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Message-ID: <CAK7LNAQ-wMTOaCuBab-JOfz4ggefNiEBmiKCUpuFncTqS0P3xQ@mail.gmail.com>
Date: Thu, 7 Nov 2024 16:55:46 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mcgrof@...nel.org, x86@...nel.org, hpa@...or.com, petr.pavlu@...e.com,
samitolvanen@...gle.com, da.gomez@...sung.com, nathan@...nel.org,
nicolas@...sle.eu, linux-kernel@...r.kernel.org,
linux-modules@...r.kernel.org, linux-kbuild@...r.kernel.org,
hch@...radead.org, gregkh@...uxfoundation.org
Subject: Re: [RFC] module: Strict per-modname namespaces
On Thu, Nov 7, 2024 at 4:02 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Hi,
>
> I've been wanting $topic for a while, and having just stumbled into the
> whole namespace thing by accident, I figured I'd give it a go, most if
> the hard parts seem to have already been done.
>
> It reserves and disallows imports on any "MODULE_${name}" namespace,
> while it implicitly adds the same namespace to every module.
>
> This allows exports targeted at specific modules and no others -- one
> random example included. I've hated the various kvm exports we've had
> for a while, and strictly limiting them to the kvm module helps
> alleviate some abuse potential.
>
> ---
> arch/x86/kernel/fpu/core.c | 2 +-
> kernel/module/main.c | 28 ++++++++++++++++++++++++++--
> scripts/mod/modpost.c | 29 ++++++++++++++++++++---------
> 3 files changed, 47 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 1209c7aebb21..23b188a53d9d 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -366,7 +366,7 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
> fpregs_unlock();
> return 0;
> }
> -EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
> +EXPORT_SYMBOL_NS_GPL(fpu_swap_kvm_fpstate, MODULE_kvm);
>
> void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
> unsigned int size, u64 xfeatures, u32 pkru)
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 49b9bca9de12..b30af879c2cb 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1070,6 +1070,13 @@ static int verify_namespace_is_imported(const struct load_info *info,
>
> namespace = kernel_symbol_namespace(sym);
> if (namespace && namespace[0]) {
> + /*
> + * Implicitly import MODULE_${mod->name} namespace.
> + */
> + if (strncmp(namespace, "MODULE_", 7) == 0 &&
> + strcmp(namespace+7, mod->name) == 0)
> + return 0;
> +
> for_each_modinfo_entry(imported_namespace, info, "import_ns") {
> if (strcmp(namespace, imported_namespace) == 0)
> return 0;
> @@ -1613,15 +1620,30 @@ static void module_license_taint_check(struct module *mod, const char *license)
> }
> }
>
> -static void setup_modinfo(struct module *mod, struct load_info *info)
> +static int setup_modinfo(struct module *mod, struct load_info *info)
> {
> struct module_attribute *attr;
> + char *imported_namespace;
> int i;
>
> for (i = 0; (attr = modinfo_attrs[i]); i++) {
> if (attr->setup)
> attr->setup(mod, get_modinfo(info, attr->attr.name));
> }
> +
> + for_each_modinfo_entry(imported_namespace, info, "import_ns") {
> + /*
> + * 'MODULE_' prefixed namespaces are implicit, disallow
> + * explicit imports.
> + */
> + if (strstarts(imported_namespace, "MODULE_")) {
> + pr_err("%s: module tries to import module namespace: %s\n",
> + mod->name, imported_namespace);
> + return -EPERM;
> + }
> + }
> +
> + return 0;
> }
>
> static void free_modinfo(struct module *mod)
> @@ -2935,7 +2957,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
> goto free_unload;
>
> /* Set up MODINFO_ATTR fields */
> - setup_modinfo(mod, info);
> + err = setup_modinfo(mod, info);
> + if (err)
> + goto free_modinfo;
>
> /* Fix up syms, so that st_value is a pointer to location. */
> err = simplify_symbols(mod, info);
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 107393a8c48a..d1de3044ee03 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1553,8 +1553,19 @@ static void mod_set_crcs(struct module *mod)
> free(buf);
> }
>
> +static const char *mod_basename(const char *modname)
> +{
> + const char *basename = strrchr(modname, '/');
> + if (basename)
> + basename++;
> + else
> + basename = modname;
> + return basename;
> +}
> +
> static void read_symbols(const char *modname)
> {
> + char module_namespace[MODULE_NAME_LEN + 8];
> const char *symname;
> char *version;
> char *license;
> @@ -1586,12 +1597,16 @@ static void read_symbols(const char *modname)
> license = get_next_modinfo(&info, "license", license);
> }
>
> - namespace = get_modinfo(&info, "import_ns");
> - while (namespace) {
> + for (namespace = get_modinfo(&info, "import_ns"); namespace;
> + namespace = get_next_modinfo(&info, "import_ns", namespace)) {
The conversion from while() to for() is an unrelated change.
Split it to a separate patch if you want to change it.
> + if (strstarts(namespace, "MODULE_"))
> + error("importing implicit module namespace: %s\n", namespace);
> +
> add_namespace(&mod->imported_namespaces, namespace);
> - namespace = get_next_modinfo(&info, "import_ns",
> - namespace);
> }
> + snprintf(module_namespace, sizeof(module_namespace), "MODULE_%s",
> + mod_basename(mod->name));
> + add_namespace(&mod->imported_namespaces, module_namespace);
>
> if (extra_warn && !get_modinfo(&info, "description"))
> warn("missing MODULE_DESCRIPTION() in %s\n", modname);
> @@ -1700,11 +1715,7 @@ static void check_exports(struct module *mod)
> s->crc_valid = exp->crc_valid;
> s->crc = exp->crc;
>
> - basename = strrchr(mod->name, '/');
> - if (basename)
> - basename++;
> - else
> - basename = mod->name;
> + basename = mod_basename(mod->name);
This is an unrelated change.
So, it should be split into a separate prerequisite patch,
something like, "modpost: introduce mod_basename() helper"
> if (!contains_namespace(&mod->imported_namespaces, exp->namespace)) {
> modpost_log(!allow_missing_ns_imports,
--
Best Regards
Masahiro Yamada
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