Re: [PATCH v5 3/3] hw/nvme: add nvme management interface model

[Klaus Jensen <its@irrelevant.dk>]

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On Sep 12 13:50, Andrew Jeffery wrote:
> Hi Klaus,
> 
> On Tue, 2023-09-05 at 10:38 +0200, Klaus Jensen wrote:
> > > 
> > > +static void nmi_handle_mi_config_get(NMIDevice *nmi, NMIRequest
> > > *request)
> > > +{
> > > +    uint32_t dw0 = le32_to_cpu(request->dw0);
> > > +    uint8_t identifier = FIELD_EX32(dw0,
> > > NMI_CMD_CONFIGURATION_GET_DW0,
> > > +                                    IDENTIFIER);
> > > +    const uint8_t *buf;
> > > +
> > > +    static const uint8_t smbus_freq[4] = {
> > > +        0x00,               /* success */
> > > +        0x01, 0x00, 0x00,   /* 100 kHz */
> > > +    };
> > > +
> > > +    static const uint8_t mtu[4] = {
> > > +        0x00,       /* success */
> > > +        0x40, 0x00, /* 64 */
> > > +        0x00,       /* reserved */
> > > +    };
> > > +
> > > +    trace_nmi_handle_mi_config_get(identifier);
> > > +
> > > +    switch (identifier) {
> > > +    case NMI_CMD_CONFIGURATION_GET_SMBUS_FREQ:
> > > +        buf = smbus_freq;
> > > +        break;
> > > +
> > > +    case NMI_CMD_CONFIGURATION_GET_MCTP_TRANSMISSION_UNIT:
> > > +        buf = mtu;
> > > +        break;
> > > +
> > > +    default:
> > > +        nmi_set_parameter_error(nmi, 0x0, offsetof(NMIRequest,
> > > dw0));
> > > +        return;
> > > +    }
> > > +
> > > +    nmi_scratch_append(nmi, buf, sizeof(buf));
> > > +}
> 
> When I tried to build this patch I got:
> 
> ```
> In file included from /usr/include/string.h:535,
>                  from /home/andrew/src/qemu.org/qemu/include/qemu/osdep.h:112,
>                  from ../hw/nvme/nmi-i2c.c:12:
> In function ‘memcpy’,
>     inlined from ‘nmi_scratch_append’ at ../hw/nvme/nmi-i2c.c:80:5,
>     inlined from ‘nmi_handle_mi_config_get’ at ../hw/nvme/nmi-i2c.c:246:5,
>     inlined from ‘nmi_handle_mi’ at ../hw/nvme/nmi-i2c.c:266:9,
>     inlined from ‘nmi_handle’ at ../hw/nvme/nmi-i2c.c:313:9:
> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:29:10: error: ‘__builtin_memcpy’ forming offset [4, 7] is out of the bounds [0, 4] [-Werror=array-bounds=]
>    29 |   return __builtin___memcpy_chk (__dest, __src, __len,
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    30 |                                  __glibc_objsize0 (__dest));
>       |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~
> ```
> 
> It wasn't clear initially from the error that the source of the problem
> was the size associated with the source buffer, especially as there is
> some pointer arithmetic being done to derive `__dest`.
> 
> Anyway, what we're trying to express is that the size to copy from buf
> is the size of the array pointed to by buf. However, buf is declared as
> a pointer to uint8_t, which loses the length information. To fix that I
> think we need:
> 
> - const uint8_t *buf;
> + const uint8_t (*buf)[4];
> 
> and then:
> 
> - nmi_scratch_append(nmi, buf, sizeof(buf));
> + nmi_scratch_append(nmi, buf, sizeof(*buf));
> 
> Andrew
> 

Hi Andrew,

Nice (and important) catch! Just curious, are you massaging QEMU's build
system into adding additional checks or how did your compiler catch
this?

Thanks,
Klaus

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