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s390/entry: add support for syscall stack randomization

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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: Sven Schnelle <svens@linux.ibm.com>
Link: https://lore.kernel.org/r/20210429091451.1062594-1-svens@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Sven Schnelle 2021-04-29 11:14:51 +02:00 committed by Heiko Carstens
parent f5b474deca
commit bae1cd368c
4 changed files with 14 additions and 0 deletions
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1
arch/s390/Kconfig
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@ -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

10
arch/s390/include/asm/entry-common.h
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@ -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));

1
arch/s390/kernel/syscall.c
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@ -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));

2
arch/s390/kernel/traps.c
View File

@ -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;