[PATCH 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe

Guo Ren guoren at kernel.org
Tue Apr 26 01:01:06 PDT 2022


On Tue, Apr 26, 2022 at 9:59 AM Li Huafei <lihuafei1 at huawei.com> wrote:
>
> When using ftrace and kprobe at the same time, it was found that one
> might cause the other to be unavailable. This can be reproduced by the
> following steps.
>
>   # cd /sys/kernel/debug/tracing/
>   # echo cmdline_proc_show > set_ftrace_filter
>   # echo function > current_tracer
>   # echo 'p cmdline_proc_show' > kprobe_events
>   # echo 'p cmdline_proc_show+4' >> kprobe_events
>   # ls events/kprobes/
>   enable                 p_cmdline_proc_show_0
>   filter                 p_cmdline_proc_show_4
>   # echo 1 > events/kprobes/p_cmdline_proc_show_4/enable
>   # echo 1 > events/kprobes/p_cmdline_proc_show_0/enable
>   [  129.830108] 00000000ebed457d: expected (ffdb0097 4f0080e7) but got (00100073 4f0080e7)
>   [  129.835990] ------------[ ftrace bug ]------------
>   [  129.839510] ftrace failed to modify
>   [  129.839536] [<ffffffff80258910>] cmdline_proc_show+0x0/0x46
>   [  129.845831]  actual:   23:3c:11:fe:73:00:10:00
>   [  129.849299] Updating ftrace call site to call a different ftrace function
>   [  129.853998] ftrace record flags: e0000002
>   [  129.856771]  (2) R
>   [  129.856771]  expected tramp: ffffffff80008e60
>   [  129.861688] ------------[ cut here ]------------
>   [  129.865092] WARNING: CPU: 0 PID: 14 at kernel/trace/ftrace.c:2085 ftrace_bug+0x21a/0x24c
>   [  129.870949] Modules linked in:
>   [  129.873301] CPU: 0 PID: 14 Comm: migration/0 Not tainted 5.18.0-rc3-00002-gd8bfcd250f58 #6
>   [  129.879217] Hardware name: riscv-virtio,qemu (DT)
>   [  129.882666] Stopper: multi_cpu_stop+0x0/0x168 <- stop_machine_cpuslocked+0xfa/0x12e
>   [  129.888430] epc : ftrace_bug+0x21a/0x24c
>   [  129.891254]  ra : ftrace_bug+0x21a/0x24c
>   [  129.894057] epc : ffffffff807c3bee ra : ffffffff807c3bee sp : ff20000000283c80
>   [  129.899144]  gp : ffffffff813a83b8 tp : ff60000080021600 t0 : ffffffff804155c0
>   [  129.904257]  t1 : 0720072007200720 t2 : 7420646574636570 s0 : ff20000000283cb0
>   [  129.909402]  s1 : ff6000007fe622a0 a0 : 0000000000000022 a1 : c0000000ffffefff
>   [  129.914472]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : 341adec112294700
>   [  129.919487]  a5 : 341adec112294700 a6 : 0000000000000730 a7 : 0000000000000030
>   [  129.924595]  s2 : ffffffff80258910 s3 : ffffffffffffffea s4 : 0000000000000000
>   [  129.929776]  s5 : 0000000000000a35 s6 : ffffffff80d667c8 s7 : ff6000007fe04000
>   [  129.934892]  s8 : 0000000000000004 s9 : 0000000000000002 s10: 0000000000000001
>   [  129.939992]  s11: 0000000000000003 t3 : ff6000007ff20f00 t4 : ff6000007ff20f00
>   [  129.945134]  t5 : ff6000007ff20000 t6 : ff200000002839c8
>   [  129.948838] status: 0000000000000100 badaddr: 0000000000000000 cause: 0000000000000003
>   [  129.954580] [<ffffffff800bf110>] ftrace_replace_code+0xce/0xd0
>   [  129.958771] [<ffffffff800bf280>] ftrace_modify_all_code+0xb4/0x12c
>   [  129.964420] [<ffffffff800bf30a>] __ftrace_modify_code+0x12/0x1c
>   [  129.969163] [<ffffffff800b4ea4>] multi_cpu_stop+0x9a/0x168
>   [  129.973035] [<ffffffff800b4b1c>] cpu_stopper_thread+0xb4/0x15e
>   [  129.977205] [<ffffffff8003457a>] smpboot_thread_fn+0x106/0x1e4
>   [  129.981277] [<ffffffff80030ca6>] kthread+0xee/0x108
>   [  129.984763] [<ffffffff800039ba>] ret_from_exception+0x0/0xc
>   [  129.988809] ---[ end trace 0000000000000000 ]---
>   # cat trace
>   # tracer: function
>   #
>   # WARNING: FUNCTION TRACING IS CORRUPTED
>   #          MAY BE MISSING FUNCTION EVENTS
>   # entries-in-buffer/entries-written: 0/0   #P:4
>   #
>   #                                _-----=> irqs-off/BH-disabled
>   #                               / _----=> need-resched
>   #                              | / _---=> hardirq/softirq
>   #                              || / _--=> preempt-depth
>   #                              ||| / _-=> migrate-disable
>   #                              |||| /     delay
>   #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
>   #              | |         |   |||||     |         |
>
> As you can see, the ftrace functionality is broken. This is because
> DYNAMIC_FTRACE uses 4 instructions to make the jump from the function
> entry to the ftrace trampoline.
>
> After 'echo function > current_tracer':
>
>   <cmdline_proc_show>:
>     0xffffffff80258910 <+0>:     sd      ra,-8(sp)
>     0xffffffff80258914 <+4>:     auipc   ra,0xffdb0
>     0xffffffff80258918 <+8>:     jalr    1264(ra) # 0xffffffff80008e04 <ftrace_caller>
>     0xffffffff8025891c <+12>:    ld      ra,-8(sp)
>
