Patch "arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step" has been added to the 5.10-stable tree

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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 5.10-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-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6d2e6eafe08e3dfe95c9e44e4118a1773a9dcc91
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 657c921fd784a..c16ed5b68768e 100644
--- a/arch/arm64/include/asm/debug-monitors.h
+++ b/arch/arm64/include/asm/debug-monitors.h
@@ -116,6 +116,7 @@ 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 fa76151de6ff1..38a0213fdbeee 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -439,6 +439,11 @@ 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 1a157ca33262d..e4e95821b1f6c 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -223,6 +223,8 @@ 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:



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