Subject: Re: [PATCH 1/2] bpf: Remove struct bpf_verifier_env argument from print_bpf_insn

From: Jiri Olsa <[email-masked]>
Date: Thu, 22 Mar 2018 16:57:23 +0100

On Thu, Mar 22, 2018 at 03:35:42PM +0000, Quentin Monnet wrote:
> 2018-03-22 14:32 UTC+0100 ~ Jiri Olsa <[email-masked]>
> > On Thu, Mar 22, 2018 at 10:34:18AM +0100, Daniel Borkmann wrote:
> >> On 03/21/2018 07:37 PM, Jiri Olsa wrote:
> >>> On Wed, Mar 21, 2018 at 05:25:33PM +0000, Quentin Monnet wrote:
> >>>> 2018-03-21 16:02 UTC+0100 ~ Jiri Olsa <[email-masked]>
> >>>>> We use print_bpf_insn in user space (bpftool and soon perf),
> >>>>> so it'd be nice to keep it generic and strip it off the kernel
> >>>>> struct bpf_verifier_env argument.
> >>>>>
> >>>>> This argument can be safely removed, because its users can
> >>>>> use the struct bpf_insn_cbs::private_data to pass it.
> >>>>>
> >>>>> Signed-off-by: Jiri Olsa <[email-masked]>
> >>>>> ---
> >>>>>  kernel/bpf/disasm.c   | 52 +++++++++++++++++++++++++--------------------------
> >>>>>  kernel/bpf/disasm.h   |  5 +----
> >>>>>  kernel/bpf/verifier.c |  6 +++---
> >>>>>  3 files changed, 30 insertions(+), 33 deletions(-)
> >>>>
> >>>> [...]
> >>>>
> >>>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> >>>>> index c6eff108aa99..9f27d3fa7259 100644
> >>>>> --- a/kernel/bpf/verifier.c
> >>>>> +++ b/kernel/bpf/verifier.c
> >>>>> @@ -202,8 +202,7 @@ EXPORT_SYMBOL_GPL(bpf_verifier_log_write);
> >>>>>   * generic for symbol export. The function was renamed, but not the calls in
> >>>>>   * the verifier to avoid complicating backports. Hence the alias below.
> >>>>>   */
> >>>>> -static __printf(2, 3) void verbose(struct bpf_verifier_env *env,
> >>>>> -				   const char *fmt, ...)
> >>>>> +static __printf(2, 3) void verbose(void *private_data, const char *fmt, ...)
> >>>>>  	__attribute__((alias("bpf_verifier_log_write")));
> >>>>
> >>>> Just as a note, verbose() will be aliased to a function whose prototype
> >>>> differs (bpf_verifier_log_write() still expects a struct
> >>>> bpf_verifier_env as its first argument). I am not so familiar with
> >>>> function aliases, could this change be a concern?
> >>>
> >>> yea, but as it was pointer for pointer switch I did not
> >>> see any problem with that.. I'll check more
> >>
> >> Ok, holding off for now until we have clarification. Other option could also
> >> be to make it void *private_data everywhere and for the kernel writer then
> >> do struct bpf_verifier_env *env = private_data.
> > 
> > can't find much info about the alias behaviour for this
> > case.. so how about having separate function for the
> > print_cb like below.. I still need to test it
> 
> I have nothing against splitting the function. This is a solution I
> considered for verbose() and bpf_verifier_log_write(), before switching
> to function alias (on Daniel's suggestion) because the code would be
> identical for the two separate functions at that time. But with your
> change they would not have the same signature anymore, so it sounds
> reasonable. Just a note below...
> 
> > 
> > thanks,
> > jirka
> > 
> > 
> > ---
> >  kernel/bpf/disasm.c   | 52 +++++++++++++++++++++++++--------------------------
> >  kernel/bpf/disasm.h   |  5 +----
> >  kernel/bpf/verifier.c | 41 +++++++++++++++++++++++++++++-----------
> >  3 files changed, 57 insertions(+), 41 deletions(-)
> > 
> 
> [...]
> 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index e9f7c20691c1..69bf7590877c 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -168,23 +168,16 @@ struct bpf_call_arg_meta {
> >  
> >  static DEFINE_MUTEX(bpf_verifier_lock);
> >  
> > -/* log_level controls verbosity level of eBPF verifier.
> > - * bpf_verifier_log_write() is used to dump the verification trace to the log,
> > - * so the user can figure out what's wrong with the program
> > - */
> > -__printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
> > -					   const char *fmt, ...)
> > +static void log_write(struct bpf_verifier_env *env, const char *fmt,
> > +		      va_list args)
> >  {
> >  	struct bpf_verifer_log *log = &env->log;
> >  	unsigned int n;
> > -	va_list args;
> >  
> >  	if (!log->level || !log->ubuf || bpf_verifier_log_full(log))
> >  		return;
> >  
> > -	va_start(args, fmt);
> >  	n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
> > -	va_end(args);
> >  
> >  	WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
> >  		  "verifier log line truncated - local buffer too short\n");
> > @@ -197,7 +190,32 @@ __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
> >  	else
> >  		log->ubuf = NULL;
> >  }
> > +
> > +/* log_level controls verbosity level of eBPF verifier.
> > + * bpf_verifier_log_write() is used to dump the verification trace to the log,
> > + * so the user can figure out what's wrong with the program
> > + */
> > +__printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
> > +					   const char *fmt, ...)
> > +{
> > +	va_list args;
> > +
> > +	va_start(args, fmt);
> > +	log_write(env, fmt, args);
> > +	va_end(args);
> > +}
> >  EXPORT_SYMBOL_GPL(bpf_verifier_log_write);
> > +
> > +__printf(2, 3) static void print_ins(void *private_data,
> > +				     const char *fmt, ...)
> 
> Unless I am mistaken, you could just call this one "verbose()" and
> simply remove the function alias?

