Helge Deller [off-list ref] writes:

On 23.02.2018 01:15, Eric W. Biederman wrote:

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Helge Deller [off-list ref] writes:

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* Eric W. Biederman [off-list ref]:

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Setting si_code to 0 results in a userspace seeing an si_code of 0.
This is the same si_code as SI_USER.  Posix and common sense requires
that SI_USER not be a signal specific si_code.  As such this use of 0
for the si_code is a pretty horribly broken ABI.

Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
value of __SI_KILL and now sees a value of SIL_KILL with the result
that uid and pid fields are copied and which might copying the si_addr
field by accident but certainly not by design.  Making this a very
flakey implementation.

Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the
appropriate fields will reliably be copied.

This bug is 13 years old and parsic machines are no longer being built
so I don't know if it possible or worth fixing it.  But it is at least
worth documenting this so other architectures don't make the same
mistake.

I think we should fix it, even if we now break the ABI.

It's about a "conditional trap" which needs to be handled by userspace.
I doubt there is any Linux code out which is utilizing this
parisc-specific trap.

I'd suggest to add a new FPE trap si_code (e.g. FPE_CONDTRAP).
While at it, maybe we should include the already existing FPE_MDAOVF
from the frv architecture, so that arch/frv/include/uapi/asm/siginfo.h
can go completely.

Suggested patch is below.

I'm willing to test the patch below on the parisc architecture for a few
weeks. And it will break arch/x86/kernel/signal_compat.c which needs
looking at then too.

Have you managed to test this change?

Sadly I haven't done any further testing yet.

So at this point for purposed of testing I don't think it matters which
number FPE_CONDTRAP gets as long as it is non-zero.

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I am sitting looking at another new FPE si_code and if this has been tested
I figure FPE_CONDTRAP should get the next available FPE si_code and the
other change should get the one that follows.

I'm fine either way. Do you have a git tree I can pull which includes
all your patches? I can then start testing.

Everything finalized is in Linus's tree.  There is a patch pending
review on linux-arch that defines FPE_FLTUNK that looks to be useful
on several architectures.

I had probably misread our earlier exchange.  I had hoped you had tested
that FPE_CONDTRAP did not cause problems.

If that level of testing was complete I would have given FPE_CONDTRAP
the next FPE number and FPE_FLTUNK the one after.

As it sounds like FPE_CONDTRAP hasn't been tested enough to know if it
causes problems I will encourage the patches to be merged in the other
order.

Eric