> After 'echo 1 > events/kprobes/p_cmdline_proc_show_4/enable':
>
>   <cmdline_proc_show>:
>     0xffffffff80258910 <+0>:     sd      ra,-8(sp)
>     0xffffffff80258914 <+4>:     ebreak
>     0xffffffff80258918 <+8>:     jalr    1264(ra)
>     0xffffffff8025891c <+12>:    ld      ra,-8(sp)
>
> This time the second instruction is replaced with a breakpoint
> instruction and the ftrace-related instructions are broken. Then, when
> enabling 'p_cmdline_proc_show_0', a regs ftrace handler is registered
> based on KPROBES_ON_FTRACE, ftrace_modify_call() changes 'ftrace_caller'
> to 'ftrace_regs_caller', and checks for ftrace-related instructions is
> modified or not. Here it has been modified, causing ftrace to report a
> warning and disable itself.
>
> In turn, the breakpoints inserted by kprobe may be overwritten by
> ftrace.
>
> The problem is that we think that only the first instruction address at
> the function entry is needed for ftrace, but it is actually the first 4.
> As Masami mentioned in [1], we can treat the first 4 instructions as a
> 16-byte virtual instruction, and we can probe func+0 based on
> KPROBES_ON_FTRACE, but not func+4, func+8 and func+12. This way, ftrace
> and kprobe do not bother each other and can coexist.
>
> After this patch:
>
>   # cd /sys/kernel/debug/tracing/
>   # echo cmdline_proc_show > set_ftrace_filter
>   # echo function > current_tracer
>   # echo 'p cmdline_proc_show' > kprobe_events
>   # echo 'p cmdline_proc_show' > kprobe_events
>   # echo 'p cmdline_proc_show+4' >> kprobe_events
>   sh: write error: Invalid or incomplete multibyte or wide character
>   # echo 'p cmdline_proc_show+8' >> kprobe_events
>   sh: write error: Invalid or incomplete multibyte or wide character
>   # echo 'p cmdline_proc_show+12' >> kprobe_events
>   sh: write error: Invalid or incomplete multibyte or wide character
>   # echo 'p cmdline_proc_show+16' >> kprobe_events
>   # ls events/kprobes/
>   enable                  p_cmdline_proc_show_0
>   filter                  p_cmdline_proc_show_16
>   # echo 1 > events/kprobes/enable
>   # cat ../kprobes/list
>   ffffffff80258b14  k  cmdline_proc_show+0x0    [FTRACE]
>   ffffffff80258b24  k  cmdline_proc_show+0x10
>   # cat /proc/cmdline
>   nokaslr rootwait root=/dev/vda rw
>   # cat trace
>   # tracer: function
>   #
>   # entries-in-buffer/entries-written: 3/3   #P:4
>   #
>   #                                _-----=> irqs-off/BH-disabled
>   #                               / _----=> need-resched
>   #                              | / _---=> hardirq/softirq
>   #                              || / _--=> preempt-depth
>   #                              ||| / _-=> migrate-disable
>   #                              |||| /     delay
>   #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
>   #              | |         |   |||||     |         |
>                cat-142     [000] ...2.   181.493233: p_cmdline_proc_show_0: (cmdline_proc_show+0x0/0x46)
>                cat-142     [000] ...2.   181.494271: cmdline_proc_show <-seq_read_iter
>                cat-142     [000] d....   181.494573: p_cmdline_proc_show_16: (cmdline_proc_show+0x10/0x46)
>
> [1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20191218140622.57bbaca5@xhacker.debian/
>
> Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
> Signed-off-by: Li Huafei <lihuafei1 at huawei.com>
> ---
>  arch/riscv/kernel/probes/kprobes.c | 31 ++++++++++++++++++++++++++++++
>  kernel/kprobes.c                   |  2 +-
>  2 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index e6e950b7cf32..ebe32eb6c349 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -21,6 +21,37 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>  static void __kprobes
>  post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
> +                                        bool *on_func_entry)
> +{
> +       unsigned long faddr = ftrace_location(addr);
> +
> +       /*
> +        * The first 4 instructions at the beginning of the ftraced function
> +        * are used as a jump to ftrace trampoline, which we can think of as
> +        * a 16-byte virtual instruction. This allows the function entry to be
> +        * probed with the help of KPROBES_ON_FTRACE and does not break ftrace
> +        * functionality.
> +        */
> +       if (faddr && offset <= 12) {
> +               /*
> +                * As mentioned above, we treat the first 4 instructions of
> +                * the ftraced function as a virtual instruction, so that we
> +                * can only probe func+0, not func+4, func+8 and func+12.
> +                */
> +               if (offset)
> +                       return ERR_PTR(-EILSEQ);
Nak, we should change API in the patch.

