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Commit ed596cde authored by Linus Torvalds's avatar Linus Torvalds
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Revert x86 sigcontext cleanups 



This reverts commits 9a036b93 ("x86/signal/64: Remove 'fs' and 'gs'
from sigcontext") and c6f20629 ("x86/signal/64: Fix SS handling for
signals delivered to 64-bit programs").

They were cleanups, but they break dosemu by changing the signal return
behavior (and removing 'fs' and 'gs' from the sigcontext struct - while
not actually changing any behavior - causes build problems).

Reported-and-tested-by: default avatarStas Sergeev <stsp@list.ru>
Acked-by: default avatarAndy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 26b552e0

arch/x86/include/asm/sigcontext.h

+3 −3
Original line number Diff line number Diff line
@@ -57,9 +57,9 @@ struct sigcontext { 
	unsigned long ip;

	unsigned long flags;

	unsigned short cs;

	unsigned short __pad2;	/* Was called gs, but was always zero. */

	unsigned short __pad1;	/* Was called fs, but was always zero. */

	unsigned short ss;

	unsigned short gs;

	unsigned short fs;

	unsigned short __pad0;

	unsigned long err;

	unsigned long trapno;

	unsigned long oldmask;

arch/x86/include/uapi/asm/sigcontext.h

+3 −18
Original line number Diff line number Diff line
@@ -177,24 +177,9 @@ struct sigcontext { 
	__u64 rip;

	__u64 eflags;		/* RFLAGS */

	__u16 cs;



	/*

	 * Prior to 2.5.64 ("[PATCH] x86-64 updates for 2.5.64-bk3"),

	 * Linux saved and restored fs and gs in these slots.  This

	 * was counterproductive, as fsbase and gsbase were never

	 * saved, so arch_prctl was presumably unreliable.

	 *

	 * If these slots are ever needed for any other purpose, there

	 * is some risk that very old 64-bit binaries could get

	 * confused.  I doubt that many such binaries still work,

	 * though, since the same patch in 2.5.64 also removed the

	 * 64-bit set_thread_area syscall, so it appears that there is

	 * no TLS API that works in both pre- and post-2.5.64 kernels.

	 */

	__u16 __pad2;		/* Was gs. */

	__u16 __pad1;		/* Was fs. */



	__u16 ss;

	__u16 gs;

	__u16 fs;

	__u16 __pad0;

	__u64 err;

	__u64 trapno;

	__u64 oldmask;

arch/x86/kernel/signal.c

+11 −15
Original line number Diff line number Diff line
@@ -93,8 +93,15 @@ 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);
@@ -154,9 +161,8 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate, 
#else /* !CONFIG_X86_32 */

		put_user_ex(regs->flags, &sc->flags);

		put_user_ex(regs->cs, &sc->cs);

		put_user_ex(0, &sc->__pad2);

		put_user_ex(0, &sc->__pad1);

		put_user_ex(regs->ss, &sc->ss);

		put_user_ex(0, &sc->gs);

		put_user_ex(0, &sc->fs);

#endif /* CONFIG_X86_32 */



		put_user_ex(fpstate, &sc->fpstate);
@@ -451,19 +457,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig, 


	regs->sp = (unsigned long)frame;



	/*

	 * Set up the CS and SS registers to run signal handlers in

	 * 64-bit mode, even if the handler happens to be interrupting

	 * 32-bit or 16-bit code.

	 *

	 * SS is subtle.  In 64-bit mode, we don't need any particular

	 * SS descriptor, but we do need SS to be valid.  It's possible

	 * that the old SS is entirely bogus -- this can happen if the

	 * signal we're trying to deliver is #GP or #SS caused by a bad

	 * SS value.

	 */

	/* Set up the CS register to run signal handlers in 64-bit mode,

	   even if the handler happens to be interrupting 32-bit code. */

	regs->cs = __USER_CS;

	regs->ss = __USER_DS;



	return 0;

}