[PATCH v2 bpf-next 0/4] bpf: Support ksym detection in light skeleton.

[PATCH v2 bpf-next 0/4] bpf: Support ksym detection in light skeleton.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

v1->v2: update denylist on s390

Patch 1: Cleanup internal libbpf names.
Patch 2: Teach the verifier that rdonly_mem != NULL.
Patch 3: Fix gen_loader to support ksym detection.
Patch 4: Selftest and update denylist.

Alexei Starovoitov (4):
  libbpf: Rename RELO_EXTERN_VAR/FUNC.
  bpf: Teach the verifier to recognize rdonly_mem as not null.
  libbpf: Support kfunc detection in light skeleton.
  selftests/bpf: Add light skeleton test for kfunc detection.

 kernel/bpf/verifier.c                         | 14 ++++---
 tools/lib/bpf/bpf_gen_internal.h              |  4 +-
 tools/lib/bpf/gen_loader.c                    | 38 +++++++++----------
 tools/lib/bpf/libbpf.c                        | 25 ++++++------
 tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
 .../selftests/bpf/progs/test_ksyms_weak.c     | 15 ++++++++
 6 files changed, 61 insertions(+), 36 deletions(-)

-- 
2.34.1

[PATCH v2 bpf-next 1/4] libbpf: Rename RELO_EXTERN_VAR/FUNC.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

RELO_EXTERN_VAR/FUNC names are not correct anymore. RELO_EXTERN_VAR represent
ksym symbol in ld_imm64 insn. It can point to kernel variable or kfunc.
Rename RELO_EXTERN_VAR->RELO_EXTERN_LD64 and RELO_EXTERN_FUNC->RELO_EXTERN_CALL
to match what they actually represent.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/lib/bpf/libbpf.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 149864ea88d1..f8131f963803 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -315,8 +315,8 @@ enum reloc_type {
 	RELO_LD64,
 	RELO_CALL,
 	RELO_DATA,
-	RELO_EXTERN_VAR,
-	RELO_EXTERN_FUNC,
+	RELO_EXTERN_LD64,
+	RELO_EXTERN_CALL,
 	RELO_SUBPROG_ADDR,
 	RELO_CORE,
 };
@@ -4009,9 +4009,9 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 		pr_debug("prog '%s': found extern #%d '%s' (sym %d) for insn #%u\n",
 			 prog->name, i, ext->name, ext->sym_idx, insn_idx);
 		if (insn->code == (BPF_JMP | BPF_CALL))
-			reloc_desc->type = RELO_EXTERN_FUNC;
+			reloc_desc->type = RELO_EXTERN_CALL;
 		else
-			reloc_desc->type = RELO_EXTERN_VAR;
+			reloc_desc->type = RELO_EXTERN_LD64;
 		reloc_desc->insn_idx = insn_idx;
 		reloc_desc->sym_off = i; /* sym_off stores extern index */
 		return 0;
@@ -5855,7 +5855,7 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 						   relo->map_idx, map);
 			}
 			break;
-		case RELO_EXTERN_VAR:
+		case RELO_EXTERN_LD64:
 			ext = &obj->externs[relo->sym_off];
 			if (ext->type == EXT_KCFG) {
 				if (obj->gen_loader) {
@@ -5877,7 +5877,7 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 				}
 			}
 			break;
-		case RELO_EXTERN_FUNC:
+		case RELO_EXTERN_CALL:
 			ext = &obj->externs[relo->sym_off];
 			insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
 			if (ext->is_set) {
@@ -6115,7 +6115,7 @@ bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
 			continue;
 
 		relo = find_prog_insn_relo(prog, insn_idx);
-		if (relo && relo->type == RELO_EXTERN_FUNC)
+		if (relo && relo->type == RELO_EXTERN_CALL)
 			/* kfunc relocations will be handled later
 			 * in bpf_object__relocate_data()
 			 */
@@ -7072,14 +7072,14 @@ static int bpf_program_record_relos(struct bpf_program *prog)
 		struct extern_desc *ext = &obj->externs[relo->sym_off];
 
 		switch (relo->type) {
-		case RELO_EXTERN_VAR:
+		case RELO_EXTERN_LD64:
 			if (ext->type != EXT_KSYM)
 				continue;
 			bpf_gen__record_extern(obj->gen_loader, ext->name,
 					       ext->is_weak, !ext->ksym.type_id,
 					       BTF_KIND_VAR, relo->insn_idx);
 			break;
-		case RELO_EXTERN_FUNC:
+		case RELO_EXTERN_CALL:
 			bpf_gen__record_extern(obj->gen_loader, ext->name,
 					       ext->is_weak, false, BTF_KIND_FUNC,
 					       relo->insn_idx);
-- 
2.34.1

Re: [PATCH v2 bpf-next 1/4] libbpf: Rename RELO_EXTERN_VAR/FUNC.

