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SubjectRe: [PATCH v3 22/71] ARC: [Review] Prevent incorrect syscall restarts
Hi Al,

On Thursday 24 January 2013 04:20 PM, Vineet Gupta wrote:
> Per Al Viro's "signals for dummies" https://lkml.org/lkml/2012/12/6/366
> there are 3 golden rules for (not) restarting syscalls:
>
> " What we need to guarantee is
> * restarts do not happen on signals caught in interrupts or exceptions
> * restarts do not happen on signals caught in sigreturn()
> * restart should happen only once, even if we get through do_signal()
> many times."
>
> ARC Port already handled #1, this patch fixes #2 and #3.
>
> We use the additional state in pt_regs->orig_r8 to ckh if restarting
> has already been done once.
>
> Thanks to Al Viro for spotting this.
>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> Cc: Al Viro <viro@ZenIV.linux.org.uk>
> ---
> arch/arc/include/asm/ptrace.h | 3 +++
> arch/arc/kernel/signal.c | 12 ++++++++----
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
> index 1711d56..8bf7ff4 100644
> --- a/arch/arc/include/asm/ptrace.h
> +++ b/arch/arc/include/asm/ptrace.h
> @@ -135,6 +135,9 @@ struct user_regs_struct {
> #define in_syscall(regs) (regs->event & orig_r8_IS_SCALL)
> #define in_brkpt_trap(regs) (regs->event & orig_r8_IS_BRKPT)
>
> +#define syscall_wont_restart(regs) (regs->event |= orig_r8_IS_SCALL_RESTARTED)
> +#define syscall_restartable(regs) !(regs->event & orig_r8_IS_SCALL_RESTARTED)
> +
> #define current_pt_regs() \
> ({ \
> /* open-coded current_thread_info() */ \
> diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
> index 887a383..9a1ea2b 100644
> --- a/arch/arc/kernel/signal.c
> +++ b/arch/arc/kernel/signal.c
> @@ -131,6 +131,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
> if (restore_altstack(&sf->uc.uc_stack))
> goto badframe;
>
> + /* Don't restart from sigreturn */
> + syscall_wont_restart(regs);
> +
> return regs->r0;
>
> badframe:
> @@ -321,13 +324,13 @@ void do_signal(struct pt_regs *regs)
>
> signr = get_signal_to_deliver(&info, &ka, regs, NULL);
>
> - /* Are we from a system call? */
> - restart_scall = in_syscall(regs);
> + restart_scall = in_syscall(regs) && syscall_restartable(regs);
>
> if (signr > 0) {
> - if (restart_scall)
> + if (restart_scall) {
> arc_restart_syscall(&ka, regs);
> -
> + syscall_wont_restart(regs); /* No more restarts */
> + }
> handle_signal(signr, &ka, &info, regs);
> return;
> }
> @@ -342,6 +345,7 @@ void do_signal(struct pt_regs *regs)
> regs->r8 = __NR_restart_syscall;
> regs->ret -= 4;
> }
> + syscall_wont_restart(regs); /* No more restarts */
> }
>
> /* If there's no signal to deliver, restore the saved sigmask back */
>

If this looks OK, can I get your ACK on this.

Thx,
-Vineet


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