Re: [RFC 1/3] x86/signal: add SA_{X32,IA32}_ABI sa_flags

From: Andy Lutomirski
Date: Mon Apr 25 2016 - 15:20:56 EST

On Mon, Apr 25, 2016 at 9:12 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
> Introduce new flags that defines which ABI to use on creating sigframe.
> Those flags one may set from the userspace, or kernel will set them
> according to syscall, which sets handler for a signal.
> So that will drop the dependency on TIF_IA32/TIF_X32 flags on syscall deliver.
> Those flags will be used only under CONFIG_COMPAT.
>
> The same way ARM uses sa_flags to differ in which mode deliver signal
> for 26-bit applications (look at SA_THIRYTWO).

Hmm. Do we want to make these user-visible at all, or should it be
purely an in-kernel thing?

--Andy

>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> ---
> arch/x86/ia32/ia32_signal.c | 2 +-
> arch/x86/include/asm/fpu/signal.h | 6 ++++++
> arch/x86/include/uapi/asm/signal.h | 6 +++++-
> arch/x86/kernel/signal.c | 19 ++++++++++---------
> arch/x86/kernel/signal_compat.c | 33 ++++++++++++++++++++++++++++++---
> kernel/signal.c | 5 +++++
> 6 files changed, 57 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
> index 0552884da18d..faf1871300cb 100644
> --- a/arch/x86/ia32/ia32_signal.c
> +++ b/arch/x86/ia32/ia32_signal.c
> @@ -378,7 +378,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
> put_user_ex(*((u64 *)&code), (u64 __user *)frame->retcode);
> } put_user_catch(err);
>
> - err |= copy_siginfo_to_user32(&frame->info, &ksig->info);
> + err |= __copy_siginfo_to_user32(&frame->info, &ksig->info, false);
> err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
> regs, set->sig[0]);
> err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
> diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h
> index 0e970d00dfcd..20a1fbf7fe4e 100644
> --- a/arch/x86/include/asm/fpu/signal.h
> +++ b/arch/x86/include/asm/fpu/signal.h
> @@ -19,6 +19,12 @@ int ia32_setup_frame(int sig, struct ksignal *ksig,
> # define ia32_setup_rt_frame __setup_rt_frame
> #endif
>
> +#ifdef CONFIG_COMPAT
> +int __copy_siginfo_to_user32(compat_siginfo_t __user *to,
> + const siginfo_t *from, bool x32_ABI);
> +#endif
> +
> +
> extern void convert_from_fxsr(struct user_i387_ia32_struct *env,
> struct task_struct *tsk);
> extern void convert_to_fxsr(struct task_struct *tsk,
> diff --git a/arch/x86/include/uapi/asm/signal.h b/arch/x86/include/uapi/asm/signal.h
> index 8264f47cf53e..9c663b6fc023 100644
> --- a/arch/x86/include/uapi/asm/signal.h
> +++ b/arch/x86/include/uapi/asm/signal.h
> @@ -70,6 +70,8 @@ typedef unsigned long sigset_t;
> * SA_RESETHAND clears the handler when the signal is delivered.
> * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
> * SA_NODEFER prevents the current signal from being masked in the handler.
> + * SA_IA32_ABI/SA_X32_ABI indicates ABI for a signal frame,
> + * if neither is set, the kernel will set them according to a syscall ABI
> *
> * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
> * Unix names RESETHAND and NODEFER respectively.
> @@ -85,7 +87,9 @@ typedef unsigned long sigset_t;
> #define SA_NOMASK SA_NODEFER
> #define SA_ONESHOT SA_RESETHAND
>
> -#define SA_RESTORER 0x04000000
> +#define SA_RESTORER 0x04000000u
> +#define SA_IA32_ABI 0x02000000u
> +#define SA_X32_ABI 0x01000000u
>
> #define MINSIGSTKSZ 2048
> #define SIGSTKSZ 8192
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index aa31265aa61d..8d13556f7df2 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -548,7 +548,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
> return -EFAULT;
>
> if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
> - if (copy_siginfo_to_user32(&frame->info, &ksig->info))
> + if (__copy_siginfo_to_user32(&frame->info, &ksig->info, true))
> return -EFAULT;
