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: 985ead416df3 ("bpftool: Add skeleton codegen command")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200713232409.3062144-3-andriin@fb.com

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 10de76b296ba148cd918b64b86dcd97c1e3217f9..b59d26e89367248064473cfbe10172519331f14d 100644 (file)
--- 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);
 }
@@ -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",

diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 227d3f8448014a2e6119513ef8744b02b8ac4f14..491c7b41ffdce77545f635baf60c070ea1ca37b7 100644 (file)
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -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,

diff --git a/tools/testing/selftests/bpf/prog_tests/skeleton.c b/tools/testing/selftests/bpf/prog_tests/skeleton.c
index fa153cf67b1bb984bcd29f08ebe40f65cc351e9f..fe87b77af459727b3e37f73f7ea11c09b8075db6 100644 (file)
--- 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 77ae86f44db5d7458ca6650939e59e9a3edfa2dc..374ccef704e10e56e95cb8ced5f9e84bc3adfb2d 100644 (file)
--- 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;