Messages in this thread |  | | Date | Sat, 10 Sep 2022 12:25:39 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH RESEND v2 2/2] riscv: kprobe: Allow coexistence of ftrace and kprobe |
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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.
> > 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?
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 >
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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