[PATCH] signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die

Finn Thain
2024-09-27T03:45:10Z

From: Eric W. Biederman <ebiederm@xmission.com>

[ Upstream commit a3616a3c02722d1edb95acc7fceade242f6553ba ]

In the fpsp040 code when copyin or copyout fails call
force_sigsegv(SIGSEGV) instead of do_exit(SIGSEGV).

This solves a couple of problems. Because do_exit embeds the ptrace
stop PTRACE_EVENT_EXIT a complete stack frame needs to be present for
that to work correctly. There is always the information needed for a
ptrace stop where get_signal is called. So exiting with a signal
solves the ptrace issue.

Further exiting with a signal ensures that all of the threads in a
process are killed not just the thread that malfunctioned. Which
avoids confusing userspace.

To make force_sigsegv(SIGSEGV) work in fpsp040_die modify the code to
save all of the registers and jump to ret_from_exception (which
ultimately calls get_signal) after fpsp040_die returns.

v2: Updated the branches to use gas's pseudo ops that automatically
calculate the best branch instruction to use for the purpose.

Cc: stable@kernel.org # <= 5.14.y
v1: https://lkml.kernel.org/r/87a6m8kgtx.fsf_-_@disp2133
Link: https://lkml.kernel.org/r/87tukghjfs.fsf_-_@disp2133
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
arch/m68k/fpsp040/skeleton.S | 3 ++-
arch/m68k/kernel/traps.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/fpsp040/skeleton.S b/arch/m68k/fpsp040/skeleton.S
index 31a9c634c81e..081922c72daa 100644
--- a/arch/m68k/fpsp040/skeleton.S
+++ b/arch/m68k/fpsp040/skeleton.S
@@ -502,7 +502,8 @@ in_ea:
.section .fixup,"ax"
.even
1:
- jbra fpsp040_die
+ jbsr fpsp040_die
+ jbra .Lnotkern

.section __ex_table,"a"
.align 4
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 35f706d836c5..c6f18dc5884b 100644
--- a/arch/m68k/kernel/traps.c
+++ b/arch/m68k/kernel/traps.c
@@ -1155,7 +1155,7 @@ asmlinkage void set_esp0(unsigned long ssp)
*/
asmlinkage void fpsp040_die(void)
{
- do_exit(SIGSEGV);
+ force_sigsegv(SIGSEGV, current);
}

#ifdef CONFIG_M68KFPU_EMU
--
2.39.5