Re: [PATCH 1/1] AMD64_EDAC: Fix incorrect wrap arounds due to leftshift beyond 32 bits.

[Aravind Gopalakrishnan]

On 8/23/2013 4:37 PM, Borislav Petkov wrote:
> On Mon, Aug 19, 2013 at 07:27:52PM -0500, Aravind Gopalakrishnan wrote:
> > Link to the bug report:
> > http://marc.info/?l=linux-edac&m=137692201732220&w=2
> >
> > dct_base and dct_limit obtain 32 bit register values when they read their
> > respective pci config space registers. A left shift beyond 32 bits will
> > cause them to wrap around. Similar case for chan_addr as can be seen from
> > the bug report. In the patch, we rectify this by casting chan_addr to u64
> > and by comparing dct_base and dct_limit against (sys_addr >> 27)
> >
> > Tested on F15h, M30h with ECC turned on and works fine.
> >
> > Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
> >
> > diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
> > index b86228c..eb4793e 100644
> > --- a/drivers/edac/amd64_edac.c
> > +++ b/drivers/edac/amd64_edac.c
> > @@ -1558,11 +1558,12 @@ static int f15_m30h_match_to_this_node(struct amd64_pvt *pvt, unsigned range,
> >   	}
> >   
> >   	/* Verify sys_addr is within DCT Range. */
> > -	dct_base = (dct_sel_baseaddr(pvt) << 27);
> > -	dct_limit = (((dct_cont_limit_reg >> 11) & 0x1FFF) << 27) | 0x7FFFFFF;
> > +	dct_base = dct_sel_baseaddr(pvt);
> This can't be correct.
>
> So the original patch takes the shifted dct_base while your change
> doesn't anymore...
>
> > +	dct_limit = (dct_cont_limit_reg >> 11) & 0x1FFF;
> >   
> >   	if (!(dct_cont_base_reg & BIT(0)) &&
> > -	    !(dct_base <= sys_addr && dct_limit >= sys_addr))
> > +	    !(dct_base <= (sys_addr >> 27) &&
> > +	      dct_limit >= (sys_addr >> 27)))
> ... and while this comparison shifts sys_addr to use the proper bits,
> the code does this assignment later:
>
> 	chan_offset = dct_base;
>
> Now, chan_offset has the << 27 version of dct_base which makes the following
> calculation wrong:
>
> 	chan_addr = sys_addr - chan_offset;
Oops. my apologies.
> because sys_addr is the full 64-bit, unshifted value.
>
> The right thing to do would be to do:
>
> 	chan_offset = dct_base << 27;
>
> Or am I missing something?
No, you are right.

I am re-sending the patch.

Thanks,
-Aravind.


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