
> compiler: s390-linux-gcc (GCC) 12.1.0
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> smatch warnings:
> arch/s390/kvm/gaccess.c:859 guest_range_to_gpas() error: uninitialized symbol 'prot'.
> 
> vim +/prot +859 arch/s390/kvm/gaccess.c
> 
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  831  static int guest_range_to_gpas(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  832  			       unsigned long *gpas, unsigned long len,
> 92c9632119b67f David Hildenbrand        2015-11-16  833  			       const union asce asce, enum gacc_mode mode)
> 2293897805c2fe Heiko Carstens           2014-01-01  834  {
> 2293897805c2fe Heiko Carstens           2014-01-01  835  	psw_t *psw = &vcpu->arch.sie_block->gpsw;
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  836  	unsigned int offset = offset_in_page(ga);
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  837  	unsigned int fragment_len;
> cde0dcfb5df1db David Hildenbrand        2016-05-31  838  	int lap_enabled, rc = 0;
> 6ae1574c2a24ee Christian Borntraeger    2017-06-07  839  	enum prot_type prot;
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  840  	unsigned long gpa;
> 2293897805c2fe Heiko Carstens           2014-01-01  841  
> 75a1812230ad7a Alexander Yarygin        2015-01-22  842  	lap_enabled = low_address_protection_enabled(vcpu, asce);
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  843  	while (min(PAGE_SIZE - offset, len) > 0) {
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  844  		fragment_len = min(PAGE_SIZE - offset, len);
> 2293897805c2fe Heiko Carstens           2014-01-01  845  		ga = kvm_s390_logical_to_effective(vcpu, ga);
> cde0dcfb5df1db David Hildenbrand        2016-05-31  846  		if (mode == GACC_STORE && lap_enabled && is_low_address(ga))
> cde0dcfb5df1db David Hildenbrand        2016-05-31  847  			return trans_exc(vcpu, PGM_PROTECTION, ga, ar, mode,
> cde0dcfb5df1db David Hildenbrand        2016-05-31  848  					 PROT_TYPE_LA);
> a752598254016d Heiko Carstens           2017-06-03  849  		if (psw_bits(*psw).dat) {
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  850  			rc = guest_translate(vcpu, ga, &gpa, asce, mode, &prot);
> 2293897805c2fe Heiko Carstens           2014-01-01  851  			if (rc < 0)
> 2293897805c2fe Heiko Carstens           2014-01-01  852  				return rc;
> 2293897805c2fe Heiko Carstens           2014-01-01  853  		} else {
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  854  			gpa = kvm_s390_real_to_abs(vcpu, ga);
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  855  			if (kvm_is_error_gpa(vcpu->kvm, gpa))
> cde0dcfb5df1db David Hildenbrand        2016-05-31  856  				rc = PGM_ADDRESSING;
>                                                                                         ^^^^^^^^^^^^^^^^^^^^
> 
> "rc" set but "prot" not initialized.

prot is only used in case of PGM_PROTECTION.
Because of that, we could initialize prot to an arbitrary value, but that seems misleading and a bit ugly to me.
Alternatively, we could introduce a PROT_NONE.
Or we do nothing, since there is no actual problem.
@Janosch, @Claudio, what do you think?

> 
> 2293897805c2fe Heiko Carstens           2014-01-01  857  		}
> cde0dcfb5df1db David Hildenbrand        2016-05-31  858  		if (rc)
> 6ae1574c2a24ee Christian Borntraeger    2017-06-07 @859  			return trans_exc(vcpu, rc, ga, ar, mode, prot);
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  860  		if (gpas)
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  861  			*gpas++ = gpa;
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  862  		offset = 0;
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  863  		ga += fragment_len;
> 7faa543df19bf6 Janis Schoetterl-Glausch 2021-11-26  864  		len -= fragment_len;
> 2293897805c2fe Heiko Carstens           2014-01-01  865  	}
> 2293897805c2fe Heiko Carstens           2014-01-01  866  	return 0;
> 2293897805c2fe Heiko Carstens           2014-01-01  867  }
>