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SubjectRe: Question on "uaccess: Add strict non-pagefault kernel-space read function"
On 4/7/20 11:33 AM, Christoph Hellwig wrote:
> On Tue, Apr 07, 2020 at 11:03:23AM +0200, Daniel Borkmann wrote:
>> ... where archs with non-overlapping user and kernel address range would
>> only end up having to implementing kernel_range_ok() check. Or, instead of
>> a generic kernel_range_ok() this could perhaps be more probing-specific as
>> in probe_kernel_range_ok() where this would then also cover the special
>> cases we seem to have in parisc and um. Then, this would allow to get rid
>> of all the __weak aliasing as well which may just be confusing. I could look
>> into coming up with something along these lines. Thoughts?
> FYI, this is what I cooked up a few days ago:
> Still misses the final work to switch probe_kernel_read to be the
> strict version. Any good naming suggestion for the non-strict one?

Ah great, thanks for working on it including the cleanups in your branch above.
Good naming suggestion is usually the hardest ... ;-) Maybe adding an _unsafe or
_lax suffix ...

Regarding commits:


reads a bit odd. Could we simply have an equivalent for access_ok() that archs
implement under KERNEL_DS where it covers the allowed/restricted kernel-only range?
Like mentioned earlier e.g. probe_{user,kernel}_range_ok() helpers where the user
one defaults to access_ok() internally and the kernel one contains all the range
restrictions that archs can then define if needed (and if not there could be an
asm-generic `return true` fallback, for example).


This would still need to set dst[0] = '\0' in that case to be consistent with
the other error handling cases there when count > 0.


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