[PATCH v1] m68k: save extra registers on sys_exit and sys_exit_group syscall entry

Michael Schmitz
2021-06-12T23:39:33Z

do_exit() calls prace_stop() which may require access to all saved
registers. We only save those registers not preserved by C code
currently.

Provide a special syscall entry for exit and exit_group syscalls
similar to that used by clone and clone3, which have the same
requirements.

No fix to io_uring appears to be needed, because m68k copy_thread
treats kernel threads the same as e.g. alpha does, and copies only
a subset of registers in that case.

CC: Eric W. Biederman <ebiederm@xmission.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---
arch/m68k/kernel/entry.S | 14 ++++++++++++++
arch/m68k/kernel/process.c | 16 ++++++++++++++++
arch/m68k/kernel/syscalls/syscall.tbl | 4 ++--
3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 9dd76fb..1e067e6 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -76,6 +76,20 @@ ENTRY(__sys_clone3)
lea %sp@(28),%sp
rts

+ENTRY(__sys_exit)
+ SAVE_SWITCH_STACK
+ pea %sp@(SWITCH_STACK_SIZE)
+ jbsr m68k_exit
+ lea %sp@(28),%sp
+ rts
+
+ENTRY(__sys_exit_group)
+ SAVE_SWITCH_STACK
+ pea %sp@(SWITCH_STACK_SIZE)
+ jbsr m68k_exit_group
+ lea %sp@(28),%sp
+ rts
+
ENTRY(sys_sigreturn)
SAVE_SWITCH_STACK
movel %sp,%sp@- | switch_stack pointer
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index da83cc8..df4e5f1 100644
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -138,6 +138,22 @@ asmlinkage int m68k_clone3(struct pt_regs *regs)
return sys_clone3((struct clone_args __user *)regs->d1, regs->d2);
}

+/*
+ * Because extra registers are saved on the stack after the sys_exit()
+ * arguments, this C wrapper extracts them from pt_regs * and then calls the
+ * generic sys_exit() implementation.
+ */
+asmlinkage int m68k_exit(struct pt_regs *regs)
+{
+ return sys_exit(regs->d1);
+}
+
+/* Same for sys_exit_group ... */
+asmlinkage int m68k_exit_group(struct pt_regs *regs)
+{
+ return sys_exit_group(regs->d1);
+}
+
int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
struct task_struct *p, unsigned long tls)
{
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 0dd019d..3d5b6fbc 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -8,7 +8,7 @@
# The <abi> is always "common" for this file
#
0 common restart_syscall sys_restart_syscall
-1 common exit sys_exit
+1 common exit __sys_exit
2 common fork __sys_fork
3 common read sys_read
4 common write sys_write
@@ -254,7 +254,7 @@
244 common io_submit sys_io_submit
245 common io_cancel sys_io_cancel
246 common fadvise64 sys_fadvise64
-247 common exit_group sys_exit_group
+247 common exit_group __sys_exit_group
248 common lookup_dcookie sys_lookup_dcookie
249 common epoll_create sys_epoll_create
250 common epoll_ctl sys_epoll_ctl
--
2.7.4