On Thu, 2017-05-18 at 10:37:31 UTC, Michael Ellerman wrote:
> virt_addr_valid() is supposed to tell you if it's OK to call virt_to_page() on
> an address. What this means in practice is that it should only return true for
> addresses in the linear mapping which are backed by a valid PFN.
>
> We are failing to properly check that the address is in the linear mapping,
> because virt_to_pfn() will return a valid looking PFN for more or less any
> address. That bug is actually caused by __pa(), used in virt_to_pfn().
>
> eg: __pa(0xc000000000010000) = 0x10000 # Good
> __pa(0xd000000000010000) = 0x10000 # Bad!
> __pa(0x0000000000010000) = 0x10000 # Bad!
>
> This started happening after commit bdbc29c19b26 ("powerpc: Work around gcc
> miscompilation of __pa() on 64-bit") (Aug 2013), where we changed the
> definition
> of __pa() to work around a GCC bug. Prior to that we subtracted PAGE_OFFSET
> from
> the value passed to __pa(), meaning __pa() of a 0xd or 0x0 address would give
> you something bogus back.
>
> Until we can verify if that GCC bug is no longer an issue, or come up with
> another solution, this commit does the minimal fix to make virt_addr_valid()
> work, by explicitly checking that the address is in the linear mapping region.
>
> Fixes: bdbc29c19b26 ("powerpc: Work around gcc miscompilation of __pa() on
> 64-bit")
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> Reviewed-by: Paul Mackerras <pau...@ozlabs.org>
> Reviewed-by: Balbir Singh <bsinghar...@gmail.com>
> Tested-by: Breno Leitao <breno.lei...@gmail.com>
Applied to powerpc fixes.
https://git.kernel.org/powerpc/c/e41e53cd4fe331d0d1f06f8e4ed7e2
cheers
