linux-kernel - Re: [PATCH] perf/x86/intel/uncore: fix integer overflow on shift of a u32 integer

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Date:   Wed, 2 Oct 2019 13:38:22 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86/intel/uncore: fix integer overflow on shift of a
 u32 integer

On 02/10/2019 13:23, Mark Rutland wrote:
> On Wed, Oct 02, 2019 at 12:55:45PM +0100, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> Shifting the u32 integer result of (pci_dword & SNR_IMC_MMIO_BASE_MASK)
>> will end up with an overflow when pci_dword greater than 0x1ff. Fix this
>> by casting pci_dword to a resource_size_t before masking and shifting it.
>>
>> Addresses-Coverity: ("Unintentional integer overflow")
> 
> I don't see that tag in Documentation/process/submitting-patches.rst ;)
> 
> IIUC this is unintented truncation of the upper bits due to missing type
> promotion before the shift, rather than overflow (i.e. the value
> wrapping across addition/subtraction), so I think the wording is
> slightly misleading.
> 
> Does coverity call that integer overflow?

Coverity calls it "Unintentional integer overflow". I suspect Coverity
first spots the overflow before the truncation occurs and so flags that
up as the root cause.

> 
> It might be better to say:
> 
> | [PATCH] perf/x86/intel/uncore: don't truncate upper bits of address
> |
> | Shifting the u32 integer result of (pci_dword & SNR_IMC_MMIO_BASE_MASK)
> | by 23 will throw away the upper 23 bits of the potentially 64-bit
> | address. Fix this by casting pci_dword to a resource_size_t before
> | masking and shifting it.
> |
> | Found by coverity ("Unintentional integer overflow").
> 
> Otherwise, the patch looks fine to me:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> 
> Thanks,
> Mark.
> 
>> Fixes: ee49532b38dd ("perf/x86/intel/uncore: Add IMC uncore support for Snow Ridge")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  arch/x86/events/intel/uncore_snbep.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
>> index b10a5ec79e48..ed69df1340d9 100644
>> --- a/arch/x86/events/intel/uncore_snbep.c
>> +++ b/arch/x86/events/intel/uncore_snbep.c
>> @@ -4415,7 +4415,7 @@ static void snr_uncore_mmio_init_box(struct intel_uncore_box *box)
>>  		return;
>>  
>>  	pci_read_config_dword(pdev, SNR_IMC_MMIO_BASE_OFFSET, &pci_dword);
>> -	addr = (pci_dword & SNR_IMC_MMIO_BASE_MASK) << 23;
>> +	addr = ((resource_size_t)pci_dword & SNR_IMC_MMIO_BASE_MASK) << 23;
>>  
>>  	pci_read_config_dword(pdev, SNR_IMC_MMIO_MEM0_OFFSET, &pci_dword);
>>  	addr |= (pci_dword & SNR_IMC_MMIO_MEM0_MASK) << 12;
>> -- 
>> 2.20.1
>>