Commit bae1cd36 authored by Sven Schnelle's avatar Sven Schnelle Committed by Heiko Carstens
Browse files

s390/entry: add support for syscall stack randomization 



This adds support for adding a random offset to the stack while handling
syscalls. The patch uses get_tod_clock_fast() as this is considered good
enough and has much less performance penalty compared to using
get_random_int(). The patch also adds randomization in pgm_check_handler()
as the sigreturn/rt_sigreturn system calls might be called from there.

Signed-off-by: default avatarSven Schnelle <svens@linux.ibm.com>
Link: https://lore.kernel.org/r/20210429091451.1062594-1-svens@linux.ibm.com


Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent f5b474de

arch/s390/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -137,6 +137,7 @@ config S390 
	select HAVE_ARCH_JUMP_LABEL_RELATIVE

	select HAVE_ARCH_KASAN

	select HAVE_ARCH_KASAN_VMALLOC

	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET

	select HAVE_ARCH_SECCOMP_FILTER

	select HAVE_ARCH_SOFT_DIRTY

	select HAVE_ARCH_TRACEHOOK

arch/s390/include/asm/entry-common.h

+10 −0
Original line number Diff line number Diff line
@@ -4,9 +4,11 @@ 


#include <linux/sched.h>

#include <linux/audit.h>

#include <linux/randomize_kstack.h>

#include <linux/tracehook.h>

#include <linux/processor.h>

#include <linux/uaccess.h>

#include <asm/timex.h>

#include <asm/fpu/api.h>



#define ARCH_EXIT_TO_USER_MODE_WORK (_TIF_GUARDED_STORAGE | _TIF_PER_TRAP)
@@ -48,6 +50,14 @@ static __always_inline void arch_exit_to_user_mode(void) 


#define arch_exit_to_user_mode arch_exit_to_user_mode



static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,

						  unsigned long ti_work)

{

	choose_random_kstack_offset(get_tod_clock_fast() & 0xff);

}



#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare



static inline bool on_thread_stack(void)

{

	return !(((unsigned long)(current->stack) ^ current_stack_pointer()) & ~(THREAD_SIZE - 1));

arch/s390/kernel/syscall.c

+1 −0
Original line number Diff line number Diff line
@@ -142,6 +142,7 @@ void do_syscall(struct pt_regs *regs) 


void noinstr __do_syscall(struct pt_regs *regs, int per_trap)

{

	add_random_kstack_offset();

	enter_from_user_mode(regs);



	memcpy(&regs->gprs[8], S390_lowcore.save_area_sync, 8 * sizeof(unsigned long));

arch/s390/kernel/traps.c

+2 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include "asm/ptrace.h"

#include <linux/kprobes.h>

#include <linux/kdebug.h>

#include <linux/randomize_kstack.h>

#include <linux/extable.h>

#include <linux/ptrace.h>

#include <linux/sched.h>
@@ -301,6 +302,7 @@ void noinstr __do_pgm_check(struct pt_regs *regs) 
	unsigned int trapnr, syscall_redirect = 0;

	irqentry_state_t state;



	add_random_kstack_offset();

	regs->int_code = *(u32 *)&S390_lowcore.pgm_ilc;

	regs->int_parm_long = S390_lowcore.trans_exc_code;