netdev - [PATCH bpf-next 3/3] tools/bpftool: strip away modifiers from global variables

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Date:   Tue, 30 Jun 2020 23:45:26 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>,
        Anton Protopopov <a.s.protopopov@...il.com>
Subject: [PATCH bpf-next 3/3] tools/bpftool: strip away modifiers from global variables

Reliably remove all the type modifiers from global variable definitions,
including cases of inner field const modifiers and arrays of const values.

Also modify one of selftests to ensure that const volatile struct doesn't
prevent user-space from modifying .rodata variable.

Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/bpf/bpftool/gen.c                           | 13 ++++---------
 tools/testing/selftests/bpf/prog_tests/skeleton.c |  6 +++---
 tools/testing/selftests/bpf/progs/test_skeleton.c |  6 ++++--
 3 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 10de76b296ba..2a13114896c2 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -88,7 +88,7 @@ static const char *get_map_ident(const struct bpf_map *map)
 		return NULL;
 }
 
-static void codegen_btf_dump_printf(void *ct, const char *fmt, va_list args)
+static void codegen_btf_dump_printf(void *ctx, const char *fmt, va_list args)
 {
 	vprintf(fmt, args);
 }
@@ -126,13 +126,6 @@ static int codegen_datasec_def(struct bpf_object *obj,
 		);
 		int need_off = sec_var->offset, align_off, align;
 		__u32 var_type_id = var->type;
-		const struct btf_type *t;
-
-		t = btf__type_by_id(btf, var_type_id);
-		while (btf_is_mod(t)) {
-			var_type_id = t->type;
-			t = btf__type_by_id(btf, var_type_id);
-		}
 
 		if (off > need_off) {
 			p_err("Something is wrong for %s's variable #%d: need offset %d, already at %d.\n",
@@ -176,12 +169,14 @@ static int codegen_datasec_def(struct bpf_object *obj,
 
 static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
 {
+	/* strip out const/volatile/restrict modifiers for datasecs */
+	DECLARE_LIBBPF_OPTS(btf_dump_opts, opts, .strip_mods = true);
 	struct btf *btf = bpf_object__btf(obj);
 	int n = btf__get_nr_types(btf);
 	struct btf_dump *d;
 	int i, err = 0;
 
-	d = btf_dump__new(btf, NULL, NULL, codegen_btf_dump_printf);
+	d = btf_dump__new(btf, NULL, &opts, codegen_btf_dump_printf);
 	if (IS_ERR(d))
 		return PTR_ERR(d);
 
diff --git a/tools/testing/selftests/bpf/prog_tests/skeleton.c b/tools/testing/selftests/bpf/prog_tests/skeleton.c
index fa153cf67b1b..fe87b77af459 100644
--- a/tools/testing/selftests/bpf/prog_tests/skeleton.c
+++ b/tools/testing/selftests/bpf/prog_tests/skeleton.c
@@ -41,7 +41,7 @@ void test_skeleton(void)
 	CHECK(bss->in4 != 0, "in4", "got %lld != exp %lld\n", bss->in4, 0LL);
 	CHECK(bss->out4 != 0, "out4", "got %lld != exp %lld\n", bss->out4, 0LL);
 
-	CHECK(rodata->in6 != 0, "in6", "got %d != exp %d\n", rodata->in6, 0);
+	CHECK(rodata->in.in6 != 0, "in6", "got %d != exp %d\n", rodata->in.in6, 0);
 	CHECK(bss->out6 != 0, "out6", "got %d != exp %d\n", bss->out6, 0);
 
 	/* validate we can pre-setup global variables, even in .bss */
@@ -49,7 +49,7 @@ void test_skeleton(void)
 	data->in2 = 11;
 	bss->in3 = 12;
 	bss->in4 = 13;
-	rodata->in6 = 14;
+	rodata->in.in6 = 14;
 
 	err = test_skeleton__load(skel);
 	if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
@@ -60,7 +60,7 @@ void test_skeleton(void)
 	CHECK(data->in2 != 11, "in2", "got %lld != exp %lld\n", data->in2, 11LL);
 	CHECK(bss->in3 != 12, "in3", "got %d != exp %d\n", bss->in3, 12);
 	CHECK(bss->in4 != 13, "in4", "got %lld != exp %lld\n", bss->in4, 13LL);
-	CHECK(rodata->in6 != 14, "in6", "got %d != exp %d\n", rodata->in6, 14);
+	CHECK(rodata->in.in6 != 14, "in6", "got %d != exp %d\n", rodata->in.in6, 14);
 
 	/* now set new values and attach to get them into outX variables */
 	data->in1 = 1;
diff --git a/tools/testing/selftests/bpf/progs/test_skeleton.c b/tools/testing/selftests/bpf/progs/test_skeleton.c
index 77ae86f44db5..374ccef704e1 100644
--- a/tools/testing/selftests/bpf/progs/test_skeleton.c
+++ b/tools/testing/selftests/bpf/progs/test_skeleton.c
@@ -20,7 +20,9 @@ long long in4 __attribute__((aligned(64))) = 0;
 struct s in5 = {};
 
 /* .rodata section */
-const volatile int in6 = 0;
+const volatile struct {
+	const int in6;
+} in = {};
 
 /* .data section */
 int out1 = -1;
@@ -46,7 +48,7 @@ int handler(const void *ctx)
 	out3 = in3;
 	out4 = in4;
 	out5 = in5;
-	out6 = in6;
+	out6 = in.in6;
 
 	bpf_syscall = CONFIG_BPF_SYSCALL;
 	kern_ver = LINUX_KERNEL_VERSION;
-- 
2.24.1