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Revert x86 sigcontext cleanups 

This reverts commits 9a036b93a3 ("x86/signal/64: Remove 'fs' and 'gs'
from sigcontext") and c6f2062935 ("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: Stas Sergeev <stsp@list.ru>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2015-08-13 08:25:20 -07:00
parent 26b552e0a8
commit ed596cde94
3 changed files with 17 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/include/asm/sigcontext.h
View File

@ -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;

21
arch/x86/include/uapi/asm/sigcontext.h
View File

@ -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;

26
arch/x86/kernel/signal.c
View File

@ -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;
}