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

From: Guo Ren
Date: Tue Apr 26 2022 - 04:17:09 EST

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On Tue, Apr 26, 2022 at 4:01 PM Guo Ren <guoren@xxxxxxxxxx> wrote:
>
> On Tue, Apr 26, 2022 at 9:59 AM Li Huafei <lihuafei1@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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.
Typo: we shouldn't 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);
> + }
> +}
Another better implementation:
+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.
+ */
+ offset = 0;
+ }
+
+ *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);
>
> > +
> > + *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/

--
Best Regards
Guo Ren

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

Next message: Mark-PK Tsai: "Re: [PATCH v3 1/2] tracing: Avoid adding tracer option before update_tracer_options"
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In reply to: Guo Ren: "Re: [PATCH 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe"
Next in thread: Li Huafei: "Re: [PATCH 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe"
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