[PATCH] riscv: entry: Fixup do_trap_break from kernel side

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

The irqentry_nmi_enter/exit would force the current context into in_interrupt.
That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to
debug the kernel.

Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break
of the kernel side.

Before the fixup:
$echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
  lkdtm: Performing direct entry BUG
  ------------[ cut here ]------------
  kernel BUG at drivers/misc/lkdtm/bugs.c:78!
  handle_break, 256.
  Kernel BUG [#1]
  Modules linked in:
  CPU: 0 PID: 104 Comm: echo Not tainted 6.4.0-rc1-00055-g0ca05a4b079f-dirty #30
  Hardware name: riscv-virtio,qemu (DT)
  epc : lkdtm_BUG+0x6/0x8
   ra : lkdtm_do_action+0x14/0x1c
  epc : ffffffff8055c730 ra : ffffffff8087e188 sp : ff200000007dbd40
   gp : ffffffff81500878 tp : ff600000028ebac0 t0 : 6500000000000000
   t1 : 000000000000006c t2 : 6550203a6d74646b s0 : ff200000007dbd50
   s1 : ffffffff814bfc80 a0 : ffffffff814bfc80 a1 : ff6000001ffd8608
   a2 : ff6000001ffdb870 a3 : 0000000000000000 a4 : 0000000000000000
   a5 : ffffffff8055c72a a6 : 0000000000000032 a7 : 0000000000000038
   s2 : 0000000000000004 s3 : 00000000556371a0 s4 : ff200000007dbe70
   s5 : ff60000002090000 s6 : 00000000556371a0 s7 : 0000000000000030
   s8 : 000000007fffec78 s9 : 0000000000000007 s10: 0000000055637530
   s11: 0000000000000001 t3 : ffffffff81513ed7 t4 : ffffffff81513ed7
   t5 : ffffffff81513ed8 t6 : ff200000007dbb88
  status: 0000000100000120 badaddr: 0000000000000000 cause: 0000000000000003
  [<ffffffff8055c730>] lkdtm_BUG+0x6/0x8
  Code: 0513 6b05 b097 0031 80e7 e960 b705 1141 e422 0800 (9002) 1141
  ---[ end trace 0000000000000000 ]---
  Kernel panic - not syncing: Aiee, killing interrupt handler!
  ---[ end Kernel panic - not syncing: Aiee, killing interrupt handler! ]---

(Dead in the kernel side.)

After the fixup:
$echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
  lkdtm: Performing direct entry BUG
  ------------[ cut here ]------------
  kernel BUG at drivers/misc/lkdtm/bugs.c:78!
  Kernel BUG [#13]
  Modules linked in:
  CPU: 0 PID: 129 Comm: echo Tainted: G D 6.4.0-rc1-00055-g0ca05a4b079f-dirty #34
  Hardware name: riscv-virtio,qemu (DT)
  epc : lkdtm_BUG+0x6/0x8
   ra : lkdtm_do_action+0x14/0x1c
  epc : ffffffff8055c71c ra : ffffffff8087e170 sp : ff200000007e3d40
   gp : ffffffff81500878 tp : ff600000028ebac0 t0 : 6500000000000000
   t1 : 000000000000006c t2 : 6550203a6d74646b s0 : ff200000007e3d50
   s1 : ffffffff814bfc80 a0 : ffffffff814bfc80 a1 : ff6000001ffd8608
   a2 : ff6000001ffdb870 a3 : 0000000000000000 a4 : 0000000000000000
   a5 : ffffffff8055c716 a6 : 0000000000000032 a7 : 0000000000000038
   s2 : 0000000000000004 s3 : 00000000556371a0 s4 : ff200000007e3e70
   s5 : ff60000002090000 s6 : 00000000556371a0 s7 : 0000000000000030
   s8 : 000000007fffec78 s9 : 0000000000000007 s10: 0000000055637530
   s11: 0000000000000001 t3 : ffffffff81513ed7 t4 : ffffffff81513ed7
   t5 : ffffffff81513ed8 t6 : ff200000007e3b88
  status: 0000000100000120 badaddr: 0000000000000000 cause: 0000000000000003
  [<ffffffff8055c71c>] lkdtm_BUG+0x6/0x8
  Code: 0513 6945 b097 0031 80e7 e920 b705 1141 e422 0800 (9002) 1141
  ---[ end trace 0000000000000000 ]---
  note: echo[129] exited with irqs disabled
  Segmentation fault

(Resume to the shell normally.)

Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reported-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/riscv/kernel/traps.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index efc6b649985a..ed0eb9452f9e 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -18,6 +18,7 @@
 #include <linux/irq.h>
 #include <linux/kexec.h>
 #include <linux/entry-common.h>
+#include <linux/context_tracking.h>
 
 #include <asm/asm-prototypes.h>
 #include <asm/bug.h>
@@ -257,11 +258,11 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
 
 		irqentry_exit_to_user_mode(regs);
 	} else {
-		irqentry_state_t state = irqentry_nmi_enter(regs);
+		enum ctx_state prev_state = exception_enter();
 
 		handle_break(regs);
 
-		irqentry_nmi_exit(regs, state);
+		exception_exit(prev_state);
 	}
 }
 
-- 
2.36.1