From b1ae6dc41eaaa98bb75671e0f3665bfda248c3e7 Mon Sep 17 00:00:00 2001 From: Dmitry Torokhov Date: Wed, 5 Jan 2022 13:55:12 -0800 Subject: module: add in-kernel support for decompressing Current scheme of having userspace decompress kernel modules before loading them into the kernel runs afoul of LoadPin security policy, as it loses link between the source of kernel module on the disk and binary blob that is being loaded into the kernel. To solve this issue let's implement decompression in kernel, so that we can pass a file descriptor of compressed module file into finit_module() which will keep LoadPin happy. To let userspace know what compression/decompression scheme kernel supports it will create /sys/module/compression attribute. kmod can read this attribute and decide if it can pass compressed file to finit_module(). New MODULE_INIT_COMPRESSED_DATA flag indicates that the kernel should attempt to decompress the data read from file descriptor prior to trying load the module. To simplify things kernel will only implement single decompression method matching compression method selected when generating modules. This patch implements gzip and xz; more can be added later, Signed-off-by: Dmitry Torokhov Signed-off-by: Luis Chamberlain --- include/uapi/linux/module.h | 1 + init/Kconfig | 13 +++ kernel/Makefile | 1 + kernel/module-internal.h | 19 ++++ kernel/module.c | 35 ++++-- kernel/module_decompress.c | 271 ++++++++++++++++++++++++++++++++++++++++++++ 6 files changed, 329 insertions(+), 11 deletions(-) create mode 100644 kernel/module_decompress.c diff --git a/include/uapi/linux/module.h b/include/uapi/linux/module.h index 50d98ec5e866..03a33ffffcba 100644 --- a/include/uapi/linux/module.h +++ b/include/uapi/linux/module.h @@ -5,5 +5,6 @@ /* Flags for sys_finit_module: */ #define MODULE_INIT_IGNORE_MODVERSIONS 1 #define MODULE_INIT_IGNORE_VERMAGIC 2 +#define MODULE_INIT_COMPRESSED_FILE 4 #endif /* _UAPI_LINUX_MODULE_H */ diff --git a/init/Kconfig b/init/Kconfig index f2ae41e6717f..faf3a4b5cc8f 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2274,6 +2274,19 @@ config MODULE_COMPRESS_ZSTD endchoice +config MODULE_DECOMPRESS + bool "Support in-kernel module decompression" + depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ + select ZLIB_INFLATE if MODULE_COMPRESS_GZIP + select XZ_DEC if MODULE_COMPRESS_XZ + help + + Support for decompressing kernel modules by the kernel itself + instead of relying on userspace to perform this task. Useful when + load pinning security policy is enabled. + + If unsure, say N. + config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS bool "Allow loading of modules with missing namespace imports" help diff --git a/kernel/Makefile b/kernel/Makefile index 186c49582f45..56f4ee97f328 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -67,6 +67,7 @@ obj-y += up.o endif obj-$(CONFIG_UID16) += uid16.o obj-$(CONFIG_MODULES) += module.o +obj-$(CONFIG_MODULE_DECOMPRESS) += module_decompress.o obj-$(CONFIG_MODULE_SIG) += module_signing.o obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signature.o obj-$(CONFIG_KALLSYMS) += kallsyms.o diff --git a/kernel/module-internal.h b/kernel/module-internal.h index 33783abc377b..8c381c99062f 100644 --- a/kernel/module-internal.h +++ b/kernel/module-internal.h @@ -22,6 +22,11 @@ struct load_info { bool sig_ok; #ifdef CONFIG_KALLSYMS unsigned long mod_kallsyms_init_off; +#endif +#ifdef CONFIG_MODULE_DECOMPRESS + struct page **pages; + unsigned int max_pages; + unsigned int used_pages; #endif struct { unsigned int sym, str, mod, vers, info, pcpu; @@ -29,3 +34,17 @@ struct load_info { }; extern int mod_verify_sig(const void *mod, struct load_info *info); + +#ifdef CONFIG_MODULE_DECOMPRESS +int module_decompress(struct load_info *info, const void *buf, size_t size); +void module_decompress_cleanup(struct load_info *info); +#else +static inline int module_decompress(struct load_info *info, + const void *buf, size_t size) +{ + return -EOPNOTSUPP; +} +static inline void module_decompress_cleanup(struct load_info *info) +{ +} +#endif diff --git a/kernel/module.c b/kernel/module.c index 320ec908045f..34fe2824eb56 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -3173,9 +3173,12 @@ out: return err; } -static void free_copy(struct load_info *info) +static void free_copy(struct load_info *info, int flags) { - vfree(info->hdr); + if (flags & MODULE_INIT_COMPRESSED_FILE) + module_decompress_cleanup(info); + else + vfree(info->hdr); } static int rewrite_section_headers(struct load_info *info, int flags) @@ -4124,7 +4127,7 @@ static int load_module(struct load_info *info, const char __user *uargs, } /* Get rid of temporary copy. */ - free_copy(info); + free_copy(info, flags); /* Done! */ trace_module_load(mod); @@ -4173,7 +4176,7 @@ static int load_module(struct load_info *info, const