Messages in this thread |  | | From | Guo Ren <> | Date | Sun, 25 Sep 2022 20:45:40 +0800 | Subject | Re: [PATCH RESEND v2 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe |
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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/
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 > >> > > > >
-- Best Regards Guo Ren
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