Commit 0b20933d authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

tools/bpftool: Strip away modifiers from global variables 



Reliably remove all the type modifiers from read-only (.rodata) 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.

Fixes: 985ead41 ("bpftool: Add skeleton codegen command")
Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200713232409.3062144-3-andriin@fb.com
parent 7c819e70

tools/bpf/bpftool/gen.c

+10 −13
Original line number Diff line number Diff line
@@ -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);

}
@@ -104,17 +104,20 @@ static int codegen_datasec_def(struct bpf_object *obj, 
	int i, err, off = 0, pad_cnt = 0, vlen = btf_vlen(sec);

	const char *sec_ident;

	char var_ident[256];

	bool strip_mods = false;



	if (strcmp(sec_name, ".data") == 0)

	if (strcmp(sec_name, ".data") == 0) {

		sec_ident = "data";

	else if (strcmp(sec_name, ".bss") == 0)

	} else if (strcmp(sec_name, ".bss") == 0) {

		sec_ident = "bss";

	else if (strcmp(sec_name, ".rodata") == 0)

	} else if (strcmp(sec_name, ".rodata") == 0) {

		sec_ident = "rodata";

	else if (strcmp(sec_name, ".kconfig") == 0)

		strip_mods = true;

	} else if (strcmp(sec_name, ".kconfig") == 0) {

		sec_ident = "kconfig";

	else

	} else {

		return 0;

	}



	printf("	struct %s__%s {\n", obj_name, sec_ident);

	for (i = 0; i < vlen; i++, sec_var++) {
@@ -123,16 +126,10 @@ static int codegen_datasec_def(struct bpf_object *obj, 
		DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts,

			.field_name = var_ident,

			.indent_level = 2,

			.strip_mods = strip_mods,

		);

		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",

tools/lib/bpf/btf.h

+1 −1
Original line number Diff line number Diff line
@@ -147,7 +147,7 @@ struct btf_dump_emit_type_decl_opts { 
	/* strip all the const/volatile/restrict mods */

	bool strip_mods;

};

#define btf_dump_emit_type_decl_opts__last_field indent_level

#define btf_dump_emit_type_decl_opts__last_field strip_mods



LIBBPF_API int

btf_dump__emit_type_decl(struct btf_dump *d, __u32 id,

tools/testing/selftests/bpf/prog_tests/skeleton.c

+3 −3
Original line number Diff line number Diff line
@@ -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;

tools/testing/selftests/bpf/progs/test_skeleton.c

+4 −2
Original line number Diff line number Diff line
@@ -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;

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