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Date: Tue, 20 Oct 2009 09:12:54 +0900
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: "Ryan C. Gordon" <icculus@...ulus.org>
CC: linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/2] binfmt_elf: FatELF support for kernel modules.
On 10/19/09 23:41, Ryan C. Gordon wrote:
> Allows kernel modules to be FatELF binaries.
>
> Details, rationale, tools, and patches for handling FatELF binaries can be
> found at http://icculus.org/fatelf/
>
> Please note that this requires an updated depmod and modprobe to be truly
> effective, but an unmodified insmod can work with FatELF binaries.
>
This seems much more dubious. It would only encourage more binary
modules, which we're not very keen on doing.
J
> Signed-off-by: Ryan C. Gordon <icculus@...ulus.org>
> ---
> kernel/module.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 files changed, 67 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 8b7d880..cda8f79 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2066,13 +2066,69 @@ static inline void kmemleak_load_module(struct module *mod, Elf_Ehdr *hdr,
> }
> #endif
>
> +/*
> + * See if we're a valid FatELF binary, find the right record, and
> + * return the offset of that record within the binary. Returns NULL if there's
> + * a problem, or a pointer to the real ELF header if we're okay.
> + * If we don't see the FatELF magic number, we assume this is a regular ELF
> + * binary and let the regular ELF checks handle it.
> + *
> + * This is a simplified version of examine_fatelf in fs/binfmt_elf.c
> + */
> +static Elf_Ehdr *examine_fatelf_module(const unsigned char *hdr,
> + const unsigned long len)
> +{
> + Elf_Ehdr elf;
> + int records, i;
> + const fatelf_hdr *fatelf = (const fatelf_hdr *) hdr;
> +
> + if (likely(le32_to_cpu(fatelf->magic) != FATELF_MAGIC)) {
> + return (Elf_Ehdr *) hdr; /* not FatELF; not an error. */
> + } else if (unlikely(le16_to_cpu(fatelf->version) != 1)) {
> + return NULL; /* Unrecognized format version. */
> + }
> +
> + memset(&elf, 0, sizeof (elf));
> +
> + records = (int) fatelf->num_records; /* uint8, no byteswap needed */
> + for (i = 0; i < records; i++) {
> + const fatelf_record *record = &fatelf->records[i];
> +
> + /* Fill in the data elf_check_arch() might care about. */
> + elf.e_ident[EI_OSABI] = record->osabi;
> + elf.e_ident[EI_CLASS] = record->word_size;
> + elf.e_ident[EI_DATA] = record->byte_order;
> + elf.e_machine = le16_to_cpu(record->machine);
> +
> + if (likely(!elf_check_arch(&elf))) {
> + continue; /* Unsupported CPU architecture. */
> + } else {
> + const __u64 rec_offset = le64_to_cpu(record->offset);
> + const __u64 rec_size = le64_to_cpu(record->size);
> + const __u64 end_offset = rec_offset + rec_size;
> + const unsigned long uloff = (unsigned long) rec_offset;
> +
> + if (unlikely(end_offset < rec_offset)) {
> + continue; /* overflow (corrupt file?)... */
> + } else if (unlikely(end_offset > len)) {
> + continue; /* past EOF. */
> + }
> +
> + return (Elf_Ehdr *) (hdr + uloff);
> + }
> + }
> +
> + return NULL; /* no binaries we could use. */
> +}
> +
> /* Allocate and load the module: note that size of section 0 is always
> zero, and we rely on this for optional sections. */
> static noinline struct module *load_module(void __user *umod,
> unsigned long len,
> const char __user *uargs)
> {
> - Elf_Ehdr *hdr;
> + Elf_Ehdr *hdr_alloc; /* returned from vmalloc */
> + Elf_Ehdr *hdr; /* adjusted hdr_alloc for FatELF */
> Elf_Shdr *sechdrs;
> char *secstrings, *args, *modmagic, *strtab = NULL;
> char *staging;
> @@ -2094,14 +2150,20 @@ static noinline struct module *load_module(void __user *umod,
>
> /* Suck in entire file: we'll want most of it. */
> /* vmalloc barfs on "unusual" numbers. Check here */
> - if (len > 64 * 1024 * 1024 || (hdr = vmalloc(len)) == NULL)
> + if (len > 64 * 1024 * 1024 || (hdr_alloc = vmalloc(len)) == NULL)
> return ERR_PTR(-ENOMEM);
>
> - if (copy_from_user(hdr, umod, len) != 0) {
> + if (copy_from_user(hdr_alloc, umod, len) != 0) {
> err = -EFAULT;
> goto free_hdr;
> }
>
> + hdr = examine_fatelf_module((unsigned char *) hdr_alloc, len);
> + if (hdr == NULL) {
> + err = -ENOEXEC;
> + goto free_hdr;
> + }
> +
> /* Sanity checks against insmoding binaries or wrong arch,
> weird elf version */
> if (memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0
> @@ -2505,7 +2567,7 @@ static noinline struct module *load_module(void __user *umod,
> add_notes_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
>
> /* Get rid of temporary copy */
> - vfree(hdr);
> + vfree(hdr_alloc);
>
> trace_module_load(mod);
>
> @@ -2538,7 +2600,7 @@ static noinline struct module *load_module(void __user *umod,
> kfree(args);
> kfree(strmap);
> free_hdr:
> - vfree(hdr);
> + vfree(hdr_alloc);
> return ERR_PTR(err);
>
> truncated:
>
--
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