Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

[Linus Torvalds]

On Fri, Dec 18, 2015 at 12:07 PM, Dave Hansen
<dave.hansen@xxxxxxxxxxxxxxx> wrote:
>
> But, I think it's a small one.  Basically, RSP would have to pointing at
> a place which was allowed by protection keys for all of the sigframe
> setup.

Note that the whole "stack is special" is not at all a new issue.

It's the main reason why sigaltstack() and SS_ONSTACK exists. This is
in no way new to PKRU, people have had to handle the issue of
stack-related SIGSEGV faults for a long time.

So any application that uses PKRU and may play games that affects the
stack, will always have to have a separate "safe stack" that it uses
for signal handling. But that is in no way PKRU-specific, it's been
the case for a lot of other memory management faults.

                  Linus
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