[David Vernet]

On Tue, Mar 21, 2023 at 01:38:51PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> RELO_EXTERN_VAR/FUNC names are not correct anymore. RELO_EXTERN_VAR represent
> ksym symbol in ld_imm64 insn. It can point to kernel variable or kfunc.
> Rename RELO_EXTERN_VAR->RELO_EXTERN_LD64 and RELO_EXTERN_FUNC->RELO_EXTERN_CALL
> to match what they actually represent.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Acked-by: David Vernet <void@manifault.com>

[PATCH v2 bpf-next 2/4] bpf: Teach the verifier to recognize rdonly_mem as not null.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Teach the verifier to recognize PTR_TO_MEM | MEM_RDONLY as not NULL
otherwise if (!bpf_ksym_exists(known_kfunc)) doesn't go through
dead code elimination.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8bc44f5dc5b6..5693e4a92752 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -486,8 +486,17 @@ static bool type_is_sk_pointer(enum bpf_reg_type type)
 		type == PTR_TO_XDP_SOCK;
 }
 
+static bool type_may_be_null(u32 type)
+{
+	return type & PTR_MAYBE_NULL;
+}
+
 static bool reg_type_not_null(enum bpf_reg_type type)
 {
+	if (type_may_be_null(type))
+		return false;
+
+	type = base_type(type);
 	return type == PTR_TO_SOCKET ||
 		type == PTR_TO_TCP_SOCK ||
 		type == PTR_TO_MAP_VALUE ||
@@ -531,11 +540,6 @@ static bool type_is_rdonly_mem(u32 type)
 	return type & MEM_RDONLY;
 }
 
-static bool type_may_be_null(u32 type)
-{
-	return type & PTR_MAYBE_NULL;
-}
-
 static bool is_acquire_function(enum bpf_func_id func_id,
 				const struct bpf_map *map)
 {
-- 
2.34.1

Re: [PATCH v2 bpf-next 2/4] bpf: Teach the verifier to recognize rdonly_mem as not null.

[David Vernet]

On Tue, Mar 21, 2023 at 01:38:52PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> Teach the verifier to recognize PTR_TO_MEM | MEM_RDONLY as not NULL
> otherwise if (!bpf_ksym_exists(known_kfunc)) doesn't go through
> dead code elimination.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Acked-by: David Vernet <void@manifault.com>

[PATCH v2 bpf-next 3/4] libbpf: Support kfunc detection in light skeleton.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Teach gen_loader to find {btf_id, btf_obj_fd} of kernel variables and kfuncs
and populate corresponding ld_imm64 and bpf_call insns.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/lib/bpf/bpf_gen_internal.h |  4 +++-
 tools/lib/bpf/gen_loader.c       | 38 ++++++++++++++++----------------
 tools/lib/bpf/libbpf.c           |  7 ++++--
 3 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
index 223308931d55..fdf44403ff36 100644
--- a/tools/lib/bpf/bpf_gen_internal.h
+++ b/tools/lib/bpf/bpf_gen_internal.h
@@ -11,6 +11,7 @@ struct ksym_relo_desc {
 	int insn_idx;
 	bool is_weak;
 	bool is_typeless;
+	bool is_ld64;
 };
 
 struct ksym_desc {
@@ -24,6 +25,7 @@ struct ksym_desc {
 		bool typeless;
 	};
 	int insn;
+	bool is_ld64;
 };
 
 struct bpf_gen {
@@ -65,7 +67,7 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *value, __u
 void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx);
 void bpf_gen__record_attach_target(struct bpf_gen *gen, const char *name, enum bpf_attach_type type);
 void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
-			    bool is_typeless, int kind, int insn_idx);
+			    bool is_typeless, bool is_ld64, int kind, int insn_idx);
 void bpf_gen__record_relo_core(struct bpf_gen *gen, const struct bpf_core_relo *core_relo);
 void bpf_gen__populate_outer_map(struct bpf_gen *gen, int outer_map_idx, int key, int inner_map_idx);
 
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index b74c82bb831e..83e8e3bfd8ff 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -560,7 +560,7 @@ static void emit_find_attach_target(struct bpf_gen *gen)
 }
 
 void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
-			    bool is_typeless, int kind, int insn_idx)
+			    bool is_typeless, bool is_ld64, int kind, int insn_idx)
 {
 	struct ksym_relo_desc *relo;
 
