Date:   Tue, 22 Nov 2022 07:16:05 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Song Chen <chensong_2000@....cn>
Cc:     rostedt@...dmis.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] kernel/trace: Introduce new APIs to process probe
 arguments

On Wed, 16 Nov 2022 20:25:07 +0800
Song Chen <chensong_2000@....cn> wrote:

> Introduce 3 new APIs:
> 1. trace_probe_get_data_size: get arguments' data size
> 2. trace_probe_store_args: store aruguments into ring buffer
> 3. trace_probe_print_args: print arguments into trace file
> 
> Those APIs are going to merge similar implementations respectively
> in kprobe/uprobe/eprobe.
> 
> Signed-off-by: Song Chen <chensong_2000@....cn>
> ---
>  kernel/trace/trace_probe.c        | 305 ++++++++++++++++++++++++++++++
>  kernel/trace/trace_probe.h        |   5 +
>  kernel/trace/trace_probe_common.h |  69 +++++++
>  kernel/trace/trace_probe_user.h   |  95 ++++++++++
>  4 files changed, 474 insertions(+)
>  create mode 100644 kernel/trace/trace_probe_common.h
>  create mode 100644 kernel/trace/trace_probe_user.h
> 
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 36dff277de46..303f057bd2f7 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -12,6 +12,9 @@
>  #define pr_fmt(fmt)	"trace_probe: " fmt
>  
>  #include "trace_probe.h"
> +#include "trace_probe_kernel.h"
> +#include "trace_probe_user.h"
> +#include "trace_probe_common.h"
>  
>  #undef C
>  #define C(a, b)		b
> @@ -1218,3 +1221,305 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
>  
>  	return ret;
>  }
> +
> +/* From the 2nd stage, routine is same */
> +static nokprobe_inline int
> +process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val,
> +			   void *dest, void *base, int flags)
> +{
> +	struct fetch_insn *s3 = NULL;
> +	int total = 0, ret = 0, i = 0;
> +	u32 loc = 0;
> +	unsigned long lval = val;
> +	int is_uprobe = flags & TRACE_EVENT_FL_UPROBE;
> +
> +stage2:
> +	/* 2nd stage: dereference memory if needed */
> +	do {
> +		if (code->op == FETCH_OP_DEREF) {
> +			lval = val;
> +			ret = probe_mem_read(&val, (void *)val + code->offset,
> +					     sizeof(val));
> +		} else if (code->op == FETCH_OP_UDEREF) {
> +			lval = val;
> +			ret = probe_mem_read_user(&val,
> +				 (void *)val + code->offset, sizeof(val));
> +		} else
> +			break;
> +		if (ret)
> +			return ret;
> +		code++;
> +	} while (1);
> +
> +	s3 = code;
> +stage3:
> +	/* 3rd stage: store value to buffer */
> +	if (unlikely(!dest)) {
> +		if (code->op == FETCH_OP_ST_STRING) {
> +			if (is_uprobe)
> +				ret = user_fetch_store_strlen(val + code->offset);
> +			else
> +				ret = kern_fetch_store_strlen(val + code->offset);
> +			code++;
> +			goto array;
> +		} else if (code->op == FETCH_OP_ST_USTRING) {
> +			if (is_uprobe)
> +				ret += user_fetch_store_strlen_user(val + code->offset);
> +			else
> +				ret += kern_fetch_store_strlen_user(val + code->offset);

Also, I would not like to see this "is_uprobe" check in the code. That is useless
when running this in the kernel. This is why I did this in trace_probe_tmpl.h as
an inlined function.

So, sorting print_args function is OK for me, but the process_fetch_insn* should be
kept as inlined. Maybe some common code can be move to the trace_probe_tmpl.h as
inlined functions?


