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SubjectRe: [PATCH 04/11] signal/parisc: Document a conflict with SI_USER with SIGFPE
On 23.02.2018 01:15, Eric W. Biederman wrote:
> Helge Deller <> writes:
>> * Eric W. Biederman <>:
>>> 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.

> 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.


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