This is a note to let you know that I've just added the patch titled
arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-kgdb-set-pstate.ss-to-1-to-re-enable-single-st.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4d59e512fe465fc97628b2019e3f503e33649f01
Author: Sumit Garg <sumit.garg@xxxxxxxxxx>
Date: Thu Feb 2 13:01:48 2023 +0530
arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step
[ Upstream commit af6c0bd59f4f3ad5daad2f7b777954b1954551d5 ]
Currently only the first attempt to single-step has any effect. After
that all further stepping remains "stuck" at the same program counter
value.
Refer to the ARM Architecture Reference Manual (ARM DDI 0487E.a) D2.12,
PSTATE.SS=1 should be set at each step before transferring the PE to the
'Active-not-pending' state. The problem here is PSTATE.SS=1 is not set
since the second single-step.
After the first single-step, the PE transferes to the 'Inactive' state,
with PSTATE.SS=0 and MDSCR.SS=1, thus PSTATE.SS won't be set to 1 due to
kernel_active_single_step()=true. Then the PE transferes to the
'Active-pending' state when ERET and returns to the debugger by step
exception.
Before this patch:
==================
Entering kdb (current=0xffff3376039f0000, pid 1) on processor 0 due to Keyboard Entry
[0]kdb>
[0]kdb>
[0]kdb> bp write_sysrq_trigger
Instruction(i) BP #0 at 0xffffa45c13d09290 (write_sysrq_trigger)
is enabled addr at ffffa45c13d09290, hardtype=0 installed=0
[0]kdb> go
$ echo h > /proc/sysrq-trigger
Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to Breakpoint @ 0xffffad651a309290
[1]kdb> ss
Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294
[1]kdb> ss
Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294
[1]kdb>
After this patch:
=================
Entering kdb (current=0xffff6851c39f0000, pid 1) on processor 0 due to Keyboard Entry
[0]kdb> bp write_sysrq_trigger
Instruction(i) BP #0 at 0xffffc02d2dd09290 (write_sysrq_trigger)
is enabled addr at ffffc02d2dd09290, hardtype=0 installed=0
[0]kdb> go
$ echo h > /proc/sysrq-trigger
Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to Breakpoint @ 0xffffc02d2dd09290
[1]kdb> ss
Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09294
[1]kdb> ss
Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09298
[1]kdb> ss
Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd0929c
[1]kdb>
Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support")
Co-developed-by: Wei Li <liwei391@xxxxxxxxxx>
Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
Tested-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Acked-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Tested-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230202073148.657746-3-sumit.garg@xxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
index 41b065f1be88c..13630e8078ff4 100644
--- a/arch/arm64/include/asm/debug-monitors.h
+++ b/arch/arm64/include/asm/debug-monitors.h
@@ -125,6 +125,7 @@ void user_regs_reset_single_step(struct user_pt_regs *regs,
void kernel_enable_single_step(struct pt_regs *regs);
void kernel_disable_single_step(void);
int kernel_active_single_step(void);
+void kernel_rewind_single_step(struct pt_regs *regs);
#ifdef CONFIG_HAVE_HW_BREAKPOINT
int reinstall_suspended_bps(struct pt_regs *regs);
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 501e835c65007..f5837937cd932 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -437,6 +437,11 @@ int kernel_active_single_step(void)
}
NOKPROBE_SYMBOL(kernel_active_single_step);
+void kernel_rewind_single_step(struct pt_regs *regs)
+{
+ set_regs_spsr_ss(regs);
+}
+
/* ptrace API */
void user_enable_single_step(struct task_struct *task)
{
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index 8815b5457dd0b..d7847ef10e9d3 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -234,6 +234,8 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
*/
if (!kernel_active_single_step())
kernel_enable_single_step(linux_regs);
+ else
+ kernel_rewind_single_step(linux_regs);
err = 0;
break;
default:
