Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs
From: Oleg Nesterov
Date: Wed Mar 18 2015 - 14:27:24 EST
On 03/18, Cyrill Gorcunov wrote:
>
> On Wed, Mar 18, 2015 at 11:06:00AM -0700, Andy Lutomirski wrote:
> > > --- a/arch/x86/crtools.c
> > > +++ b/arch/x86/crtools.c
> > > @@ -475,6 +475,7 @@ int restore_gpregs(struct rt_sigframe *f, UserX86RegsEntry *r)
> > > CPREG2(rip, ip);
> > > CPREG2(eflags, flags);
> > > CPREG1(cs);
> > > + CPREG1(ss);
> > > CPREG1(gs);
> > > CPREG1(fs);
> >
> > Huh? Is CRIU actually trying to build an entire sigcontext from
> > scratch here? I don't see how this can reliably work across kernel
> > versions or CPU versions.
>
> Yes we are. And why it can't work reliably? As to CPU -- we're
> testing that cpu features saved in image should match ones
> provided by the kernel runtime, ie on the machine where we're
> restoring.
But, say, __USER_CS can be changed in kernel, and nobody should notice this.
But in this case "restore on another machine" or "restore after kernel
upgrade" can fail.
So probably restore_gpregs() should only change the general-purpose regs,
as its name suggests.
Oleg.
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