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Date:	Fri, 21 Dec 2012 01:01:32 +0100
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	linux-kernel@...r.kernel.org,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	jonathon@...masters.org, Michael Kerrisk <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

Hi Rusty,

On Mon, Oct 22, 2012 at 9:39 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>>> FIX: add flags arg to sys_finit_module()
>>>
>>> Thanks to Michael Kerrisk for keeping us honest.
>>
>> w00t! Thanks, Rusty ;-).
>>
>> Acked-by: Michael Kerrisk <mtk.manpages@...il.com>
>
> Here's the version I ended up with when I added two flags.
>
> Lucas, is this useful to you?
>
> BTW Michael: why aren't the syscall man pages in the kernel source?
>
> Thanks,
> Rusty.
>
> module: add flags arg to sys_finit_module()
>
> Thanks to Michael Kerrisk for keeping us honest.  These flags are actually
> useful for eliminating the only case where kmod has to mangle a module's
> internals: for overriding module versioning.

The description here is rather thin. Could you supply a sentence or
two for each of MODULE_INIT_IGNORE_MODVERSIONS and
MODULE_INIT_IGNORE_VERMAGIC that would be suitable for the manual
page?

Thanks,

Michael


>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 32bc035..8cf7b50 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -868,5 +868,5 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
>
>  asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
>                          unsigned long idx1, unsigned long idx2);
> -asmlinkage long sys_finit_module(int fd, const char __user *uargs);
> +asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags);
>  #endif
> diff --git a/include/uapi/linux/module.h b/include/uapi/linux/module.h
> new file mode 100644
> index 0000000..38da425
> --- /dev/null
> +++ b/include/uapi/linux/module.h
> @@ -0,0 +1,8 @@
> +#ifndef _UAPI_LINUX_MODULE_H
> +#define _UAPI_LINUX_MODULE_H
> +
> +/* Flags for sys_finit_module: */
> +#define MODULE_INIT_IGNORE_MODVERSIONS 1
> +#define MODULE_INIT_IGNORE_VERMAGIC    2
> +
> +#endif /* _UAPI_LINUX_MODULE_H */
> diff --git a/kernel/module.c b/kernel/module.c
> index 261bf82..55b49cd 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -61,6 +61,7 @@
>  #include <linux/pfn.h>
>  #include <linux/bsearch.h>
>  #include <linux/fips.h>
> +#include <uapi/linux/module.h>
>  #include "module-internal.h"
>
>  #define CREATE_TRACE_POINTS
> @@ -2569,7 +2570,7 @@ static void free_copy(struct load_info *info)
>         vfree(info->hdr);
>  }
>
> -static int rewrite_section_headers(struct load_info *info)
> +static int rewrite_section_headers(struct load_info *info, int flags)
>  {
>         unsigned int i;
>
> @@ -2597,7 +2598,10 @@ static int rewrite_section_headers(struct load_info *info)
>         }
>
>         /* Track but don't keep modinfo and version sections. */
> -       info->index.vers = find_sec(info, "__versions");
> +       if (flags & MODULE_INIT_IGNORE_MODVERSIONS)
> +               info->index.vers = 0; /* Pretend no __versions section! */
> +       else
> +               info->index.vers = find_sec(info, "__versions");
>         info->index.info = find_sec(info, ".modinfo");
>         info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
>         info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
> @@ -2612,7 +2617,7 @@ static int rewrite_section_headers(struct load_info *info)
>   * Return the temporary module pointer (we'll replace it with the final
>   * one when we move the module sections around).
>   */
> -static struct module *setup_load_info(struct load_info *info)
> +static struct module *setup_load_info(struct load_info *info, int flags)
>  {
>         unsigned int i;
>         int err;
> @@ -2623,7 +2628,7 @@ static struct module *setup_load_info(struct load_info *info)
>         info->secstrings = (void *)info->hdr
>                 + info->sechdrs[info->hdr->e_shstrndx].sh_offset;
>
> -       err = rewrite_section_headers(info);
> +       err = rewrite_section_headers(info, flags);
>         if (err)
>                 return ERR_PTR(err);
>
> @@ -2661,11 +2666,14 @@ static struct module *setup_load_info(struct load_info *info)
>         return mod;
>  }
>
> -static int check_modinfo(struct module *mod, struct load_info *info)
> +static int check_modinfo(struct module *mod, struct load_info *info, int flags)
>  {
>         const char *modmagic = get_modinfo(info, "vermagic");
>         int err;
>
> +       if (flags & MODULE_INIT_IGNORE_VERMAGIC)
> +               modmagic = NULL;
> +
>         /* This is allowed: modprobe --force will invalidate it. */
>         if (!modmagic) {
>                 err = try_to_force_load(mod, "bad vermagic");
> @@ -2901,18 +2909,18 @@ int __weak module_frob_arch_sections(Elf_Ehdr *hdr,
>         return 0;
>  }
>
> -static struct module *layout_and_allocate(struct load_info *info)
> +static struct module *layout_and_allocate(struct load_info *info, int flags)
>  {
>         /* Module within temporary copy. */
>         struct module *mod;
>         Elf_Shdr *pcpusec;
>         int err;
>
> -       mod = setup_load_info(info);
> +       mod = setup_load_info(info, flags);
>         if (IS_ERR(mod))
>                 return mod;
>
> -       err = check_modinfo(mod, info);
> +       err = check_modinfo(mod, info, flags);
>         if (err)
>                 return ERR_PTR(err);
>
> @@ -3094,7 +3102,8 @@ static int may_init_module(void)
>
>  /* Allocate and load the module: note that size of section 0 is always
>     zero, and we rely on this for optional sections. */
> -static int load_module(struct load_info *info, const char __user *uargs)
> +static int load_module(struct load_info *info, const char __user *uargs,
> +                      int flags)
>  {
>         struct module *mod, *old;
>         long err;
> @@ -3108,7 +3117,7 @@ static int load_module(struct load_info *info, const char __user *uargs)
>                 goto free_copy;
>
>         /* Figure out module layout, and allocate all the memory. */
> -       mod = layout_and_allocate(info);
> +       mod = layout_and_allocate(info, flags);
>         if (IS_ERR(mod)) {
>                 err = PTR_ERR(mod);
>                 goto free_copy;
> @@ -3257,10 +3269,10 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
>         if (err)
>                 return err;
>
> -       return load_module(&info, uargs);
> +       return load_module(&info, uargs, 0);
>  }
>
> -SYSCALL_DEFINE2(finit_module, int, fd, const char __user *, uargs)
> +SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
>  {
>         int err;
>         struct load_info info = { };
> @@ -3269,13 +3281,17 @@ SYSCALL_DEFINE2(finit_module, int, fd, const char __user *, uargs)
>         if (err)
>                 return err;
>
> -       pr_debug("finit_module: fd=%d, uargs=%p\n", fd, uargs);
> +       pr_debug("finit_module: fd=%d, uargs=%p, flags=%i\n", fd, uargs, flags);
> +
> +       if (flags & ~(MODULE_INIT_IGNORE_MODVERSIONS
> +                     |MODULE_INIT_IGNORE_VERMAGIC))
> +               return -EINVAL;
>
>         err = copy_module_from_fd(fd, &info);
>         if (err)
>                 return err;
>
> -       return load_module(&info, uargs);
> +       return load_module(&info, uargs, flags);
>  }
>
>  static inline int within(unsigned long addr, void *start, unsigned long size)
> --
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-- 
Michael Kerrisk Linux man-pages maintainer;
http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface", http://blog.man7.org/
--
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