On Thu, Mar 06, 2025 at 11:36:55AM +0100, Petr Pavlu wrote:
> In the unlikely case that setting ro_after_init data to read-only fails, it
> is too late to cancel loading of the module. The loader then issues only
> a warning about the situation. Given that this reduces the kernel's
> protection, it was suggested to make the failure more visible by tainting
> the kernel.
>
> Allow TAINT_BAD_PAGE to be set per-module and use it in this case. The flag
> is set in similar situations and has the following description in
> Documentation/admin-guide/tainted-kernels.rst: "bad page referenced or some
> unexpected page flags".
>
> Adjust the warning that reports the failure to avoid references to internal
> functions and to add information about the kernel being tainted, both to
> match the style of other messages in the file. Additionally, merge the
> message on a single line because checkpatch.pl recommends that for the
> ability to grep for the string.
>
> Suggested-by: Kees Cook <k...@kernel.org>
> Signed-off-by: Petr Pavlu <petr.pa...@suse.com>
> ---
> I opted to use TAINT_BAD_PAGE for now because it seemed unnecessary to me
> to introduce a new flag only for this specific case. However, if we end up
> similarly checking set_memory_*() in the boot context, a separate flag
> would be probably better.
> ---
> kernel/module/main.c | 7 ++++---
> kernel/panic.c | 2 +-
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 1fb9ad289a6f..8f424a107b92 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -3030,10 +3030,11 @@ static noinline int do_init_module(struct module *mod)
> rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
> #endif
> ret = module_enable_rodata_ro_after_init(mod);
> - if (ret)
> - pr_warn("%s: module_enable_rodata_ro_after_init() returned %d, "
> - "ro_after_init data might still be writable\n",
> + if (ret) {
> + pr_warn("%s: write-protecting ro_after_init data failed with
> %d, the data might still be writable - tainting kernel\n",
This is quite large. Can we simplify it?
For 1 line grep parsing we can start writing at the beginning of the line as
it's done in some cases in fs/xfs/xfs_super.c. Proposals:
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 6d1094c6dea8..fc5510b8aa14 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2982,7 +2982,8 @@ static noinline int do_init_module(struct module *mod)
#endif
ret = module_enable_rodata_ro_after_init(mod);
if (ret) {
- pr_warn("%s: write-protecting ro_after_init data failed with
%d, the data might still be writable - tainting kernel\n",
+ pr_warn(
+"%s: write-protecting ro_after_init failed with %d - tainting kernel\n",
mod->name, ret);
add_taint_module(mod, TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
}
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 6d1094c6dea8..4fa0c80b2bb4 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2982,7 +2982,8 @@ static noinline int do_init_module(struct module *mod)
#endif
ret = module_enable_rodata_ro_after_init(mod);
if (ret) {
- pr_warn("%s: write-protecting ro_after_init data failed with
%d, the data might still be writable - tainting kernel\n",
+ pr_warn(
+"%s: ro_after_init failed with %d, data might be writable - tainting kernel\n",
mod->name, ret);
add_taint_module(mod, TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
}
Daniel
