Re: [RFC] de-asmify the x86-64 system call slowpath

[Al Viro]

On Mon, Jan 27, 2014 at 02:17:23PM -0800, Linus Torvalds wrote:
> On Mon, Jan 27, 2014 at 2:06 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> >
> > It's not just ip and sp -- cs matters here, too, I think.
> 
> For signal *delivery*, CS will always be __USER_CS, and %rcx can be
> crap, so sysret should be fine. We could easily check that %rip is
> valid in the whole slow-path instead of saying "return 1 if we did
> do_signal()".

do_signal() is also a place where arbitrary changes to regs might've
been done by tracer, so regs->cs might need to be checked in the same
place where we validate regs->rip ;-/
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