Messages in this thread |  | | Subject | Re: [PATCH RESEND v2 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe | From | Li Huafei <> | Date | Mon, 26 Sep 2022 21:40:38 +0800 |
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On 2022/9/25 20:45, Guo Ren wrote: > Hi Li, > > Current riscv ftrace detour instructions could be reduced to half [1]. > > Before optimization (16 byte): > <func_prolog>: > 0: REG_S ra, -SZREG(sp) > 4: auipc ra, ? > 8: jalr ?(ra) > 12: REG_L ra, -SZREG(sp) > (func_boddy) > > The previous implementation is from afc76b8b8011 ("riscv: Using > PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") > > After optimization (8 byte): > <func_prolog>: > 0: auipc t0, ? > 4: jalr t0, ?(t0) > (func_boddy) > > [1]: https://lore.kernel.org/linux-riscv/20220921034910.3142465-4-guoren@kernel.org/
Nice patch! Thank you for the information. I will update my patch based on it.
Thanks, Huafei
> > I'm appreciate you could base it on that patch. > > On Fri, Sep 23, 2022 at 4:43 PM Li Huafei <lihuafei1@huawei.com> wrote: >> >> Hi Masami, >> >> Thanks for your comment and sorry for the late reply. >> >> On 2022/9/10 11:25, Masami Hiramatsu (Google) wrote: >>> Hi Li, >>> >>> On Fri, 9 Sep 2022 10:36:25 +0800 >>> Li Huafei <lihuafei1@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. >>> >>> Yes, this must be solved by CONFIG_HAVE_KPROBES_ON_FTRACE. >>> >>>> >>>> # 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. >>> >>> In this case, we should NOT probe such address by kprobes. The reason >>> why I introduce the CONFIG_KPROBES_ON_FTRACE is to avoid this issue. >>> >> >> Yes, I think CONFIG_KPROBES_ON_FTRACE is mainly intended to solve the >> problem of coexistence with ftrace and not just as an optimization. >> >>> >>>> >>>> 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 func+4, func+8 and func+12 will be >>>> changed to func+0. 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+4' >> kprobe_events >>>> # echo 'p cmdline_proc_show+8' >> kprobe_events >>>> # echo 'p cmdline_proc_show+12' >> kprobe_events >>>> # echo 'p cmdline_proc_show+16' >> kprobe_events >>> >>> Oh, no, I meant, if it is a 16 byte virtual insturiction, it should >>> reject probing the address inside the instruction. It is rejected as >>> same as the case you probe "function+1" address (that is not an >>> instruction boundary, right?) >>> >>> So, it should reject it instead of modifying the probed address. (Return >>> -EILSEQ) It is usual there is any instruction which can not be probed. >>> >>> Or, is there any real reason you "have to" probe such intermediate >>> address? >> >> No. In fact in my first version of the patch(see [1]), >> arch_adjust_kprobe_addr() returned -EILSEQ when probing intermediate >> addresses. but Guo pointed out that I changed the API and it did. >> >> Currently there are x86 & powerpc using their own arch_adjust_kprobe_addr(). >> >> On x86, when X86_KERNEL_IBT is enabled, arch_adjust_kprobe_addr() >> adjusts sym+0 (endbr) to sym+4 (ftrace location). If we probe through >> kprobe_events, we get: >> >> # cd /sys/kernel/debug/tracing/ >> # 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 >> # cat /sys/kernel/debug/kprobes/list >> ffffffff812d31e4 k cmdline_proc_show+0x4 [DISABLED][FTRACE] >> ffffffff812d31e4 k cmdline_proc_show+0x4 [DISABLED][FTRACE] >> >> '/sys/kernel/debug/tracing/events/kprobes/' shows that we generated two >> probe_events, but '/sys/kernel/debug/kprobes/list' shows that it is the >> same address with two probes (aggr_kprobe). >> >> The same is true for powerpc: >> >> # cd /sys/kernel/debug/tracing/ >> # echo 'p cmdline_proc_show' > kprobe_events >> # echo 'p cmdline_proc_show+12' >> kprobe_events >> # ls events/kprobes/ >> enable p_cmdline_proc_show_0 >> filter p_cmdline_proc_show_12 >> # cat /sys/kernel/debug/kprobes/list >> c000000000515c0c k cmdline_proc_show+0xc [DISABLED][FTRACE] >> c000000000515c0c k cmdline_proc_show+0xc [DISABLED][FTRACE] >> c0000000000508c0 k __kretprobe_trampoline+0x0 [OPTIMIZED] >> >> So for kprobe, can we consider all instructions before the "real" >> instruction of the function as a virtual instruction? And then refuse to >> probe the intermediate address of this virtual instruction to avoid >> ambiguity for the user here. >> >> [1] >> https://lore.kernel.org/lkml/20220426015751.88582-2-lihuafei1@huawei.com/ >> >> Thanks, >> Huafei >> >>> >>> Thank you, >>> >>>> # ls events/kprobes/ >>>> enable p_cmdline_proc_show_12 p_cmdline_proc_show_8 >>>> filter p_cmdline_proc_show_16 >>>> p_cmdline_proc_show_0 p_cmdline_proc_show_4 >>>> # echo 1 > events/kprobes/enable >>>> # cat ../kprobes/list >>>> ffffffff8025cba4 k cmdline_proc_show+0x0 [FTRACE] >>>> ffffffff8025cba4 k cmdline_proc_show+0x0 [FTRACE] >>>> ffffffff8025cba4 k cmdline_proc_show+0x0 [FTRACE] >>>> ffffffff8025cba4 k cmdline_proc_show+0x0 [FTRACE] >>>> ffffffff8025cbb4 k cmdline_proc_show+0x10 >>>> # cat /proc/cmdline >>>> nokaslr rootwait root=/dev/vda rw >>>> # cat trace >>>> # tracer: function >>>> # >>>> # entries-in-buffer/entries-written: 6/6 #P:4 >>>> # >>>> # _-----=> irqs-off/BH-disabled >>>> # / _----=> need-resched >>>> # | / _---=> hardirq/softirq >>>> # || / _--=> preempt-depth >>>> # ||| / _-=> migrate-disable >>>> # |||| / delay >>>> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION >>>> # | | | ||||| | | >>>> cat-144 [000] ...2. 179.164908: p_cmdline_proc_show_12: (cmdline_proc_show+0x0/0x46) >>>> cat-144 [000] ...2. 179.165617: p_cmdline_proc_show_8: (cmdline_proc_show+0x0/0x46) >>>> cat-144 [000] ...2. 179.165653: p_cmdline_proc_show_4: (cmdline_proc_show+0x0/0x46) >>>> cat-144 [000] ...2. 179.165655: p_cmdline_proc_show_0: (cmdline_proc_show+0x0/0x46) >>>> cat-144 [000] ...2. 179.165837: cmdline_proc_show <-seq_read_iter >>>> cat-144 [000] d.... 179.166099: 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") >>>> Suggested-by: Guo Ren <guoren@kernel.org> >>>> Signed-off-by: Li Huafei <lihuafei1@huawei.com> >>>> --- >>>> v1: https://lore.kernel.org/lkml/20220426015751.88582-1-lihuafei1@huawei.com/ >>>> v2: https://lore.kernel.org/lkml/20220819025522.154189-2-lihuafei1@huawei.com/ >>>> >>>> v2 RESEND: >>>> - Rebase onto v6.0-rc4. >>>> >>>> Changlog in v1 -> v2: >>>> - Allows probing func+offs(<16) instead of returning -EILSEQ, which >>>> does not change the arch_adjust_kprobe_addr() interface convention. >>>> - ftrace_location(addr) is unnecessary, consistent with powerpc and >>>> x86. >>>> >>>> arch/riscv/include/asm/ftrace.h | 26 ++++++++++++++++++++++++++ >>>> arch/riscv/kernel/ftrace.c | 26 -------------------------- >>>> arch/riscv/kernel/probes/kprobes.c | 20 ++++++++++++++++++++ >>>> 3 files changed, 46 insertions(+), 26 deletions(-) >>>> >>>> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h >>>> index 04dad3380041..c59e4a63f1c1 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 >>>> >>>> +/* >>>> + * Put 16 bytes at the front of the function within the 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 552088e9acc4..9d951aab662a 100644 >>>> --- a/arch/riscv/kernel/ftrace.c >>>> +++ b/arch/riscv/kernel/ftrace.c >>>> @@ -70,32 +70,6 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target, >>>> return 0; >>>> } >>>> >>>> -/* >>>> - * Put 16 bytes at the front of the function within the 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}; >>>> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c >>>> index e6e950b7cf32..ef7aabec9681 100644 >>>> --- a/arch/riscv/kernel/probes/kprobes.c >>>> +++ b/arch/riscv/kernel/probes/kprobes.c >>>> @@ -21,6 +21,26 @@ 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. func+4, func+8 and func+12 will be >>>> + * changed to func+0. 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) >>>> + 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); >>>> -- >>>> 2.17.1 >>>> >>> >>> > > >
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