On 11/22/2017 01:15 PM, Florian Weimer wrote:

On 11/22/2017 09:18 AM, Vlastimil Babka wrote:

quoted

And, was the pkey == -1 internal wiring supposed to be exposed to the
pkey_mprotect() signal, or should there have been a pre-check returning
EINVAL in SYSCALL_DEFINE4(pkey_mprotect), before calling
do_mprotect_pkey())? I assume it's too late to change it now anyway (or
not?), so should we also document it?

I think the -1 case to the set the default key is useful because it 
allows you to use a key value of -1 to mean “MPK is not supported”, and 
still call pkey_mprotect.

Hmm the current manpage says then when MPK is not supported, pkey has to
be specified 0. Which is a value that doesn't work when MPK *is*
supported. So -1 is more universal indeed.

I plan to document this behavior on the glibc side, and glibc will call 
mprotect (not pkey_mprotect) for key -1, so that you won't get ENOSYS 
with kernels which do not support pkey_mprotect.

Fair enough. What will you do about pkey_alloc() in that case, emulate
ENOSPC? Oh, the manpage already suggests so. And the return value in
that case is... -1. Makes sense :)

Thanks,
Florian
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