right you are ;-) I haven't realized that struct bpf_verifier_env *env
will cleanly cast to void * 

new version attached.. I'll make some tests and send full patch

jirka

---
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 8740406df2cd..d6b76377cb6e 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -113,16 +113,16 @@ static const char *const bpf_jmp_string[16] = {
 };
 
 static void print_bpf_end_insn(bpf_insn_print_t verbose,
-			       struct bpf_verifier_env *env,
+			       void *private_data,
 			       const struct bpf_insn *insn)
 {
-	verbose(env, "(%02x) r%d = %s%d r%d\n", insn->code, insn->dst_reg,
+	verbose(private_data, "(%02x) r%d = %s%d r%d\n",
+		insn->code, insn->dst_reg,
 		BPF_SRC(insn->code) == BPF_TO_BE ? "be" : "le",
 		insn->imm, insn->dst_reg);
 }
 
 void print_bpf_insn(const struct bpf_insn_cbs *cbs,
-		    struct bpf_verifier_env *env,
 		    const struct bpf_insn *insn,
 		    bool allow_ptr_leaks)
 {
@@ -132,23 +132,23 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 	if (class == BPF_ALU || class == BPF_ALU64) {
 		if (BPF_OP(insn->code) == BPF_END) {
 			if (class == BPF_ALU64)
-				verbose(env, "BUG_alu64_%02x\n", insn->code);
+				verbose(cbs->private_data, "BUG_alu64_%02x\n", insn->code);
 			else
-				print_bpf_end_insn(verbose, env, insn);
+				print_bpf_end_insn(verbose, cbs->private_data, insn);
 		} else if (BPF_OP(insn->code) == BPF_NEG) {
-			verbose(env, "(%02x) r%d = %s-r%d\n",
+			verbose(cbs->private_data, "(%02x) r%d = %s-r%d\n",
 				insn->code, insn->dst_reg,
 				class == BPF_ALU ? "(u32) " : "",
 				insn->dst_reg);
 		} else if (BPF_SRC(insn->code) == BPF_X) {
-			verbose(env, "(%02x) %sr%d %s %sr%d\n",
+			verbose(cbs->private_data, "(%02x) %sr%d %s %sr%d\n",
 				insn->code, class == BPF_ALU ? "(u32) " : "",
 				insn->dst_reg,
 				bpf_alu_string[BPF_OP(insn->code) >> 4],
 				class == BPF_ALU ? "(u32) " : "",
 				insn->src_reg);
 		} else {
-			verbose(env, "(%02x) %sr%d %s %s%d\n",
+			verbose(cbs->private_data, "(%02x) %sr%d %s %s%d\n",
 				insn->code, class == BPF_ALU ? "(u32) " : "",
 				insn->dst_reg,
 				bpf_alu_string[BPF_OP(insn->code) >> 4],
@@ -157,46 +157,46 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 		}
 	} else if (class == BPF_STX) {
 		if (BPF_MODE(insn->code) == BPF_MEM)
-			verbose(env, "(%02x) *(%s *)(r%d %+d) = r%d\n",
+			verbose(cbs->private_data, "(%02x) *(%s *)(r%d %+d) = r%d\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg,
 				insn->off, insn->src_reg);
 		else if (BPF_MODE(insn->code) == BPF_XADD)
-			verbose(env, "(%02x) lock *(%s *)(r%d %+d) += r%d\n",
+			verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) += r%d\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->dst_reg, insn->off,
 				insn->src_reg);
 		else
-			verbose(env, "BUG_%02x\n", insn->code);
+			verbose(cbs->private_data, "BUG_%02x\n", insn->code);
 	} else if (class == BPF_ST) {
 		if (BPF_MODE(insn->code) != BPF_MEM) {
-			verbose(env, "BUG_st_%02x\n", insn->code);
+			verbose(cbs->private_data, "BUG_st_%02x\n", insn->code);
 			return;
 		}
-		verbose(env, "(%02x) *(%s *)(r%d %+d) = %d\n",
+		verbose(cbs->private_data, "(%02x) *(%s *)(r%d %+d) = %d\n",
 			insn->code,