@@ -574,6 +574,7 @@ void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
 	relo->name = name;
 	relo->is_weak = is_weak;
 	relo->is_typeless = is_typeless;
+	relo->is_ld64 = is_ld64;
 	relo->kind = kind;
 	relo->insn_idx = insn_idx;
 	gen->relo_cnt++;
@@ -586,9 +587,11 @@ static struct ksym_desc *get_ksym_desc(struct bpf_gen *gen, struct ksym_relo_des
 	int i;
 
 	for (i = 0; i < gen->nr_ksyms; i++) {
-		if (!strcmp(gen->ksyms[i].name, relo->name)) {
-			gen->ksyms[i].ref++;
-			return &gen->ksyms[i];
+		kdesc = &gen->ksyms[i];
+		if (kdesc->kind == relo->kind && kdesc->is_ld64 == relo->is_ld64 &&
+		    !strcmp(kdesc->name, relo->name)) {
+			kdesc->ref++;
+			return kdesc;
 		}
 	}
 	kdesc = libbpf_reallocarray(gen->ksyms, gen->nr_ksyms + 1, sizeof(*kdesc));
@@ -603,6 +606,7 @@ static struct ksym_desc *get_ksym_desc(struct bpf_gen *gen, struct ksym_relo_des
 	kdesc->ref = 1;
 	kdesc->off = 0;
 	kdesc->insn = 0;
+	kdesc->is_ld64 = relo->is_ld64;
 	return kdesc;
 }
 
@@ -864,23 +868,17 @@ static void emit_relo(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insn
 {
 	int insn;
 
-	pr_debug("gen: emit_relo (%d): %s at %d\n", relo->kind, relo->name, relo->insn_idx);
+	pr_debug("gen: emit_relo (%d): %s at %d %s\n",
+		 relo->kind, relo->name, relo->insn_idx, relo->is_ld64 ? "ld64" : "call");
 	insn = insns + sizeof(struct bpf_insn) * relo->insn_idx;
 	emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_8, BPF_PSEUDO_MAP_IDX_VALUE, 0, 0, 0, insn));
-	switch (relo->kind) {
-	case BTF_KIND_VAR:
+	if (relo->is_ld64) {
 		if (relo->is_typeless)
 			emit_relo_ksym_typeless(gen, relo, insn);
 		else
 			emit_relo_ksym_btf(gen, relo, insn);
-		break;
-	case BTF_KIND_FUNC:
+	} else {
 		emit_relo_kfunc_btf(gen, relo, insn);
-		break;
-	default:
-		pr_warn("Unknown relocation kind '%d'\n", relo->kind);
-		gen->error = -EDOM;
-		return;
 	}
 }
 
@@ -903,18 +901,20 @@ static void cleanup_core_relo(struct bpf_gen *gen)
 
 static void cleanup_relos(struct bpf_gen *gen, int insns)
 {
+	struct ksym_desc *kdesc;
 	int i, insn;
 
 	for (i = 0; i < gen->nr_ksyms; i++) {
+		kdesc = &gen->ksyms[i];
 		/* only close fds for typed ksyms and kfuncs */
-		if (gen->ksyms[i].kind == BTF_KIND_VAR && !gen->ksyms[i].typeless) {
+		if (kdesc->is_ld64 && !kdesc->typeless) {
 			/* close fd recorded in insn[insn_idx + 1].imm */
-			insn = gen->ksyms[i].insn;
+			insn = kdesc->insn;
 			insn += sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm);
 			emit_sys_close_blob(gen, insn);
-		} else if (gen->ksyms[i].kind == BTF_KIND_FUNC) {
-			emit_sys_close_blob(gen, blob_fd_array_off(gen, gen->ksyms[i].off));
-			if (gen->ksyms[i].off < MAX_FD_ARRAY_SZ)
+		} else if (!kdesc->is_ld64) {
+			emit_sys_close_blob(gen, blob_fd_array_off(gen, kdesc->off));
+			if (kdesc->off < MAX_FD_ARRAY_SZ)
 				gen->nr_fd_array--;
 		}
 	}
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f8131f963803..5d32aa8ea38a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7070,18 +7070,21 @@ static int bpf_program_record_relos(struct bpf_program *prog)
 	for (i = 0; i < prog->nr_reloc; i++) {
 		struct reloc_desc *relo = &prog->reloc_desc[i];
 		struct extern_desc *ext = &obj->externs[relo->sym_off];
+		int kind;
 
 		switch (relo->type) {
 		case RELO_EXTERN_LD64:
 			if (ext->type != EXT_KSYM)
 				continue;
+			kind = btf_is_var(btf__type_by_id(obj->btf, ext->btf_id)) ?
+				BTF_KIND_VAR : BTF_KIND_FUNC;
 			bpf_gen__record_extern(obj->gen_loader, ext->name,
 					       ext->is_weak, !ext->ksym.type_id,
-					       BTF_KIND_VAR, relo->insn_idx);
+					       true, kind, relo->insn_idx);
 			break;
 		case RELO_EXTERN_CALL:
 			bpf_gen__record_extern(obj->gen_loader, ext->name,
-					       ext->is_weak, false, BTF_KIND_FUNC,
+					       ext->is_weak, false, false, BTF_KIND_FUNC,
 					       relo->insn_idx);
 			break;
 		case RELO_CORE: {
-- 
2.34.1

[PATCH v2 bpf-next 4/4] selftests/bpf: Add light skeleton test for kfunc detection.

