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From:   Changbin Du <changbin.du@gmail.com>
To:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Changbin Du <changbin.du@gmail.com>
Subject: [PATCH v4] riscv: fix oops caused by irqsoff latency tracer
Date:   Sun, 13 Feb 2022 16:18:45 +0800
Message-Id: <20220213081845.9864-1-changbin.du@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The trace_hardirqs_{on,off}() require the caller to setup frame pointer
properly. This because these two functions use macro 'CALLER_ADDR1' (aka.
__builtin_return_address(1)) to acquire caller info. If the $fp is used
for other purpose, the code generated this macro (as below) could trigger
memory access fault.

   0xffffffff8011510e <+80>:    ld      a1,-16(s0)
   0xffffffff80115112 <+84>:    ld      s2,-8(a1)  # <-- paging fault here

The oops message during booting if compiled with 'irqoff' tracer enabled:
[    0.039615][    T0] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000f8
[    0.041925][    T0] Oops [#1]
[    0.042063][    T0] Modules linked in:
[    0.042864][    T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-rc1-00233-g9a20c48d1ed2 #29
[    0.043568][    T0] Hardware name: riscv-virtio,qemu (DT)
[    0.044343][    T0] epc : trace_hardirqs_on+0x56/0xe2
[    0.044601][    T0]  ra : restore_all+0x12/0x6e
[    0.044721][    T0] epc : ffffffff80126a5c ra : ffffffff80003b94 sp : ffffffff81403db0
[    0.044801][    T0]  gp : ffffffff8163acd8 tp : ffffffff81414880 t0 : 0000000000000020
[    0.044882][    T0]  t1 : 0098968000000000 t2 : 0000000000000000 s0 : ffffffff81403de0
[    0.044967][    T0]  s1 : 0000000000000000 a0 : 0000000000000001 a1 : 0000000000000100
[    0.045046][    T0]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
[    0.045124][    T0]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000054494d45
[    0.045210][    T0]  s2 : ffffffff80003b94 s3 : ffffffff81a8f1b0 s4 : ffffffff80e27b50
[    0.045289][    T0]  s5 : ffffffff81414880 s6 : ffffffff8160fa00 s7 : 00000000800120e8
[    0.045389][    T0]  s8 : 0000000080013100 s9 : 000000000000007f s10: 0000000000000000
[    0.045474][    T0]  s11: 0000000000000000 t3 : 7fffffffffffffff t4 : 0000000000000000
[    0.045548][    T0]  t5 : 0000000000000000 t6 : ffffffff814aa368
[    0.045620][    T0] status: 0000000200000100 badaddr: 00000000000000f8 cause: 000000000000000d
[    0.046402][    T0] [<ffffffff80003b94>] restore_all+0x12/0x6e

This because the $fp(aka. $s0) register is not used as frame pointer in the
assembly entry code.

	resume_kernel:
		REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
		bnez s0, restore_all
		REG_L s0, TASK_TI_FLAGS(tp)
                andi s0, s0, _TIF_NEED_RESCHED
                beqz s0, restore_all
                call preempt_schedule_irq
                j restore_all

To fix above issue, here we add one extra level wrapper for function
trace_hardirqs_{on,off}() so they can be safely called by low level entry
code.

Signed-off-by: Changbin Du <changbin.du@gmail.com>

---
v4: update explanation.
v3: fix warning reported by documentation system.
v2: fix compile warning.
---
 arch/riscv/kernel/Makefile    |  2 ++
 arch/riscv/kernel/entry.S     | 10 +++++-----
 arch/riscv/kernel/trace_irq.c | 27 +++++++++++++++++++++++++++
 arch/riscv/kernel/trace_irq.h | 11 +++++++++++
 4 files changed, 45 insertions(+), 5 deletions(-)
 create mode 100644 arch/riscv/kernel/trace_irq.c
 create mode 100644 arch/riscv/kernel/trace_irq.h

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 612556faa527..ffc87e76b1dd 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -51,6 +51,8 @@ obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
 
+obj-$(CONFIG_TRACE_IRQFLAGS)	+= trace_irq.o
+
 obj-$(CONFIG_RISCV_BASE_PMU)	+= perf_event.o
 obj-$(CONFIG_PERF_EVENTS)	+= perf_callchain.o
 obj-$(CONFIG_HAVE_PERF_REGS)	+= perf_regs.o
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index ed29e9c8f660..d6a46ed0bf05 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -108,7 +108,7 @@ _save_context:
 .option pop
 
 #ifdef CONFIG_TRACE_IRQFLAGS
-	call trace_hardirqs_off
+	call __trace_hardirqs_off
 #endif
 
 #ifdef CONFIG_CONTEXT_TRACKING
@@ -143,7 +143,7 @@ skip_context_tracking:
 	li t0, EXC_BREAKPOINT
 	beq s4, t0, 1f
 #ifdef CONFIG_TRACE_IRQFLAGS
-	call trace_hardirqs_on
+	call __trace_hardirqs_on
 #endif
 	csrs CSR_STATUS, SR_IE
 
@@ -234,7 +234,7 @@ ret_from_exception:
 	REG_L s0, PT_STATUS(sp)
 	csrc CSR_STATUS, SR_IE
 #ifdef CONFIG_TRACE_IRQFLAGS
-	call trace_hardirqs_off
+	call __trace_hardirqs_off
 #endif
 #ifdef CONFIG_RISCV_M_MODE
 	/* the MPP value is too large to be used as an immediate arg for addi */
@@ -270,10 +270,10 @@ restore_all:
 	REG_L s1, PT_STATUS(sp)
 	andi t0, s1, SR_PIE
 	beqz t0, 1f
-	call trace_hardirqs_on
+	call __trace_hardirqs_on
 	j 2f
 1:
-	call trace_hardirqs_off
+	call __trace_hardirqs_off
 2:
 #endif
 	REG_L a0, PT_STATUS(sp)
diff --git a/arch/riscv/kernel/trace_irq.c b/arch/riscv/kernel/trace_irq.c
new file mode 100644
index 000000000000..095ac976d7da
--- /dev/null
+++ b/arch/riscv/kernel/trace_irq.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Changbin Du <changbin.du@gmail.com>
+ */
+
+#include <linux/irqflags.h>
+#include <linux/kprobes.h>
+#include "trace_irq.h"
+
+/*
+ * trace_hardirqs_on/off require the caller to setup frame pointer properly.
+ * Otherwise, CALLER_ADDR1 might trigger an pagging exception in kernel.
+ * Here we add one extra level so they can be safely called by low
+ * level entry code which $fp is used for other purpose.
+ */
+
+void __trace_hardirqs_on(void)
+{
+	trace_hardirqs_on();
+}
+NOKPROBE_SYMBOL(__trace_hardirqs_on);
+
+void __trace_hardirqs_off(void)
+{
+	trace_hardirqs_off();
+}
+NOKPROBE_SYMBOL(__trace_hardirqs_off);
diff --git a/arch/riscv/kernel/trace_irq.h b/arch/riscv/kernel/trace_irq.h
new file mode 100644
index 000000000000..99fe67377e5e
--- /dev/null
+++ b/arch/riscv/kernel/trace_irq.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Changbin Du <changbin.du@gmail.com>
+ */
+#ifndef __TRACE_IRQ_H
+#define __TRACE_IRQ_H
+
+void __trace_hardirqs_on(void);
+void __trace_hardirqs_off(void);
+
+#endif /* __TRACE_IRQ_H */
-- 
2.32.0