commit 55516b355b0c cause SMEP/SMAP feature not work

[guocai he]

Andy, Thomas and all:

> branch: v5.15/standard/preempt-rt/x86
>
> commit: 55516b355b0c x86/syscall: Don't force use of indirect calls 
> for system calls
>
> I found this commit cause the intel CPU feature of SMEP/SMAP does not 
> work.
SMEP/SMAP is to "trick" the kernel into using instructions or data from 
a user-space program and get call trace
> testing:
>
> 1 enable SMEP/SMAP
>
> 2 in user-space, the test case source code:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
> #include <sys/mman.h>
> #include <sys/syscall.h>
> #include <errno.h>
>
> #define BUF_SIZE 128
>
> int main(int argc, char **argv)
> {
>     char *map;
>
>     map = mmap(NULL , 1024, PROT_READ|PROT_WRITE|PROT_EXEC, 
> MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
>     if (map == MAP_FAILED) {
>         printf("Failed to mmap: %s\n", strerror(errno));
>         return -1;
>     }
>
>     memset(map, 0, sizeof(BUF_SIZE));
>
>     mlockall(MCL_CURRENT);
>
>     syscall(247, map);
>
>     return 0;
> }

> 3 after the test case  executed, expect to get the call trace. but 
> this commit cause the test case can not find the call trace.
>
>
> do you have chance to look at this issue?
>
>
> Thanks
>
> Guocai