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

Add light skeleton test for kfunc detection and denylist it for s390.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/testing/selftests/bpf/DENYLIST.s390x        |  1 +
 .../testing/selftests/bpf/progs/test_ksyms_weak.c | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
index 34cb8b2de8ca..c7463f3ec3c0 100644
--- a/tools/testing/selftests/bpf/DENYLIST.s390x
+++ b/tools/testing/selftests/bpf/DENYLIST.s390x
@@ -11,6 +11,7 @@ get_stack_raw_tp                         # user_stack corrupted user stack
 iters/testmod_seq*                       # s390x doesn't support kfuncs in modules yet
 kprobe_multi_bench_attach                # bpf_program__attach_kprobe_multi_opts unexpected error: -95
 kprobe_multi_test                        # relies on fentry
+ksyms_btf/weak_ksyms*                    # test_ksyms_weak__open_and_load unexpected error: -22                        (kfunc)
 ksyms_module                             # test_ksyms_module__open_and_load unexpected error: -9                       (?)
 ksyms_module_libbpf                      # JIT does not support calling kernel function                                (kfunc)
 ksyms_module_lskel                       # test_ksyms_module_lskel__open_and_load unexpected error: -9                 (?)
diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_weak.c b/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
index 7003eef0c192..d00268c91e19 100644
--- a/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
+++ b/tools/testing/selftests/bpf/progs/test_ksyms_weak.c
@@ -20,6 +20,8 @@ __u64 out__non_existent_typed = -1;
 /* test existing weak symbols can be resolved. */
 extern const struct rq runqueues __ksym __weak; /* typed */
 extern const void bpf_prog_active __ksym __weak; /* typeless */
+struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym __weak;
+void bpf_testmod_test_mod_kfunc(int i) __ksym __weak;
 
 
 /* non-existent weak symbols. */
@@ -29,6 +31,7 @@ extern const void bpf_link_fops1 __ksym __weak;
 
 /* typed symbols, default to zero. */
 extern const int bpf_link_fops2 __ksym __weak;
+void invalid_kfunc(void) __ksym __weak;
 
 SEC("raw_tp/sys_enter")
 int pass_handler(const void *ctx)
@@ -50,6 +53,18 @@ int pass_handler(const void *ctx)
 	if (&bpf_link_fops2) /* can't happen */
 		out__non_existent_typed = (__u64)bpf_per_cpu_ptr(&bpf_link_fops2, 0);
 
+	if (!bpf_ksym_exists(bpf_task_acquire))
+		/* dead code won't be seen by the verifier */
+		bpf_task_acquire(0);
+
+	if (!bpf_ksym_exists(bpf_testmod_test_mod_kfunc))
+		/* dead code won't be seen by the verifier */
+		bpf_testmod_test_mod_kfunc(0);
+
+	if (bpf_ksym_exists(invalid_kfunc))
+		/* dead code won't be seen by the verifier */
+		invalid_kfunc();
+
 	return 0;
 }
 
-- 
2.34.1

Re: [PATCH v2 bpf-next 0/4] bpf: Support ksym detection in light skeleton.

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Tue, 21 Mar 2023 13:38:50 -0700 you wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> v1->v2: update denylist on s390
> 
> Patch 1: Cleanup internal libbpf names.
> Patch 2: Teach the verifier that rdonly_mem != NULL.
> Patch 3: Fix gen_loader to support ksym detection.
> Patch 4: Selftest and update denylist.
> 
> [...]

Here is the summary with links:
  - [v2,bpf-next,1/4] libbpf: Rename RELO_EXTERN_VAR/FUNC.
    https://git.kernel.org/bpf/bpf-next/c/a18f721415b4
  - [v2,bpf-next,2/4] bpf: Teach the verifier to recognize rdonly_mem as not null.
    https://git.kernel.org/bpf/bpf-next/c/1057d2994596
  - [v2,bpf-next,3/4] libbpf: Support kfunc detection in light skeleton.
    https://git.kernel.org/bpf/bpf-next/c/708cdc5706a4
  - [v2,bpf-next,4/4] selftests/bpf: Add light skeleton test for kfunc detection.
    https://git.kernel.org/bpf/bpf-next/c/3b2ec2140fa2

You are awesome, thank you!
-- 
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