Messages in this thread Patch in this message |  | | Subject | Re: [PATCH RESEND v2 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe | From | Li Huafei <> | Date | Fri, 23 Sep 2022 16:43:43 +0800 |
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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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