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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