> +			code++;
> +			goto array;
> +		} else
> +			return -EILSEQ;
> +	}
> +
> +	switch (code->op) {
> +	case FETCH_OP_ST_RAW:
> +		fetch_store_raw(val, code, dest);
> +		break;
> +	case FETCH_OP_ST_MEM:
> +		probe_mem_read(dest, (void *)val + code->offset, code->size);
> +		break;
> +	case FETCH_OP_ST_UMEM:
> +		probe_mem_read_user(dest, (void *)val + code->offset, code->size);
> +		break;
> +	case FETCH_OP_ST_STRING:
> +		loc = *(u32 *)dest;
> +		if (is_uprobe)
> +			ret = user_fetch_store_string(val + code->offset, dest, base);
> +		else
> +			ret = kern_fetch_store_string(val + code->offset, dest, base);
> +		break;
> +	case FETCH_OP_ST_USTRING:
> +		loc = *(u32 *)dest;
> +		if (is_uprobe)
> +			ret = user_fetch_store_string_user(val + code->offset, dest, base);
> +		else
> +			ret = kern_fetch_store_string_user(val + code->offset, dest, base);
> +		break;
> +	default:
> +		return -EILSEQ;
> +	}
> +	code++;
> +
> +	/* 4th stage: modify stored value if needed */
> +	if (code->op == FETCH_OP_MOD_BF) {
> +		fetch_apply_bitfield(code, dest);
> +		code++;
> +	}
> +
> +array:
> +	/* the last stage: Loop on array */
> +	if (code->op == FETCH_OP_LP_ARRAY) {
> +		total += ret;
> +		if (++i < code->param) {
> +			code = s3;
> +			if (s3->op != FETCH_OP_ST_STRING &&
> +			    s3->op != FETCH_OP_ST_USTRING) {
> +				dest += s3->size;
> +				val += s3->size;
> +				goto stage3;
> +			}
> +			code--;
> +			val = lval + sizeof(char *);
> +			if (dest) {
> +				dest += sizeof(u32);
> +				*(u32 *)dest = update_data_loc(loc, ret);
> +			}
> +			goto stage2;
> +		}
> +		code++;
> +		ret = total;
> +	}
> +
> +	return code->op == FETCH_OP_END ? ret : -EILSEQ;
> +}
> +
> +static unsigned long get_event_field(struct fetch_insn *code, void *rec)
> +{
> +	struct ftrace_event_field *field = code->data;
> +	unsigned long val;
> +	void *addr;
> +
> +	addr = rec + field->offset;
> +
> +	if (is_string_field(field)) {
> +		switch (field->filter_type) {
> +		case FILTER_DYN_STRING:
> +			val = (unsigned long)(rec + (*(unsigned int *)addr & 0xffff));
> +			break;
> +		case FILTER_RDYN_STRING:
> +			val = (unsigned long)(addr + (*(unsigned int *)addr & 0xffff));
> +			break;
> +		case FILTER_STATIC_STRING:
> +			val = (unsigned long)addr;
> +			break;
> +		case FILTER_PTR_STRING:
> +			val = (unsigned long)(*(char *)addr);
> +			break;
> +		default:
> +			WARN_ON_ONCE(1);
> +			return 0;
> +		}
> +		return val;
> +	}
> +
> +	switch (field->size) {
> +	case 1:
> +		if (field->is_signed)
> +			val = *(char *)addr;
> +		else
> +			val = *(unsigned char *)addr;
> +		break;
> +	case 2:
> +		if (field->is_signed)
> +			val = *(short *)addr;
> +		else
> +			val = *(unsigned short *)addr;
> +		break;
> +	case 4:
> +		if (field->is_signed)
> +			val = *(int *)addr;
> +		else
> +			val = *(unsigned int *)addr;
> +		break;
> +	default:
> +		if (field->is_signed)
> +			val = *(long *)addr;
> +		else
> +			val = *(unsigned long *)addr;
> +		break;
> +	}
> +	return val;
> +}
> +
> +/* Note that we don't verify it, since the code does not come from user space */
> +static int
> +process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
> +		   void *base, int flags)
> +{
> +	struct pt_regs *regs = rec;
> +	unsigned long val;
> +	int is_uprobe = flags & TRACE_EVENT_FL_UPROBE;
> +
> +retry:
> +	/* 1st stage: get value from context */
> +	switch (code->op) {
> +	case FETCH_OP_REG:
> +		val = regs_get_register(regs, code->param);
> +		break;
> +	case FETCH_OP_STACK:
> +		if (is_uprobe)
> +			val = get_user_stack_nth(regs, code->param);
> +		else
> +			val = regs_get_kernel_stack_nth(regs, code->param);
> +		break;

Ditto.

