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SubjectRe: [PATCH 2/3] scsi: megaraid_sas: check user-provided offsets
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On Sun, 2021-01-03 at 19:49 +0100, Arnd Bergmann wrote:
> On Sun, Jan 3, 2021 at 6:00 PM James Bottomley <jejb@linux.ibm.com>
> wrote:
> > On Sun, 2021-01-03 at 17:26 +0100, Arnd Bergmann wrote:
> > [...]
> > > @@ -8209,7 +8208,7 @@ megasas_mgmt_fw_ioctl(struct
> > > megasas_instance
> > > *instance,
> > > if (instance->consistent_mask_64bit)
> > > put_unaligned_le64(sense_handle,
> > > sense_ptr);
> > > else
> > > - put_unaligned_le32(sense_handle,
> > > sense_ptr);
> > > + put_unaligned_le64(sense_handle,
> > > sense_ptr);
> > > }
> >
> > This hunk can't be right. It effectively means removing the if.
>
> I'm just trying to restore the state before the regression introduced
> in my 381d34e376e3 ("scsi: megaraid_sas: Check user-provided
> offsets").
>
> The old code always stored 'sizeof(long)' bytes into sense_ptr,
> regardless of instance->consistent_mask_64bit, but it would truncate
> the address to 32 bit if that was cleared. This was clearly bogus
> and I tried to make it do something more meaningful, only storing
> 8 bytes into the structure if it was configured for 64-bit DMA,
> regardless of the capabilities of the kernel.

Heh, well, all this depends on how the firmware interprets the pointer,
for which we don't seem to have a manual. Instinct tells me the flag
MFI_FRAME_SENSE64 is what does this and that's conditioned on the same
if clause 100 lines above this, so the fix your proposing would still
seem to be wrong, because I think when that flag is not set, the device
expects the sense pointer to be 32 bit.

> > However, the if is needed because sense_handle is a dma_addr_t
> > which can be either 32 or 64 bit. What about changing the if to
> >
> > if (sizeof(dma_addr_t) == 8)
> >
> > instead?
>
> That would not be useful either, the device surely does not care
> if the kernel supports 64-bit DMA. What we'd really need here is
> someone with access to the interface specifications to see how
> many bytes should be stored in the structure. I suspect always
> storing 64 bits (as my patch does) is correct, and would send a
> proper patch to remove the if() if Phil confirms that my test
> patch fixes the regression.

Well, as I said above, I'm speculating the device does what we tell it,
and whether to use 32 or 64 bits for the sense pointer definitely seems
to be a flag the driver controls ... we really need someone with access
to the programming manual to tell us if this speculation is accurate,
though.

James


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