Messages in this thread | | | Date | Fri, 12 Feb 2016 14:56:57 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v3 3/4] x86/signal/64: Re-add support for SS in the 64-bit signal context |
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On Thu, Feb 11, 2016 at 05:01:39PM -0800, Andy Lutomirski wrote: > On Thu, Feb 11, 2016 at 11:49 AM, Borislav Petkov <bp@alien8.de> wrote: > > On Mon, Jan 25, 2016 at 01:34:14PM -0800, Andy Lutomirski wrote: > > > >> + * with a flat 32-bit selector. > > How about: > > Sigreturn restores SS as follows: > > if (saved SS is valid || UC_STRICT_RESTORE_SS is set || saved CS is not 64-bit) > new SS = saved SS > else > new SS = a flat 32-bit data segment
Much better!
> How about: > > --- cut here --- > > This behavior serves three purposes: > > - Legacy programs that construct a 64-bit sigcontext from scratch > with zero or garbage in the SS slot (e.g. old CRIU) and call sigreturn > will still work. > > - Old DOSEMU versions sometimes catch a signal from a segmented > context, delete the old SS segment (with modify_ldt), and change the > saved CS to a 64-bit segment. These DOSEMU versions expect sigreturn > to send them back to 64-bit mode without killing them, despite the > fact that the SS selector when the signal was raised is no longer > valid. With UC_STRICT_RESTORE_SS clear, the kernel will fix up SS for > these DOSEMU versions.
... and with UC_STRICT_RESTORE_SS set, they'll get __USER_DS.
> - Old and new programs that catch a signal and return without > modifying the saved context will end up in exactly the state they > started in. Old kernels would lose track of the previous SS value. > > --- cut here ---
Yap, definitely better.
> FWIW, I have a DOSEMU patch that makes it use UC_STRICT_RESTORE_SS to > get the behavior it actually wants on new kernels. It should make it > faster and more reliable than was possible before.
Cool.
Thanks.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
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