> +	case FETCH_OP_STACKP:
> +		if (is_uprobe)
> +			val = user_stack_pointer(regs);
> +		else
> +			val = kernel_stack_pointer(regs);
> +		break;
> +	case FETCH_OP_RETVAL:
> +		val = regs_return_value(regs);
> +		break;
> +	case FETCH_OP_IMM:
> +		val = code->immediate;
> +		break;
> +	case FETCH_OP_COMM:
> +		val = (unsigned long)current->comm;
> +		break;
> +	case FETCH_OP_DATA:
> +		val = (unsigned long)code->data;
> +		break;
> +#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
> +	case FETCH_OP_ARG:
> +		val = regs_get_kernel_argument(regs, code->param);
> +		break;
> +#endif
> +	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
> +		code++;
> +		goto retry;
> +	case FETCH_OP_TP_ARG:
> +		val = get_event_field(code, rec);
> +		break;
> +	default:
> +		return -EILSEQ;
> +	}
> +	code++;
> +
> +	return process_fetch_insn_bottom(code, val, dest, base, flags);
> +}
> +NOKPROBE_SYMBOL(process_fetch_insn)
> +
> +/* Sum up total data length for dynamic arrays (strings) */
> +int trace_probe_get_data_size(struct trace_probe *tp, struct pt_regs *regs)
> +{
> +	struct probe_arg *arg;
> +	int i, len, ret = 0;
> +	struct trace_event_call *call = trace_probe_event_call(tp);
> +
> +	for (i = 0; i < tp->nr_args; i++) {
> +		arg = tp->args + i;
> +		if (unlikely(arg->dynamic)) {
> +			len = process_fetch_insn(arg->code, regs, NULL, NULL, call->flags);
> +			if (len > 0)
> +				ret += len;
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +void trace_probe_store_args(void *data, struct trace_probe *tp, void *rec,
> +		 int header_size, int maxlen)
> +{
> +	struct probe_arg *arg;
> +	void *base = data - header_size;
> +	void *dyndata = data + tp->size;
> +	u32 *dl;	/* Data location */
> +	int ret, i;
> +	struct trace_event_call *call = trace_probe_event_call(tp);
> +
> +	for (i = 0; i < tp->nr_args; i++) {
> +		arg = tp->args + i;
> +		dl = data + arg->offset;
> +		/* Point the dynamic data area if needed */
> +		if (unlikely(arg->dynamic))
> +			*dl = make_data_loc(maxlen, dyndata - base);
> +		ret = process_fetch_insn(arg->code, rec, dl, base, call->flags);
> +		if (unlikely(ret < 0 && arg->dynamic)) {
> +			*dl = make_data_loc(0, dyndata - base);
> +		} else {
> +			dyndata += ret;
> +			maxlen -= ret;
> +		}
> +	}
> +}
> +
> +int trace_probe_print_args(struct trace_seq *s, struct probe_arg *args, int nr_args,
> +		 u8 *data, void *field)
> +{
> +	void *p;
> +	int i, j;
> +
> +	for (i = 0; i < nr_args; i++) {
> +		struct probe_arg *a = args + i;
> +
> +		trace_seq_printf(s, " %s=", a->name);
> +		if (likely(!a->count)) {
> +			if (!a->type->print(s, data + a->offset, field))
> +				return -ENOMEM;
> +			continue;
> +		}
> +		trace_seq_putc(s, '{');
> +		p = data + a->offset;
> +		for (j = 0; j < a->count; j++) {
> +			if (!a->type->print(s, p, field))
> +				return -ENOMEM;
> +			trace_seq_putc(s, j == a->count - 1 ? '}' : ',');
> +			p += a->type->size;
> +		}
> +	}
> +	return 0;
> +}
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index de38f1c03776..4f044047b748 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -343,6 +343,11 @@ int trace_probe_compare_arg_type(struct trace_probe *a, struct trace_probe *b);
>  bool trace_probe_match_command_args(struct trace_probe *tp,
>  				    int argc, const char **argv);
>  int trace_probe_create(const char *raw_command, int (*createfn)(int, const char **));
> +int trace_probe_get_data_size(struct trace_probe *tp, struct pt_regs *regs);
> +void trace_probe_store_args(void *data, struct trace_probe *tp, void *rec,
> +		 int header_size, int maxlen);
> +int trace_probe_print_args(struct trace_seq *s, struct probe_arg *args, int nr_args,
> +		 u8 *data, void *field);
>  
>  #define trace_probe_for_each_link(pos, tp)	\
>  	list_for_each_entry(pos, &(tp)->event->files, list)
> diff --git a/kernel/trace/trace_probe_common.h b/kernel/trace/trace_probe_common.h
> new file mode 100644
> index 000000000000..b8d77447fe0c
> --- /dev/null
> +++ b/kernel/trace/trace_probe_common.h

Please do not add an internal header file only just for 1 file. 

