scs: fix a wrong parameter in __scs_magic

In the Linux kernel, the following vulnerability has been resolved:

scs: fix a wrong parameter in __scs_magic

__scs_magic() needs a 'void *' variable, but a 'struct task_struct *' is given. 'task_scs(tsk)' is the starting address of the task's shadow call stack, and '__scs_magic(task_scs(tsk))' is the end address of the task's shadow call stack. Here should be '__scs_magic(task_scs(tsk))'.

The user-visible effect of this bug is that when CONFIG_DEBUG_STACK_USAGE is enabled, the shadow call stack usage checking function (scs_check_usage) would scan an incorrect memory range. This could lead

1. Inaccurate stack usage reporting: The function would calculate wrong usage statistics for the shadow call stack, potentially showing incorrect value in kmsg.

2. Potential kernel crash: If the value of __scs_magic(tsk)is greater than that of __scs_magic(task_scs(tsk)), the for loop may access unmapped memory, potentially causing a kernel panic. However, this scenario is unlikely because task_struct is allocated via the slab allocator (which typically returns lower addresses), while the shadow call stack returned by task_scs(tsk) is allocated via vmalloc(which typically returns higher addresses).

However, since this is purely a debugging feature (CONFIG_DEBUG_STACK_USAGE), normal production systems should be not unaffected. The bug only impacts developers and testers who are actively debugging stack usage with this configuration enabled.