 			bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 			insn->dst_reg,
 			insn->off, insn->imm);
 	} else if (class == BPF_LDX) {
 		if (BPF_MODE(insn->code) != BPF_MEM) {
-			verbose(env, "BUG_ldx_%02x\n", insn->code);
+			verbose(cbs->private_data, "BUG_ldx_%02x\n", insn->code);
 			return;
 		}
-		verbose(env, "(%02x) r%d = *(%s *)(r%d %+d)\n",
+		verbose(cbs->private_data, "(%02x) r%d = *(%s *)(r%d %+d)\n",
 			insn->code, insn->dst_reg,
 			bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 			insn->src_reg, insn->off);
 	} else if (class == BPF_LD) {
 		if (BPF_MODE(insn->code) == BPF_ABS) {
-			verbose(env, "(%02x) r0 = *(%s *)skb[%d]\n",
+			verbose(cbs->private_data, "(%02x) r0 = *(%s *)skb[%d]\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->imm);
 		} else if (BPF_MODE(insn->code) == BPF_IND) {
-			verbose(env, "(%02x) r0 = *(%s *)skb[r%d + %d]\n",
+			verbose(cbs->private_data, "(%02x) r0 = *(%s *)skb[r%d + %d]\n",
 				insn->code,
 				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
 				insn->src_reg, insn->imm);
@@ -212,12 +212,12 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 			if (map_ptr && !allow_ptr_leaks)
 				imm = 0;
 
-			verbose(env, "(%02x) r%d = %s\n",
+			verbose(cbs->private_data, "(%02x) r%d = %s\n",
 				insn->code, insn->dst_reg,
 				__func_imm_name(cbs, insn, imm,
 						tmp, sizeof(tmp)));
 		} else {
-			verbose(env, "BUG_ld_%02x\n", insn->code);
+			verbose(cbs->private_data, "BUG_ld_%02x\n", insn->code);
 			return;
 		}
 	} else if (class == BPF_JMP) {
@@ -227,35 +227,35 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
 			char tmp[64];
 
 			if (insn->src_reg == BPF_PSEUDO_CALL) {
-				verbose(env, "(%02x) call pc%s\n",
+				verbose(cbs->private_data, "(%02x) call pc%s\n",
 					insn->code,
 					__func_get_name(cbs, insn,
 							tmp, sizeof(tmp)));
 			} else {
 				strcpy(tmp, "unknown");
-				verbose(env, "(%02x) call %s#%d\n", insn->code,
+				verbose(cbs->private_data, "(%02x) call %s#%d\n", insn->code,
 					__func_get_name(cbs, insn,
 							tmp, sizeof(tmp)),
 					insn->imm);
 			}
 		} else if (insn->code == (BPF_JMP | BPF_JA)) {
-			verbose(env, "(%02x) goto pc%+d\n",
+			verbose(cbs->private_data, "(%02x) goto pc%+d\n",
 				insn->code, insn->off);
 		} else if (insn->code == (BPF_JMP | BPF_EXIT)) {
-			verbose(env, "(%02x) exit\n", insn->code);
+			verbose(cbs->private_data, "(%02x) exit\n", insn->code);
 		} else if (BPF_SRC(insn->code) == BPF_X) {
-			verbose(env, "(%02x) if r%d %s r%d goto pc%+d\n",
+			verbose(cbs->private_data, "(%02x) if r%d %s r%d goto pc%+d\n",
 				insn->code, insn->dst_reg,
 				bpf_jmp_string[BPF_OP(insn->code) >> 4],
 				insn->src_reg, insn->off);
 		} else {
-			verbose(env, "(%02x) if r%d %s 0x%x goto pc%+d\n",
+			verbose(cbs->private_data, "(%02x) if r%d %s 0x%x goto pc%+d\n",
 				insn->code, insn->dst_reg,
 				bpf_jmp_string[BPF_OP(insn->code) >> 4],
 				insn->imm, insn->off);
 		}
 	} else {
-		verbose(env, "(%02x) %s\n",
+		verbose(cbs->private_data, "(%02x) %s\n",
 			insn->code, bpf_class_string[class]);
 	}
 }
diff --git a/kernel/bpf/disasm.h b/kernel/bpf/disasm.h
index 266fe8ee542b..e1324a834a24 100644
--- a/kernel/bpf/disasm.h
+++ b/kernel/bpf/disasm.h
@@ -22,14 +22,12 @@
 #include <string.h>
 #endif
 