> @@ -0,0 +1,69 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __TRACE_PROBE_COMMON_H_
> +#define __TRACE_PROBE_COMMON_H_
> +
> +#define FAULT_STRING "(fault)"
> +
> +static nokprobe_inline void
> +fetch_store_raw(unsigned long val, struct fetch_insn *code, void *buf)
> +{
> +	switch (code->size) {
> +	case 1:
> +		*(u8 *)buf = (u8)val;
> +		break;
> +	case 2:
> +		*(u16 *)buf = (u16)val;
> +		break;
> +	case 4:
> +		*(u32 *)buf = (u32)val;
> +		break;
> +	case 8:
> +		//TBD: 32bit signed
> +		*(u64 *)buf = (u64)val;
> +		break;
> +	default:
> +		*(unsigned long *)buf = val;
> +	}
> +}
> +
> +static nokprobe_inline void
> +fetch_apply_bitfield(struct fetch_insn *code, void *buf)
> +{
> +	switch (code->basesize) {
> +	case 1:
> +		*(u8 *)buf <<= code->lshift;
> +		*(u8 *)buf >>= code->rshift;
> +		break;
> +	case 2:
> +		*(u16 *)buf <<= code->lshift;
> +		*(u16 *)buf >>= code->rshift;
> +		break;
> +	case 4:
> +		*(u32 *)buf <<= code->lshift;
> +		*(u32 *)buf >>= code->rshift;
> +		break;
> +	case 8:
> +		*(u64 *)buf <<= code->lshift;
> +		*(u64 *)buf >>= code->rshift;
> +		break;
> +	}
> +}
> +
> +static nokprobe_inline int
> +probe_mem_read_user(void *dest, void *src, size_t size)
> +{
> +	const void __user *uaddr =  (__force const void __user *)src;
> +
> +	return copy_from_user_nofault(dest, uaddr, size);
> +}
> +
> +static nokprobe_inline int
> +probe_mem_read(void *dest, void *src, size_t size)
> +{
> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> +	if ((unsigned long)src < TASK_SIZE)
> +		return probe_mem_read_user(dest, src, size);
> +#endif
> +	return copy_from_kernel_nofault(dest, src, size);
> +}
> +#endif /* __TRACE_PROBE_COMMON_H_ */
> diff --git a/kernel/trace/trace_probe_user.h b/kernel/trace/trace_probe_user.h
> new file mode 100644
> index 000000000000..2104ccb44d56
> --- /dev/null
> +++ b/kernel/trace/trace_probe_user.h

Ditto.

Thank you,

> @@ -0,0 +1,95 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __TRACE_PROBE_USER_H_
> +#define __TRACE_PROBE_USER_H_
> +
> +#define FAULT_STRING "(fault)"
> +
> +/*
> + * Fetch a null-terminated string. Caller MUST set *(u32 *)dest with max
> + * length and relative data location.
> + */
> +static nokprobe_inline int
> +user_fetch_store_string(unsigned long addr, void *dest, void *base)
> +{
> +	long ret;
> +	u32 loc = *(u32 *)dest;
> +	int maxlen  = get_loc_len(loc);
> +	u8 *dst = get_loc_data(dest, base);
> +	void __user *src = (void __force __user *) addr;
> +
> +	if (unlikely(!maxlen))
> +		return -ENOMEM;
> +
> +	if (addr == FETCH_TOKEN_COMM)
> +		ret = strlcpy(dst, current->comm, maxlen);
> +	else
> +		ret = strncpy_from_user(dst, src, maxlen);
> +	if (ret >= 0) {
> +		if (ret == maxlen)
> +			dst[ret - 1] = '\0';
> +		else
> +			/*
> +			 * Include the terminating null byte. In this case it
> +			 * was copied by strncpy_from_user but not accounted
> +			 * for in ret.
> +			 */
> +			ret++;
> +		*(u32 *)dest = make_data_loc(ret, (void *)dst - base);
> +	}
> +
> +	return ret;
> +}
> +
> +static nokprobe_inline int
> +user_fetch_store_string_user(unsigned long addr, void *dest, void *base)
> +{
> +	return user_fetch_store_string(addr, dest, base);
> +}
> +
> +/* Return the length of string -- including null terminal byte */
> +static nokprobe_inline int
> +user_fetch_store_strlen(unsigned long addr)
> +{
> +	int len;
> +	void __user *vaddr = (void __force __user *) addr;
> +
> +	if (addr == FETCH_TOKEN_COMM)
> +		len = strlen(current->comm) + 1;
> +	else
> +		len = strnlen_user(vaddr, MAX_STRING_SIZE);
> +
> +	return (len > MAX_STRING_SIZE) ? 0 : len;
> +}
> +
> +static nokprobe_inline int
> +user_fetch_store_strlen_user(unsigned long addr)
> +{
> +	return user_fetch_store_strlen(addr);
> +}
> +
> +#ifdef CONFIG_STACK_GROWSUP
> +static unsigned long adjust_stack_addr(unsigned long addr, unsigned int n)
> +{
> +	return addr - (n * sizeof(long));
> +}
> +#else
> +static unsigned long adjust_stack_addr(unsigned long addr, unsigned int n)
> +{
> +	return addr + (n * sizeof(long));
> +}
> +#endif
> +
> +static unsigned long get_user_stack_nth(struct pt_regs *regs, unsigned int n)
> +{
> +	unsigned long ret;
> +	unsigned long addr = user_stack_pointer(regs);
> +
> +	addr = adjust_stack_addr(addr, n);
> +
> +	if (copy_from_user(&ret, (void __force __user *) addr, sizeof(ret)))
> +		return 0;
> +
> +	return ret;
> +}
> +
> +#endif /* __TRACE_PROBE_USER_H_ */
> -- 
> 2.25.1
> 

Thanks,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>

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