6.4-stable review patch. If anyone has any objections, please let me know.
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From: Daniel T. Lee danieltimlee@gmail.com
[ Upstream commit d93a7cf6ca2cfcd7de5d06f753ce8d5e863316ac ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- samples/bpf/tracex6_kern.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/samples/bpf/tracex6_kern.c b/samples/bpf/tracex6_kern.c index acad5712d8b4f..fd602c2774b8b 100644 --- a/samples/bpf/tracex6_kern.c +++ b/samples/bpf/tracex6_kern.c @@ -2,6 +2,8 @@ #include <linux/version.h> #include <uapi/linux/bpf.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); @@ -45,13 +47,24 @@ 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;