After entering kgdb mode, 'stepi' may unexpectedly breaks the execution
somewhere in el1_irq.
This happens because a debug exception is always enabled in el1_irq
due to the following commit merged in v3.16:
commit 2a2830703a23 ("arm64: debug: avoid accessing mdscr_el1 on fault
paths where possible")
A pending interrupt can be taken after kgdb has enabled a software step,
but before a debug exception is actually taken.
This patch enforces interrupts to be masked while single stepping.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 3.16-
---
arch/arm64/kernel/kgdb.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index 59c4aec..6732a27 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -26,6 +26,7 @@
#include <linux/kgdb.h>
#include <linux/kprobes.h>
#include <linux/percpu.h>
+#include <asm/ptrace.h>
#include <asm/traps.h>
struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
@@ -109,6 +110,7 @@ struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
{ "fpcr", 4, -1 },
};
+static DEFINE_PER_CPU(unsigned int, kgdb_pstate);
static DEFINE_PER_CPU(struct irq_work, kgdb_irq_work);
char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs)
@@ -198,6 +200,10 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
err = 0;
break;
case 's':
+ /* mask interrupts while single stepping */
+ __this_cpu_write(kgdb_pstate, linux_regs->pstate);
+ linux_regs->pstate |= PSR_I_BIT;
+
/*
* Update step address value with address passed
* with step packet.
@@ -239,9 +245,18 @@ NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
{
+ unsigned int pstate;
+
kernel_disable_single_step();
atomic_set(&kgdb_cpu_doing_single_step, -1);
+ /* restore interrupt mask status */
+ pstate = __this_cpu_read(kgdb_pstate);
+ if (pstate & PSR_I_BIT)
+ regs->pstate |= PSR_I_BIT;
+ else
+ regs->pstate &= ~PSR_I_BIT;
+
kgdb_handle_exception(1, SIGTRAP, 0, regs);
return 0;
}
--
2.10.0
--
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