[PATCH 1/2] selftests/bpf: ksym_search won't check symbols exists

[PATCH 1/2] selftests/bpf: ksym_search won't check symbols exists

[Daniel T. Lee]

Currently, ksym_search located at trace_helpers won't check symbols are
existing or not.

In ksym_search, when symbol is not found, it will return &syms[0](_stext).
But when the kernel symbols are not loaded, it will return NULL, which is
not a desired action.

This commit will add verification logic whether symbols are loaded prior
to the symbol search.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
---
 tools/testing/selftests/bpf/trace_helpers.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 4cdb63bf0521..9a9fc6c9b70b 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -52,6 +52,10 @@ struct ksym *ksym_search(long key)
 	int start = 0, end = sym_cnt;
 	int result;
 
+	/* kallsyms not loaded. return NULL */
+	if (sym_cnt <= 0)
+		return NULL;
+
 	while (start < end) {
 		size_t mid = start + (end - start) / 2;
 
-- 
2.17.1

[PATCH 2/2] samples/bpf: add NULL check for ksym_search

[Daniel T. Lee]

Since, ksym_search added with verification logic for symbols existence,
it could return NULL when the kernel symbols are not loaded.

This commit will add NULL check logic after ksym_search.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
---
 samples/bpf/offwaketime_user.c | 5 +++++
 samples/bpf/sampleip_user.c    | 5 +++++
 samples/bpf/trace_event_user.c | 5 +++++
 3 files changed, 15 insertions(+)

diff --git a/samples/bpf/offwaketime_user.c b/samples/bpf/offwaketime_user.c
index f06063af9fcb..52e29467a509 100644
--- a/samples/bpf/offwaketime_user.c
+++ b/samples/bpf/offwaketime_user.c
@@ -28,6 +28,11 @@ static void print_ksym(__u64 addr)
 	if (!addr)
 		return;
 	sym = ksym_search(addr);
+	if (!sym){
+		printf("ksym not found. Is kallsyms loaded?\n");
+		return;
+	}
+
 	if (PRINT_RAW_ADDR)
 		printf("%s/%llx;", sym->name, addr);
 	else
diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
index 216c7ecbbbe9..23b90a45c802 100644
--- a/samples/bpf/sampleip_user.c
+++ b/samples/bpf/sampleip_user.c
@@ -109,6 +109,11 @@ static void print_ip_map(int fd)
 	for (i = 0; i < max; i++) {
 		if (counts[i].ip > PAGE_OFFSET) {
 			sym = ksym_search(counts[i].ip);
+			if (!sym) {
+				printf("ksym not found. Is kallsyms loaded?\n");
+				continue;
+			}
+
 			printf("0x%-17llx %-32s %u\n", counts[i].ip, sym->name,
 			       counts[i].count);
 		} else {
diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
index d08046ab81f0..bc8e6afdae6d 100644
--- a/samples/bpf/trace_event_user.c
+++ b/samples/bpf/trace_event_user.c
@@ -34,6 +34,11 @@ static void print_ksym(__u64 addr)
 	if (!addr)
 		return;
 	sym = ksym_search(addr);
+	if (!sym){
+		printf("ksym not found. Is kallsyms loaded?\n");
+		return;
+	}
+
 	printf("%s;", sym->name);
 	if (!strcmp(sym->name, "sys_read"))
 		sys_read_seen = true;
-- 
2.17.1

Re: [PATCH 2/2] samples/bpf: add NULL check for ksym_search

[Daniel Borkmann]

On 03/15/2019 07:42 AM, Daniel T. Lee wrote:
> Since, ksym_search added with verification logic for symbols existence,
> it could return NULL when the kernel symbols are not loaded.
> 
> This commit will add NULL check logic after ksym_search.
> 
> Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> ---
>  samples/bpf/offwaketime_user.c | 5 +++++
>  samples/bpf/sampleip_user.c    | 5 +++++
>  samples/bpf/trace_event_user.c | 5 +++++
>  3 files changed, 15 insertions(+)

This would also need fixing to check for NULL in:

tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c

> diff --git a/samples/bpf/offwaketime_user.c b/samples/bpf/offwaketime_user.c
> index f06063af9fcb..52e29467a509 100644
> --- a/samples/bpf/offwaketime_user.c
> +++ b/samples/bpf/offwaketime_user.c
> @@ -28,6 +28,11 @@ static void print_ksym(__u64 addr)
>  	if (!addr)
>  		return;
>  	sym = ksym_search(addr);
> +	if (!sym){
> +		printf("ksym not found. Is kallsyms loaded?\n");
> +		return;
> +	}
> +
>  	if (PRINT_RAW_ADDR)
>  		printf("%s/%llx;", sym->name, addr);
>  	else
> diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
> index 216c7ecbbbe9..23b90a45c802 100644
> --- a/samples/bpf/sampleip_user.c
> +++ b/samples/bpf/sampleip_user.c
> @@ -109,6 +109,11 @@ static void print_ip_map(int fd)
>  	for (i = 0; i < max; i++) {
>  		if (counts[i].ip > PAGE_OFFSET) {
>  			sym = ksym_search(counts[i].ip);
> +			if (!sym) {
> +				printf("ksym not found. Is kallsyms loaded?\n");
> +				continue;
> +			}
> +
>  			printf("0x%-17llx %-32s %u\n", counts[i].ip, sym->name,
>  			       counts[i].count);
>  		} else {
> diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
> index d08046ab81f0..bc8e6afdae6d 100644
> --- a/samples/bpf/trace_event_user.c
> +++ b/samples/bpf/trace_event_user.c
> @@ -34,6 +34,11 @@ static void print_ksym(__u64 addr)
>  	if (!addr)
>  		return;
>  	sym = ksym_search(addr);
> +	if (!sym){
> +		printf("ksym not found. Is kallsyms loaded?\n");
> +		return;
> +	}
> +
>  	printf("%s;", sym->name);
>  	if (!strcmp(sym->name, "sys_read"))
>  		sys_read_seen = true;
>