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authorPeter Zijlstra <peterz@infradead.org>2022-11-03 15:00:14 +0300
committerDaniel Borkmann <daniel@iogearbox.net>2022-11-05 01:13:57 +0300
commitc86df29d11dfba27c0a1f5039cd6fe387fbf4239 (patch)
tree3e3bde30f24960b1459df5114c9214336af0f71a /kernel
parent18acb7fac22ff7b36c7ea5a76b12996e7b7dbaba (diff)
downloadlinux-c86df29d11dfba27c0a1f5039cd6fe387fbf4239.tar.xz
bpf: Convert BPF_DISPATCHER to use static_call() (not ftrace)
The dispatcher function is currently abusing the ftrace __fentry__ call location for its own purposes -- this obviously gives trouble when the dispatcher and ftrace are both in use. A previous solution tried using __attribute__((patchable_function_entry())) which works, except it is GCC-8+ only, breaking the build on the earlier still supported compilers. Instead use static_call() -- which has its own annotations and does not conflict with ftrace -- to rewrite the dispatch function. By using: return static_call()(ctx, insni, bpf_func) you get a perfect forwarding tail call as function body (iow a single jmp instruction). By having the default static_call() target be bpf_dispatcher_nop_func() it retains the default behaviour (an indirect call to the argument function). Only once a dispatcher program is attached is the target rewritten to directly call the JIT'ed image. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Björn Töpel <bjorn@kernel.org> Tested-by: Jiri Olsa <jolsa@kernel.org> Acked-by: Björn Töpel <bjorn@kernel.org> Acked-by: Jiri Olsa <jolsa@kernel.org> Link: https://lkml.kernel.org/r/Y1/oBlK0yFk5c/Im@hirez.programming.kicks-ass.net Link: https://lore.kernel.org/bpf/20221103120647.796772565@infradead.org
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/dispatcher.c22
1 files changed, 8 insertions, 14 deletions
diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
index fa64b80b8bca..7dfb8d0d5202 100644
--- a/kernel/bpf/dispatcher.c
+++ b/kernel/bpf/dispatcher.c
@@ -4,6 +4,7 @@
#include <linux/hash.h>
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/static_call.h>
/* The BPF dispatcher is a multiway branch code generator. The
* dispatcher is a mechanism to avoid the performance penalty of an
@@ -104,17 +105,11 @@ static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image, void *b
static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
{
- void *old, *new, *tmp;
- u32 noff;
- int err;
-
- if (!prev_num_progs) {
- old = NULL;
- noff = 0;
- } else {
- old = d->image + d->image_off;
+ void *new, *tmp;
+ u32 noff = 0;
+
+ if (prev_num_progs)
noff = d->image_off ^ (PAGE_SIZE / 2);
- }
new = d->num_progs ? d->image + noff : NULL;
tmp = d->num_progs ? d->rw_image + noff : NULL;
@@ -128,11 +123,10 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
return;
}
- err = bpf_arch_text_poke(d->func, BPF_MOD_JUMP, old, new);
- if (err || !new)
- return;
+ __BPF_DISPATCHER_UPDATE(d, new ?: &bpf_dispatcher_nop_func);
- d->image_off = noff;
+ if (new)
+ d->image_off = noff;
}
void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,