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authorDaniel T. Lee <danieltimlee@gmail.com>2023-08-18 12:01:17 +0300
committerAlexei Starovoitov <ast@kernel.org>2023-08-22 01:39:09 +0300
commitd93a7cf6ca2cfcd7de5d06f753ce8d5e863316ac (patch)
tree327fa6cea4d2b66d51367834b8a357955a08c069 /samples
parent92632115fb57ff9e368f256913e96d6fd5abf5ab (diff)
downloadlinux-d93a7cf6ca2cfcd7de5d06f753ce8d5e863316ac.tar.xz
samples/bpf: fix broken map lookup probe
In the commit 7c4cd051add3 ("bpf: Fix syscall's stackmap lookup potential deadlock"), a potential deadlock issue was addressed, which resulted in *_map_lookup_elem not triggering BPF programs. (prior to lookup, bpf_disable_instrumentation() is used) To resolve the broken map lookup probe using "htab_map_lookup_elem", this commit introduces an alternative approach. Instead, it utilize "bpf_map_copy_value" and apply a filter specifically for the hash table with map_type. Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com> Fixes: 7c4cd051add3 ("bpf: Fix syscall's stackmap lookup potential deadlock") Link: https://lore.kernel.org/r/20230818090119.477441-8-danieltimlee@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'samples')
-rw-r--r--samples/bpf/tracex6.bpf.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/samples/bpf/tracex6.bpf.c b/samples/bpf/tracex6.bpf.c
index 6ad82e68f998..9b23b4737cfb 100644
--- a/samples/bpf/tracex6.bpf.c
+++ b/samples/bpf/tracex6.bpf.c
@@ -1,6 +1,8 @@
#include "vmlinux.h"
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
struct {
__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
@@ -44,13 +46,24 @@ int bpf_prog1(struct pt_regs *ctx)
return 0;
}
-SEC("kprobe/htab_map_lookup_elem")
-int bpf_prog2(struct pt_regs *ctx)
+/*
+ * Since *_map_lookup_elem can't be expected to trigger bpf programs
+ * due to potential deadlocks (bpf_disable_instrumentation), this bpf
+ * program will be attached to bpf_map_copy_value (which is called
+ * from map_lookup_elem) and will only filter the hashtable type.
+ */
+SEC("kprobe/bpf_map_copy_value")
+int BPF_KPROBE(bpf_prog2, struct bpf_map *map)
{
u32 key = bpf_get_smp_processor_id();
struct bpf_perf_event_value *val, buf;
+ enum bpf_map_type type;
int error;
+ type = BPF_CORE_READ(map, map_type);
+ if (type != BPF_MAP_TYPE_HASH)
+ return 0;
+
error = bpf_perf_event_read_value(&counters, key, &buf, sizeof(buf));
if (error)
return 0;