[PATCH bpf-next v2 1/7] bpf: Refactor trampoline update code

From: KP Singh
Date: Tue Mar 03 2020 - 20:55:41 EST

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From: KP Singh <kpsingh@xxxxxxxxxx>

As we need to introduce a third type of attachment for trampolines, the
flattened signature of arch_prepare_bpf_trampoline gets even more
complicated.

Refactor the prog and count argument to arch_prepare_bpf_trampoline to
use bpf_tramp_progs to simplify the addition and accounting for new
attachment types.

Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 31 ++++++++++---------
include/linux/bpf.h | 13 ++++++--
kernel/bpf/bpf_struct_ops.c | 12 ++++++-
kernel/bpf/trampoline.c | 62 +++++++++++++++++++++----------------
4 files changed, 73 insertions(+), 45 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9ba08e9abc09..15c7d28bc05c 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1362,12 +1362,12 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args,
}

static int invoke_bpf(const struct btf_func_model *m, u8 **pprog,
- struct bpf_prog **progs, int prog_cnt, int stack_size)
+ struct bpf_tramp_progs *tp, int stack_size)
{
u8 *prog = *pprog;
int cnt = 0, i;

- for (i = 0; i < prog_cnt; i++) {
+ for (i = 0; i < tp->nr_progs; i++) {
if (emit_call(&prog, __bpf_prog_enter, prog))
return -EINVAL;
/* remember prog start time returned by __bpf_prog_enter */
@@ -1376,17 +1376,17 @@ static int invoke_bpf(const struct btf_func_model *m, u8 **pprog,
/* arg1: lea rdi, [rbp - stack_size] */
EMIT4(0x48, 0x8D, 0x7D, -stack_size);
/* arg2: progs[i]->insnsi for interpreter */
- if (!progs[i]->jited)
+ if (!tp->progs[i]->jited)
emit_mov_imm64(&prog, BPF_REG_2,
- (long) progs[i]->insnsi >> 32,
- (u32) (long) progs[i]->insnsi);
+ (long) tp->progs[i]->insnsi >> 32,
+ (u32) (long) tp->progs[i]->insnsi);
/* call JITed bpf program or interpreter */
- if (emit_call(&prog, progs[i]->bpf_func, prog))
+ if (emit_call(&prog, tp->progs[i]->bpf_func, prog))
return -EINVAL;

/* arg1: mov rdi, progs[i] */
- emit_mov_imm64(&prog, BPF_REG_1, (long) progs[i] >> 32,
- (u32) (long) progs[i]);
+ emit_mov_imm64(&prog, BPF_REG_1, (long) tp->progs[i] >> 32,
+ (u32) (long) tp->progs[i]);
/* arg2: mov rsi, rbx <- start time in nsec */
emit_mov_reg(&prog, true, BPF_REG_2, BPF_REG_6);
if (emit_call(&prog, __bpf_prog_exit, prog))
@@ -1458,12 +1458,13 @@ static int invoke_bpf(const struct btf_func_model *m, u8 **pprog,
*/
int arch_prepare_bpf_trampoline(void *image, void *image_end,
const struct btf_func_model *m, u32 flags,
- struct bpf_prog **fentry_progs, int fentry_cnt,
- struct bpf_prog **fexit_progs, int fexit_cnt,
+ struct bpf_tramp_progs *tprogs,
void *orig_call)
{
int cnt = 0, nr_args = m->nr_args;
int stack_size = nr_args * 8;
+ struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY];
+ struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT];
u8 *prog;

/* x86-64 supports up to 6 arguments. 7+ can be added in the future */
@@ -1492,12 +1493,12 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end,

save_regs(m, &prog, nr_args, stack_size);

- if (fentry_cnt)
- if (invoke_bpf(m, &prog, fentry_progs, fentry_cnt, stack_size))
+ if (fentry->nr_progs)
+ if (invoke_bpf(m, &prog, fentry, stack_size))
return -EINVAL;

if (flags & BPF_TRAMP_F_CALL_ORIG) {
- if (fentry_cnt)
+ if (fentry->nr_progs)
restore_regs(m, &prog, nr_args, stack_size);

/* call original function */
@@ -1507,8 +1508,8 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end,
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
}

- if (fexit_cnt)
- if (invoke_bpf(m, &prog, fexit_progs, fexit_cnt, stack_size))
+ if (fexit->nr_progs)
+ if (invoke_bpf(m, &prog, fexit, stack_size))
return -EINVAL;

if (flags & BPF_TRAMP_F_RESTORE_REGS)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f13c78c6f29d..98ec10b23dbb 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -433,6 +433,16 @@ struct btf_func_model {
*/
#define BPF_TRAMP_F_SKIP_FRAME BIT(2)

