path: root/samples/bpf/tracex3_user.c
diff options
authorDaniel Borkmann <daniel@iogearbox.net>2016-11-26 01:28:09 +0100
committerDavid S. Miller <davem@davemloft.net>2016-11-27 20:38:47 -0500
commite00c7b216f34444252f3771f7d4ed48d4f032636 (patch)
tree7fae6065a59905fde41a77c01c968088e526d0c4 /samples/bpf/tracex3_user.c
parenta3af5f80010625a9ffbe8edd4bae615a7516b6bc (diff)
bpf: fix multiple issues in selftest suite and samples
1) The test_lru_map and test_lru_dist fails building on my machine since the sys/resource.h header is not included. 2) test_verifier fails in one test case where we try to call an invalid function, since the verifier log output changed wrt printing function names. 3) Current selftest suite code relies on sysconf(_SC_NPROCESSORS_CONF) for retrieving the number of possible CPUs. This is broken at least in our scenario and really just doesn't work. glibc tries a number of things for retrieving _SC_NPROCESSORS_CONF. First it tries equivalent of /sys/devices/system/cpu/cpu[0-9]* | wc -l, if that fails, depending on the config, it either tries to count CPUs in /proc/cpuinfo, or returns the _SC_NPROCESSORS_ONLN value instead. If /proc/cpuinfo has some issue, it returns just 1 worst case. This oddity is nothing new [1], but semantics/behaviour seems to be settled. _SC_NPROCESSORS_ONLN will parse /sys/devices/system/cpu/online, if that fails it looks into /proc/stat for cpuX entries, and if also that fails for some reason, /proc/cpuinfo is consulted (and returning 1 if unlikely all breaks down). While that might match num_possible_cpus() from the kernel in some cases, it's really not guaranteed with CPU hotplugging, and can result in a buffer overflow since the array in user space could have too few number of slots, and on perpcu map lookup, the kernel will write beyond that memory of the value buffer. William Tu reported such mismatches: [...] The fact that sysconf(_SC_NPROCESSORS_CONF) != num_possible_cpu() happens when CPU hotadd is enabled. For example, in Fusion when setting vcpu.hotadd = "TRUE" or in KVM, setting ./qemu-system-x86_64 -smp 2, maxcpus=4 ... the num_possible_cpu() will be 4 and sysconf() will be 2 [2]. [...] Documentation/cputopology.txt says /sys/devices/system/cpu/possible outputs cpu_possible_mask. That is the same as in num_possible_cpus(), so first step would be to fix the _SC_NPROCESSORS_CONF calls with our own implementation. Later, we could add support to bpf(2) for passing a mask via CPU_SET(3), for example, to just select a subset of CPUs. BPF samples code needs this fix as well (at least so that people stop copying this). Thus, define bpf_num_possible_cpus() once in selftests and import it from there for the sample code to avoid duplicating it. The remaining sysconf(_SC_NPROCESSORS_CONF) in samples are unrelated. After all three issues are fixed, the test suite runs fine again: # make run_tests | grep self selftests: test_verifier [PASS] selftests: test_maps [PASS] selftests: test_lru_map [PASS] selftests: test_kmod.sh [PASS] [1] https://www.sourceware.org/ml/libc-alpha/2011-06/msg00079.html [2] https://www.mail-archive.com/netdev@vger.kernel.org/msg121183.html Fixes: 3059303f59cf ("samples/bpf: update tracex[23] examples to use per-cpu maps") Fixes: 86af8b4191d2 ("Add sample for adding simple drop program to link") Fixes: df570f577231 ("samples/bpf: unit test for BPF_MAP_TYPE_PERCPU_ARRAY") Fixes: e15596717948 ("samples/bpf: unit test for BPF_MAP_TYPE_PERCPU_HASH") Fixes: ebb676daa1a3 ("bpf: Print function name in addition to function id") Fixes: 5db58faf989f ("bpf: Add tests for the LRU bpf_htab") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: William Tu <u9012063@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'samples/bpf/tracex3_user.c')
1 files changed, 4 insertions, 2 deletions
diff --git a/samples/bpf/tracex3_user.c b/samples/bpf/tracex3_user.c
index 48716f7f0d8b..d0851cb4fa8d 100644
--- a/samples/bpf/tracex3_user.c
+++ b/samples/bpf/tracex3_user.c
@@ -11,8 +11,10 @@
#include <stdbool.h>
#include <string.h>
#include <linux/bpf.h>
#include "libbpf.h"
#include "bpf_load.h"
+#include "bpf_util.h"
#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
@@ -20,7 +22,7 @@
static void clear_stats(int fd)
- unsigned int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
+ unsigned int nr_cpus = bpf_num_possible_cpus();
__u64 values[nr_cpus];
__u32 key;
@@ -77,7 +79,7 @@ static void print_banner(void)
static void print_hist(int fd)
- unsigned int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
+ unsigned int nr_cpus = bpf_num_possible_cpus();
__u64 total_events = 0;
long values[nr_cpus];
__u64 max_cnt = 0;