From: Chang S. Bae
> Sent: 22 April 2021 05:49
>
> The kernel pushes context on to the userspace stack to prepare for the
> user's signal handler. When the user has supplied an alternate signal
> stack, via sigaltstack(2), it is easy for the kernel to verify that the
> stack size is sufficient for the current hardware context.
>
> Check if writing the hardware context to the alternate stack will exceed
> it's size. If yes, then instead of corrupting user-data and proceeding with
> the original signal handler, an immediate SIGSEGV signal is delivered.
What happens if SIGSEGV is caught?
> Refactor the stack pointer check code from on_sig_stack() and use the new
> helper.
>
> While the kernel allows new source code to discover and use a sufficient
> alternate signal stack size, this check is still necessary to protect
> binaries with insufficient alternate signal stack size from data
> corruption.
...
> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> index 3f6a0fcaa10c..ae60f838ebb9 100644
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -537,6 +537,17 @@ static inline int kill_cad_pid(int sig, int priv)
> #define SEND_SIG_NOINFO ((struct kernel_siginfo *) 0)
> #define SEND_SIG_PRIV ((struct kernel_siginfo *) 1)
>
> +static inline int __on_sig_stack(unsigned long sp)
> +{
> +#ifdef CONFIG_STACK_GROWSUP
> + return sp >= current->sas_ss_sp &&
> + sp - current->sas_ss_sp < current->sas_ss_size;
> +#else
> + return sp > current->sas_ss_sp &&
> + sp - current->sas_ss_sp <= current->sas_ss_size;
> +#endif
> +}
> +
Those don't look different enough.
David
-
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