+/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
+ * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2
+ */
+#define BPF_MAX_TRAMP_PROGS 40
+
+struct bpf_tramp_progs {
+ struct bpf_prog *progs[BPF_MAX_TRAMP_PROGS];
+ int nr_progs;
+};
+
/* Different use cases for BPF trampoline:
* 1. replace nop at the function entry (kprobe equivalent)
* flags = BPF_TRAMP_F_RESTORE_REGS
@@ -455,8 +465,7 @@ struct btf_func_model {
*/
int arch_prepare_bpf_trampoline(void *image, void *image_end,
const struct btf_func_model *m, u32 flags,
- struct bpf_prog **fentry_progs, int fentry_cnt,
- struct bpf_prog **fexit_progs, int fexit_cnt,
+ struct bpf_tramp_progs *tprogs,
void *orig_call);
/* these two functions are called from generated trampoline */
u64 notrace __bpf_prog_enter(void);
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c498f0fffb40..9f7e0328a644 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -320,6 +320,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
struct bpf_struct_ops_value *uvalue, *kvalue;
const struct btf_member *member;
const struct btf_type *t = st_ops->type;
+ struct bpf_tramp_progs *tprogs = NULL;
void *udata, *kdata;
int prog_fd, err = 0;
void *image;
@@ -425,10 +426,18 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
goto reset_unlock;
}

+ tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
+ if (!tprogs) {
+ err = -ENOMEM;
+ goto reset_unlock;
+ }
+
+ tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
+ tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
err = arch_prepare_bpf_trampoline(image,
st_map->image + PAGE_SIZE,
&st_ops->func_models[i], 0,
- &prog, 1, NULL, 0, NULL);
+ tprogs, NULL);
if (err < 0)
goto reset_unlock;

@@ -469,6 +478,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
memset(uvalue, 0, map->value_size);
memset(kvalue, 0, map->value_size);
unlock:
+ kfree(tprogs);
mutex_unlock(&st_map->lock);
return err;
}
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 704fa787fec0..cfe96d4cd89f 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -190,40 +190,49 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
return ret;
}

-/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
- * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2
- */
-#define BPF_MAX_TRAMP_PROGS 40
+static struct bpf_tramp_progs *
+bpf_trampoline_update_progs(struct bpf_trampoline *tr, int *total)
+{
+ struct bpf_tramp_progs *tprogs;
+ struct bpf_prog **progs;
+ struct bpf_prog_aux *aux;
+ int kind;
+
+ *total = 0;
+ tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
+ if (!tprogs)
+ return ERR_PTR(-ENOMEM);
+
+ for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
+ tprogs[kind].nr_progs = tr->progs_cnt[kind];
+ *total += tr->progs_cnt[kind];
+ progs = tprogs[kind].progs;
+
+ hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
+ *progs++ = aux->prog;
+ }
+ return tprogs;
+}

static int bpf_trampoline_update(struct bpf_trampoline *tr)
{
void *old_image = tr->image + ((tr->selector + 1) & 1) * BPF_IMAGE_SIZE/2;
void *new_image = tr->image + (tr->selector & 1) * BPF_IMAGE_SIZE/2;
- struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS];
- int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY];
- int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT];
- struct bpf_prog **progs, **fentry, **fexit;
+ struct bpf_tramp_progs *tprogs;
u32 flags = BPF_TRAMP_F_RESTORE_REGS;
- struct bpf_prog_aux *aux;
- int err;
+ int err, total;
+
+ tprogs = bpf_trampoline_update_progs(tr, &total);
+ if (IS_ERR(tprogs))
+ return PTR_ERR(tprogs);

- if (fentry_cnt + fexit_cnt == 0) {
+ if (total == 0) {
err = unregister_fentry(tr, old_image);
tr->selector = 0;
goto out;
}

- /* populate fentry progs */
- fentry = progs = progs_to_run;
- hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist)
- *progs++ = aux->prog;
-
- /* populate fexit progs */
- fexit = progs;
- hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist)
- *progs++ = aux->prog;
-
- if (fexit_cnt)
+ if (tprogs[BPF_TRAMP_FEXIT].nr_progs)
flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

/* Though the second half of trampoline page is unused a task could be
@@ -232,12 +241,11 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
* preempted task. Hence wait for tasks to voluntarily schedule or go
* to userspace.
*/
+
synchronize_rcu_tasks();

err = arch_prepare_bpf_trampoline(new_image, new_image + BPF_IMAGE_SIZE / 2,
- &tr->func.model, flags,
- fentry, fentry_cnt,
- fexit, fexit_cnt,
+ &tr->func.model, flags, tprogs,
tr->func.addr);
if (err < 0)
goto out;
@@ -252,6 +260,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
goto out;
tr->selector++;
out:
+ kfree(tprogs);
return err;
}

@@ -409,8 +418,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
int __weak
arch_prepare_bpf_trampoline(void *image, void *image_end,
const struct btf_func_model *m, u32 flags,
- struct bpf_prog **fentry_progs, int fentry_cnt,
- struct bpf_prog **fexit_progs, int fexit_cnt,
+ struct bpf_tramp_progs *tprogs,
void *orig_call)
{
return -ENOTSUPP;
--
2.20.1

Next message: KP Singh: "[PATCH bpf-next v2 4/7] bpf: Attachment verification for BPF_MODIFY_RETURN"
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Next in thread: Andrii Nakryiko: "Re: [PATCH bpf-next v2 1/7] bpf: Refactor trampoline update code"
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