-struct bpf_verifier_env;
-
 extern const char *const bpf_alu_string[16];
 extern const char *const bpf_class_string[8];
 
 const char *func_id_name(int id);
 
-typedef __printf(2, 3) void (*bpf_insn_print_t)(struct bpf_verifier_env *env,
+typedef __printf(2, 3) void (*bpf_insn_print_t)(void *private_data,
 						const char *, ...);
 typedef const char *(*bpf_insn_revmap_call_t)(void *private_data,
 					      const struct bpf_insn *insn);
@@ -45,7 +43,6 @@ struct bpf_insn_cbs {
 };
 
 void print_bpf_insn(const struct bpf_insn_cbs *cbs,
-		    struct bpf_verifier_env *env,
 		    const struct bpf_insn *insn,
 		    bool allow_ptr_leaks);
 #endif
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e9f7c20691c1..e93a6e48641b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -168,23 +168,16 @@ struct bpf_call_arg_meta {
 
 static DEFINE_MUTEX(bpf_verifier_lock);
 
-/* log_level controls verbosity level of eBPF verifier.
- * bpf_verifier_log_write() is used to dump the verification trace to the log,
- * so the user can figure out what's wrong with the program
- */
-__printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
-					   const char *fmt, ...)
+static void log_write(struct bpf_verifier_env *env, const char *fmt,
+		      va_list args)
 {
 	struct bpf_verifer_log *log = &env->log;
 	unsigned int n;
-	va_list args;
 
 	if (!log->level || !log->ubuf || bpf_verifier_log_full(log))
 		return;
 
-	va_start(args, fmt);
 	n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
-	va_end(args);
 
 	WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
 		  "verifier log line truncated - local buffer too short\n");
@@ -197,14 +190,30 @@ __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 	else
 		log->ubuf = NULL;
 }
-EXPORT_SYMBOL_GPL(bpf_verifier_log_write);
-/* Historically bpf_verifier_log_write was called verbose, but the name was too
- * generic for symbol export. The function was renamed, but not the calls in
- * the verifier to avoid complicating backports. Hence the alias below.
+
+/* log_level controls verbosity level of eBPF verifier.
+ * bpf_verifier_log_write() is used to dump the verification trace to the log,
+ * so the user can figure out what's wrong with the program
  */
-static __printf(2, 3) void verbose(struct bpf_verifier_env *env,
-				   const char *fmt, ...)
-	__attribute__((alias("bpf_verifier_log_write")));
+__printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
+					   const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	log_write(env, fmt, args);
+	va_end(args);
+}
+EXPORT_SYMBOL_GPL(bpf_verifier_log_write);
+
+__printf(2, 3) static void verbose(void *private_data, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	log_write(private_data, fmt, args);
+	va_end(args);
+}
 
 static bool type_is_pkt_pointer(enum bpf_reg_type type)
 {
@@ -4600,10 +4609,11 @@ static int do_check(struct bpf_verifier_env *env)
 		if (env->log.level) {
 			const struct bpf_insn_cbs cbs = {
 				.cb_print	= verbose,
+				.private_data	= env,
 			};
 
 			verbose(env, "%d: ", insn_idx);
-			print_bpf_insn(&cbs, env, insn, env->allow_ptr_leaks);
+			print_bpf_insn(&cbs, insn, env->allow_ptr_leaks);
 		}
 
 		if (bpf_prog_is_dev_bound(env->prog->aux)) {