Up
On Wed, Feb 01, 2017 at 09:43:57PM +0100, Laurent Vivier wrote:
> Le 31/01/2017 à 23:05, Jose Ricardo Ziviani a écrit :
> > A segfault is noticed when an emulated program uses any of ucontext
> > regs fields. Risu detected this issue in the following operation when
> > handling a signal:
> > ucontext_t *uc = (ucontext_t*)uc;
> > uc->uc_mcontext.regs->nip += 4;
> >
> > but this works fine:
> > uc->uc_mcontext.gp_regs[PT_NIP] += 4;
> >
> > This patch set regs to a valid location as well as other sigcontext
> > fields.
> >
> > Signed-off-by: Jose Ricardo Ziviani <jos...@linux.vnet.ibm.com>
> > ---
> > linux-user/signal.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/linux-user/signal.c b/linux-user/signal.c
> > index 5064de0..8209539 100644
> > --- a/linux-user/signal.c
> > +++ b/linux-user/signal.c
> > @@ -5155,6 +5155,7 @@ static void setup_rt_frame(int sig, struct
> > target_sigaction *ka,
> > target_ulong rt_sf_addr, newsp = 0;
> > int i, err = 0;
> > #if defined(TARGET_PPC64)
> > + struct target_sigcontext *sc = 0;
> > struct image_info *image = ((TaskState *)thread_cpu->opaque)->info;
> > #endif
> >
> > @@ -5183,6 +5184,10 @@ static void setup_rt_frame(int sig, struct
> > target_sigaction *ka,
> > #if defined(TARGET_PPC64)
> > mctx = &rt_sf->uc.tuc_sigcontext.mcontext;
> > trampptr = &rt_sf->trampoline[0];
> > +
> > + sc = &rt_sf->uc.tuc_sigcontext;
> > + __put_user(h2g(mctx), &sc->regs);
> > + __put_user(sig, &sc->signal);
> > #else
> > mctx = &rt_sf->uc.tuc_mcontext;
> > trampptr = (uint32_t *)&rt_sf->uc.tuc_mcontext.tramp;
> >
>
> Reviewed-by: Laurent Vivier <laur...@vivier.eu>
>
> This is correct, but QEMU and kernel implementation are really different.
>
> In the kernel:
>
> handle_rt_signal64()
> ...
> frame = get_sigframe(ksig, get_tm_stackpointer(tsk),
> sizeof(*frame), 0);
> ...
> err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
> NULL,
> (unsigned long)ksig->ka.sa.sa_handler,
> 1);
>
> static long setup_sigcontext(struct sigcontext __user *sc,
> struct task_struct *tsk, int signr, sigset_t *set,
> unsigned long handler, int ctx_has_vsx_region)
>
> err |= __put_user(&sc->gp_regs, &sc->regs);
> ...
> err |= __put_user(signr, &sc->signal);
> ...
>
> According to kernel definition of ucontext:
>
> struct ucontext {
> ...
> #ifdef __powerpc64__
> sigset_t __unused[15]; /* Allow for uc_sigmask growth */
> struct sigcontext uc_mcontext; /* last for extensibility */
> #else
> ...
> }
>
> kernel &frame->uc.uc_mcontext is qemu &rt_sf->uc.tuc_sigcontext
>
> uc_sigcontext.mcontext doesn't exit in the kernel.
>
> But QEMU code works because tuc_sigcontext.mcontext is where we have the
> CPU registers in sigcontext:
>
> kernel:
>
> struct sigcontext {
> unsigned long _unused[4];
> int signal;
> #ifdef __powerpc64__
> int _pad0;
> #endif
> unsigned long handler;
> unsigned long oldmask;
> struct pt_regs __user *regs;
> #ifdef __powerpc64__
> elf_gregset_t gp_regs;
> elf_fpregset_t fp_regs;
> ...
>
> Qemu:
>
> struct target_sigcontext {
> target_ulong _unused[4];
> int32_t signal;
> #if defined(TARGET_PPC64)
> int32_t pad0;
> #endif
> target_ulong handler;
> target_ulong oldmask;
> target_ulong regs; /* struct pt_regs __user * */
> #if defined(TARGET_PPC64)
> struct target_mcontext mcontext;
> #endif
> };
>
> struct target_mcontext {
> target_ulong mc_gregs[48];
> /* Includes fpscr. */
> uint64_t mc_fregs[33];
> ...
>
> I think we do like that to use the same
> save_user_regs()/save_user_regs() functions with PPC and PPC64... but
> comparison with kernel becomes harder.
>
> Laurent
>
