Re: [5.3] ucc_geth: Fix to avoid IS_ERR_VALUE abuses and dead code on 64bit systems.

On Monday, August 8, 2016 3:49:22 PM CEST David Laight wrote:

From: Arnd Bergmann

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Sent: 08 August 2016 16:13

On Monday, August 8, 2016 2:49:11 PM CEST David Laight wrote:

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If qe_muram_alloc will return any error, Then IS_ERR_VALUE will always
return 0. it'll not call ucc_fast_free for any failure. Inside 'if code'
will be a dead code on 64bit. Even qe_muram_addr will return wrong
virtual address. Which can cause an error.

 kfree((void *)ugeth->tx_bd_ring_offset[i]);

Erm, kfree() isn't the right function for things allocated by qe_muram_alloc().

I still thing you need to stop this code using IS_ERR_VALUE() at all.

Those are two separate issues:

a) The ucc_geth driver mixing kmalloc() memory with muram, and assigning
   the result to "u32" and "void __iomem *" variables, both of which
   are wrong at least half of the time.

b) calling conventions of qe_muram_alloc() being defined in a way that
   requires the use of IS_ERR_VALUE(), because '0' is a valid address
   here.

Yep, it is all a big bag of worms...
'0' being valid is going to make tidying up after failure 'problematic'.

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The first one can be solved by updating the network driver, ideally
by getting rid of the casts and using proper types and accessors,
while the second would require updating all users of that interface.

It might be worth (at least as a compilation option) of embedding the
'muram offset' in a structure (passed and returned by value).

The compiler can then check that the driver code is never be looking
directly at the value.

For 'b' zero can be made invalid by changing the places where the
offset is added/subtracted.
It could even be used to offset the saved physical and virtual
addresses of the area - so not needing any extra code when the values
are converted to physical/virtual addresses.

Agreed.

For this driver, we don't actually seem to use the value returned from
the allocation function, only the virtual __iomem address we get after
calling qe_muram_addr(), so it would be a big improvement to just
store the virtual address as a pointer, and wrap the calls
to qe_muram_alloc/qe_muram_addr/qe_muram_free with an appropriate
helper that doesn't even show the offset.

However, I'd also separate the normal kmalloc pointer from the
muram_alloc() pointer because only the latter is __iomem, and
we shouldn't really call MMIO accessor functions on RAM in
portable code.

	Arnd