When kernel module loading failed, user space only get one of the
following error messages:
- -ENOEXEC
This is the most confusing one. From corrupted ELF header to bad
WRITE|EXEC flags check introduced by in module_enforce_rwx_sections()
all returns this error number.
- -EPERM
This is for blacklisted modules. But mod doesn't do extra explain
on this error either.
- -ENOMEM
The only error which needs no explain.
This means, if a user got "Exec format error" from modprobe, it provides
no meaningful way for the user to debug, and will take extra time
communicating to get extra info.
So this patch will add extra error messages for -ENOEXEC and -EPERM
errors, allowing user to do better debugging and reporting.
Signed-off-by: Qu Wenruo <[email protected]>
---
kernel/module.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
index 8fa2600bde6a..204bf29437b8 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2068,8 +2068,12 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
int i;
for (i = 0; i < hdr->e_shnum; i++) {
- if ((sechdrs[i].sh_flags & shf_wx) == shf_wx)
+ if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
+ pr_err(
+ "Module %s section %d has invalid WRITE|EXEC flags\n",
+ mod->name, i);
return -ENOEXEC;
+ }
}
return 0;
@@ -3797,8 +3801,10 @@ static int load_module(struct load_info *info, const char __user *uargs,
char *after_dashes;
err = elf_header_check(info);
- if (err)
+ if (err) {
+ pr_err("Module has invalid ELF header\n");
goto free_copy;
+ }
err = setup_load_info(info, flags);
if (err)
@@ -3806,6 +3812,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
if (blacklisted(info->name)) {
err = -EPERM;
+ pr_err("Module %s is blacklisted\n", info->name);
goto free_copy;
}
--
2.28.0
+++ Qu Wenruo [31/08/20 16:37 +0800]:
>When kernel module loading failed, user space only get one of the
>following error messages:
>- -ENOEXEC
> This is the most confusing one. From corrupted ELF header to bad
> WRITE|EXEC flags check introduced by in module_enforce_rwx_sections()
> all returns this error number.
>
>- -EPERM
> This is for blacklisted modules. But mod doesn't do extra explain
> on this error either.
>
>- -ENOMEM
> The only error which needs no explain.
>
>This means, if a user got "Exec format error" from modprobe, it provides
>no meaningful way for the user to debug, and will take extra time
>communicating to get extra info.
>
>So this patch will add extra error messages for -ENOEXEC and -EPERM
>errors, allowing user to do better debugging and reporting.
>
>Signed-off-by: Qu Wenruo <[email protected]>
Thanks for your patch, agreed that there should be more descriptive
error messages to help debug module loading issues.
>---
> kernel/module.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/module.c b/kernel/module.c
>index 8fa2600bde6a..204bf29437b8 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -2068,8 +2068,12 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> int i;
>
> for (i = 0; i < hdr->e_shnum; i++) {
>- if ((sechdrs[i].sh_flags & shf_wx) == shf_wx)
>+ if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
>+ pr_err(
>+ "Module %s section %d has invalid WRITE|EXEC flags\n",
>+ mod->name, i);
I think it's OK to put pr_err and the format string on the same line.
IMO the line break doesn't add much readability value in this case.
Also, we have access to secstrings in this function. We can print out
the section name with secstrings + sechdrs[i].sh_name in addition to
the section number, I think that would be helpful.
And can we reformat the message to start with the module name, similar
to other pr_err() sites? i.e.,
pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags",
mod->name, secstrings + sechdrs[i].sh_name, i)
The rest looks fine to me. Thanks!
Jessica