Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 9 Mar 2015 13:15:33 -0700 | Subject | Re: [PATCH 1/2] x86_64,signal: Save and restore SS in signal frames |
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Hi Ingo,
Here's a blast from the past. I asked Andi today, and he seems conceptually okay with this. Could you consider applying it? Aside from being a bug fix IMO, it will allow my sigreturn test to work reasonably well as a native 64-bit program.
I checked: it still applies cleanly.
--Andy
On Fri, Jul 11, 2014 at 9:29 AM, Andy Lutomirski <luto@amacapital.net> wrote: > The comment in the signal code says that apps can save/restore other > segments on their own. It's true that apps can *save* SS on their > own, but there's no way for apps to restore it: SYSCALL effectively > resets SS to __USER_DS, so any value that user code tries to load > into SS gets lost on entry to sigreturn. > > This recycles two padding bytes in the segment selector area for SS. > > I suspect that 64-bit programs that try to run 16-bit code and uses > signals will have a lot of trouble without this. > > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > --- > arch/x86/include/asm/sigcontext.h | 2 +- > arch/x86/include/uapi/asm/sigcontext.h | 2 +- > arch/x86/kernel/signal.c | 8 +------- > 3 files changed, 3 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/include/asm/sigcontext.h b/arch/x86/include/asm/sigcontext.h > index 9dfce4e..f910cdc 100644 > --- a/arch/x86/include/asm/sigcontext.h > +++ b/arch/x86/include/asm/sigcontext.h > @@ -59,7 +59,7 @@ struct sigcontext { > unsigned short cs; > unsigned short gs; > unsigned short fs; > - unsigned short __pad0; > + unsigned short ss; > unsigned long err; > unsigned long trapno; > unsigned long oldmask; > diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h > index d8b9f90..076b11f 100644 > --- a/arch/x86/include/uapi/asm/sigcontext.h > +++ b/arch/x86/include/uapi/asm/sigcontext.h > @@ -179,7 +179,7 @@ struct sigcontext { > __u16 cs; > __u16 gs; > __u16 fs; > - __u16 __pad0; > + __u16 ss; > __u64 err; > __u64 trapno; > __u64 oldmask; > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > index 2851d63..08d7a9e 100644 > --- a/arch/x86/kernel/signal.c > +++ b/arch/x86/kernel/signal.c > @@ -94,15 +94,8 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, > COPY(r15); > #endif /* CONFIG_X86_64 */ > > -#ifdef CONFIG_X86_32 > COPY_SEG_CPL3(cs); > COPY_SEG_CPL3(ss); > -#else /* !CONFIG_X86_32 */ > - /* Kernel saves and restores only the CS segment register on signals, > - * which is the bare minimum needed to allow mixed 32/64-bit code. > - * App's signal handler can save/restore other segments if needed. */ > - COPY_SEG_CPL3(cs); > -#endif /* CONFIG_X86_32 */ > > get_user_ex(tmpflags, &sc->flags); > regs->flags = (regs->flags & ~FIX_EFLAGS) | (tmpflags & FIX_EFLAGS); > @@ -164,6 +157,7 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate, > put_user_ex(regs->cs, &sc->cs); > put_user_ex(0, &sc->gs); > put_user_ex(0, &sc->fs); > + put_user_ex(regs->ss, &sc->ss); > #endif /* CONFIG_X86_32 */ > > put_user_ex(fpstate, &sc->fpstate); > -- > 1.9.3 >
-- Andy Lutomirski AMA Capital Management, LLC
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