Reference below:

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 04dad3380041..4fbab6b89be3 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -77,6 +77,32 @@ do {
                 \
  */
 #define MCOUNT_INSN_SIZE 8

+/*
+ * Put16 bytes at the front of function within patchable function entry
+ * nops' area.
+ *
+ * 0: REG_S  ra, -SZREG(sp)
+ * 1: auipc  ra, 0x?
+ * 2: jalr   -?(ra)
+ * 3: REG_L  ra, -SZREG(sp)
+ *
+ * So the opcodes is:
+ * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
+ * 1: 0x???????? -> auipc
+ * 2: 0x???????? -> jalr
+ * 3: 0xff813083 (ld)/0xffc12083 (lw)
+ */
+#if __riscv_xlen == 64
+#define INSN0  0xfe113c23
+#define INSN3  0xff813083
+#elif __riscv_xlen == 32
+#define INSN0  0xfe112e23
+#define INSN3  0xffc12083
+#endif
+
+#define FUNC_ENTRY_SIZE        16
+#define FUNC_ENTRY_JMP 4
+
 #ifndef __ASSEMBLY__
 struct dyn_ftrace;
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 4716f4cdc038..be51aa87134e 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -72,32 +72,6 @@ static int __ftrace_modify_call(unsigned long
hook_pos, unsigned long target,
        return 0;
 }

-/*
- * Put 5 instructions with 16 bytes at the front of function within
- * patchable function entry nops' area.
- *
- * 0: REG_S  ra, -SZREG(sp)
- * 1: auipc  ra, 0x?
- * 2: jalr   -?(ra)
- * 3: REG_L  ra, -SZREG(sp)
- *
- * So the opcodes is:
- * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
- * 1: 0x???????? -> auipc
- * 2: 0x???????? -> jalr
- * 3: 0xff813083 (ld)/0xffc12083 (lw)
- */
-#if __riscv_xlen == 64
-#define INSN0  0xfe113c23
-#define INSN3  0xff813083
-#elif __riscv_xlen == 32
-#define INSN0  0xfe112e23
-#define INSN3  0xffc12083
-#endif
-
-#define FUNC_ENTRY_SIZE        16
-#define FUNC_ENTRY_JMP 4
-
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
        unsigned int call[4] = {INSN0, 0, 0, INSN3};
@@ -124,7 +98,6 @@ int ftrace_make_nop(struct module *mod, struct
dyn_ftrace *rec,
        return 0;
 }

-
 /*
  * This is called early on, and isn't wrapped by
  * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
diff --git a/arch/riscv/kernel/probes/kprobes.c
b/arch/riscv/kernel/probes/kprobes.c
index e6e950b7cf32..c16a819a81c1 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -21,6 +21,33 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 static void __kprobes
 post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);

+#ifdef CONFIG_DYNAMIC_FTRACE
+kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned
long offset,
+                                        bool *on_func_entry)
+{
+       /*
+        * The first 4 instructions at the beginning of the ftraced function
+        * are used as a jump to ftrace trampoline, which we can think of as
+        * a 16-byte virtual instruction. This allows the function entry to be
+        * probed with the help of KPROBES_ON_FTRACE and does not break ftrace
+        * functionality.
+        */
+       if (offset < FUNC_ENTRY_SIZE) {
+               /*
+                * As mentioned above, we treat the first 4 instructions of
+                * the ftraced function as a virtual instruction, so that we
+                * can only probe func+0, and func+4, func+8 and func+12
+                * would be changed to func+0.
+                */
+               *on_func_entry = true;
+               return (kprobe_opcode_t *)ftrace_location(addr);
+       } else {
+               *on_func_entry = false;
+               return (kprobe_opcode_t *)(addr + offset);
+       }
+}
+#endif
+
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
        unsigned long offset = GET_INSN_LENGTH(p->opcode);

> +
> +               *on_func_entry = true;
> +               return (kprobe_opcode_t *)faddr;
> +       }
> +
> +       *on_func_entry = !offset;
> +       return (kprobe_opcode_t *)(addr + offset);
> +}
> +#endif
> +
>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>  {
>         unsigned long offset = GET_INSN_LENGTH(p->opcode);
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index dbe57df2e199..b41de7ce8bff 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1553,7 +1553,7 @@ _kprobe_addr(kprobe_opcode_t *addr, const char *symbol_name,
>          * at the start of the function.
>          */
>         addr = arch_adjust_kprobe_addr((unsigned long)addr, offset, on_func_entry);
> -       if (addr)
> +       if (IS_ERR(addr) || addr)
Nak, If you really want to change API, please send another patch and
add ftrace_location(addr) in x86 & powerpc, firstly.

>                 return addr;
>
>  invalid:
> --
> 2.17.1
>



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/



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