[PATCH 2/7] bpf: Enable BPF_TRAMP_F_IP_ARG for trampolines with call_get_func_ip

Jiri Olsa
2021-07-07T19:46:41Z

Enabling BPF_TRAMP_F_IP_ARG for trampolines that actually need it.

The BPF_TRAMP_F_IP_ARG adds extra 3 instructions to trampoline code
and is used only by programs with bpf_get_func_ip helper, which is
added in following patch and sets call_get_func_ip bit.

This patch ensures that BPF_TRAMP_F_IP_ARG flag is used only for
trampolines that have programs with call_get_func_ip set.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/filter.h | 3 ++-
kernel/bpf/trampoline.c | 12 +++++++++---
2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 472f97074da0..ba36989f711a 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -559,7 +559,8 @@ struct bpf_prog {
kprobe_override:1, /* Do we override a kprobe? */
has_callchain_buf:1, /* callchain buffer allocated? */
enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
- call_get_stack:1; /* Do we call bpf_get_stack() or bpf_get_stackid() */
+ call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */
+ call_get_func_ip:1; /* Do we call get_func_ip() */
enum bpf_prog_type type; /* Type of BPF program */
enum bpf_attach_type expected_attach_type; /* For some prog types */
u32 len; /* Number of filter blocks */
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 28a3630c48ee..b2535acfe9db 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -172,7 +172,7 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
}

static struct bpf_tramp_progs *
-bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
+bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
{
const struct bpf_prog_aux *aux;
struct bpf_tramp_progs *tprogs;
@@ -189,8 +189,10 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
*total += tr->progs_cnt[kind];
progs = tprogs[kind].progs;

- hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
+ hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist) {
+ *ip_arg |= aux->prog->call_get_func_ip;
*progs++ = aux->prog;
+ }
}
return tprogs;
}
@@ -333,9 +335,10 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
struct bpf_tramp_image *im;
struct bpf_tramp_progs *tprogs;
u32 flags = BPF_TRAMP_F_RESTORE_REGS;
+ bool ip_arg = false;
int err, total;

- tprogs = bpf_trampoline_get_progs(tr, &total);
+ tprogs = bpf_trampoline_get_progs(tr, &total, &ip_arg);
if (IS_ERR(tprogs))
return PTR_ERR(tprogs);

@@ -357,6 +360,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

+ if (ip_arg)
+ flags |= BPF_TRAMP_F_IP_ARG;
+
err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
&tr->func.model, flags, tprogs,
tr->func.addr);
--
2.31.1