> }
>
> @@ -661,20 +661,21 @@ badframe:
> return 0;
> }
>
> -static inline int is_ia32_compat_frame(void)
> +static inline int is_ia32_compat_frame(struct ksignal *ksig)
> {
> return config_enabled(CONFIG_IA32_EMULATION) &&
> - test_thread_flag(TIF_IA32);
> + ksig->ka.sa.sa_flags & SA_IA32_ABI;
> }
>
> -static inline int is_ia32_frame(void)
> +static inline int is_ia32_frame(struct ksignal *ksig)
> {
> - return config_enabled(CONFIG_X86_32) || is_ia32_compat_frame();
> + return config_enabled(CONFIG_X86_32) || is_ia32_compat_frame(ksig);
> }
>
> -static inline int is_x32_frame(void)
> +static inline int is_x32_frame(struct ksignal *ksig)
> {
> - return config_enabled(CONFIG_X86_X32_ABI) && test_thread_flag(TIF_X32);
> + return config_enabled(CONFIG_X86_X32_ABI) &&
> + ksig->ka.sa.sa_flags & SA_X32_ABI;
> }
>
> static int
> @@ -685,12 +686,12 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
> compat_sigset_t *cset = (compat_sigset_t *) set;
>
> /* Set up the stack frame */
> - if (is_ia32_frame()) {
> + if (is_ia32_frame(ksig)) {
> if (ksig->ka.sa.sa_flags & SA_SIGINFO)
> return ia32_setup_rt_frame(usig, ksig, cset, regs);
> else
> return ia32_setup_frame(usig, ksig, cset, regs);
> - } else if (is_x32_frame()) {
> + } else if (is_x32_frame(ksig)) {
> return x32_setup_rt_frame(ksig, cset, regs);
> } else {
> return __setup_rt_frame(ksig->sig, ksig, set, regs);
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index dc3c0b1c816f..7f2d7c784a47 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -1,10 +1,31 @@
> #include <linux/compat.h>
> #include <linux/uaccess.h>
> +#include <linux/ptrace.h>
>
> -int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
> +void sigaction_compat_abi(struct k_sigaction *act)
> +{
> + if (!act)
> + return;
> +
> + /* don't let to set both ABI flags */
> + if (act->sa.sa_flags & SA_IA32_ABI && act->sa.sa_flags & SA_X32_ABI)
> + act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
> +
> + if (user_64bit_mode(current_pt_regs()))
> + return;
> +
> + if (!(act->sa.sa_flags & (SA_IA32_ABI | SA_X32_ABI))) {
> + if (in_ia32_syscall())
> + act->sa.sa_flags |= SA_IA32_ABI;
> + if (in_x32_syscall())
> + act->sa.sa_flags |= SA_X32_ABI;
> + }
> +}
> +
> +int __copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from,
> + bool x32_ABI)
> {
> int err = 0;
> - bool ia32 = test_thread_flag(TIF_IA32);
>
> if (!access_ok(VERIFY_WRITE, to, sizeof(compat_siginfo_t)))
> return -EFAULT;
> @@ -38,7 +59,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
> put_user_ex(from->si_arch, &to->si_arch);
> break;
> case __SI_CHLD >> 16:
> - if (ia32) {
> + if (!x32_ABI) {
> put_user_ex(from->si_utime, &to->si_utime);
> put_user_ex(from->si_stime, &to->si_stime);
> } else {
> @@ -72,6 +93,12 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
> return err;
> }
>
> +/* from syscall's path, where we know the ABI */
> +int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
> +{
> + return __copy_siginfo_to_user32(to, from, in_x32_syscall());
> +}
> +
> int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
> {
> int err = 0;
> diff --git a/kernel/signal.c b/kernel/signal.c
> index aa9bf00749c1..d0309f2a36f0 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -3048,6 +3048,10 @@ void kernel_sigaction(int sig, __sighandler_t action)
> }
> EXPORT_SYMBOL(kernel_sigaction);
>
> +void __weak sigaction_compat_abi(struct k_sigaction *act)
> +{
> +}
> +
> int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
> {
> struct task_struct *p = current, *t;
> @@ -3058,6 +3062,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
> return -EINVAL;
>
> k = &p->sighand->action[sig-1];
> + sigaction_compat_abi(act);
>
> spin_lock_irq(&p->sighand->siglock);
> if (oact)
> --
> 2.8.0
>



--
Andy Lutomirski
AMA Capital Management, LLC