char __user *uargs, module_deallocate(mod, info); free_copy: - free_copy(info); + free_copy(info, flags); return err; } @@ -4200,7 +4203,8 @@ SYSCALL_DEFINE3(init_module, void __user *, umod, SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) { struct load_info info = { }; - void *hdr = NULL; + void *buf = NULL; + int len; int err; err = may_init_module(); @@ -4210,15 +4214,24 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) pr_debug("finit_module: fd=%d, uargs=%p, flags=%i\n", fd, uargs, flags); if (flags & ~(MODULE_INIT_IGNORE_MODVERSIONS - |MODULE_INIT_IGNORE_VERMAGIC)) + |MODULE_INIT_IGNORE_VERMAGIC + |MODULE_INIT_COMPRESSED_FILE)) return -EINVAL; - err = kernel_read_file_from_fd(fd, 0, &hdr, INT_MAX, NULL, + len = kernel_read_file_from_fd(fd, 0, &buf, INT_MAX, NULL, READING_MODULE); - if (err < 0) - return err; - info.hdr = hdr; - info.len = err; + if (len < 0) + return len; + + if (flags & MODULE_INIT_COMPRESSED_FILE) { + err = module_decompress(&info, buf, len); + vfree(buf); /* compressed data is no longer needed */ + if (err) + return err; + } else { + info.hdr = buf; + info.len = len; + } return load_module(&info, uargs, flags); } diff --git a/kernel/module_decompress.c b/kernel/module_decompress.c new file mode 100644 index 000000000000..aeefd95a3337 --- /dev/null +++ b/kernel/module_decompress.c @@ -0,0 +1,271 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright 2021 Google LLC. + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +#include "module-internal.h" + +static int module_extend_max_pages(struct load_info *info, unsigned int extent) +{ + struct page **new_pages; + + new_pages = kvmalloc_array(info->max_pages + extent, + sizeof(info->pages), GFP_KERNEL); + if (!new_pages) + return -ENOMEM; + + memcpy(new_pages, info->pages, info->max_pages * sizeof(info->pages)); + kvfree(info->pages); + info->pages = new_pages; + info->max_pages += extent; + + return 0; +} + +static struct page *module_get_next_page(struct load_info *info) +{ + struct page *page; + int error; + + if (info->max_pages == info->used_pages) { + error = module_extend_max_pages(info, info->used_pages); + if (error) + return ERR_PTR(error); + } + + page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM); + if (!page) + return ERR_PTR(-ENOMEM); + + info->pages[info->used_pages++] = page; + return page; +} + +#ifdef CONFIG_MODULE_COMPRESS_GZIP +#include +#define MODULE_COMPRESSION gzip +#define MODULE_DECOMPRESS_FN module_gzip_decompress + +/* + * Calculate length of the header which consists of signature, header + * flags, time stamp and operating system ID (10 bytes total), plus + * an optional filename. + */ +static size_t module_gzip_header_len(const u8 *buf, size_t size) +{ + const u8 signature[] = { 0x1f, 0x8b, 0x08 }; + size_t len = 10; + + if (size < len || memcmp(buf, signature, sizeof(signature))) + return 0; + + if (buf[3] & 0x08) { + do { + /* + * If we can't find the end of the file name we must + * be dealing with a corrupted file. + */ + if (len == size) + return 0; + } while (buf[len++] != '\0'); + } + + return len; +} + +static ssize_t module_gzip_decompress(struct load_info *info, + const void *buf, size_t size) +{ + struct z_stream_s s = { 0 }; + size_t new_size = 0; + size_t gzip_hdr_len; + ssize_t retval; + int rc; + + gzip_hdr_len = module_gzip_header_len(buf, size); + if (!gzip_hdr_len) { + pr_err("not a gzip compressed module\n"); + return -EINVAL; + } + + s.next_in = buf + gzip_hdr_len; + s.avail_in = size - gzip_hdr_len; + + s.workspace = kmalloc(zlib_inflate_workspacesize(), GFP_KERNEL); + if (!s.workspace) + return -ENOMEM; + + rc = zlib_inflateInit2(&s, -MAX_WBITS); + if (rc != Z_OK) { + pr_err("failed to initialize decompresser: %d\n", rc); + retval = -EINVAL; + goto out; + } + + do { + struct page *page = module_get_next_page(info); + if (!page) { + retval = -ENOMEM; + goto out_inflate_end; + } + + s.next_out = kmap(page); + s.avail_out = PAGE_SIZE; + rc = zlib_inflate(&s, 0); + kunmap(page); + + new_size += PAGE_SIZE - s.avail_out; + } while (rc == Z_OK); + + if (rc != Z_STREAM_END) { + pr_err("decompression failed with status %d\n", rc); + retval = -EINVAL; + goto out_inflate_end; + } + + retval = new_size; + +out_inflate_end: + zlib_inflateEnd(&s); +out: + kfree(s.workspace); + return retval; +} +#elif CONFIG_MODULE_COMPRESS_XZ +#include +#define MODULE_COMPRESSION xz +#define MODULE_DECOMPRESS_FN module_xz_decompress + +static ssize_t module_xz_decompress(struct load_info *info, + const void *buf, size_t size) +{ + static const u8 signature[] = { 0xfd, '7', 'z', 'X', 'Z', 0 }; + struct xz_dec *xz_dec; + struct xz_buf xz_buf; + enum xz_ret xz_ret; + size_t new_size = 0; + ssize_t retval; + + if (size < sizeof(signature) || + memcmp(buf, signature, sizeof(signature))) { + pr_err("not an xz compressed module\n"); + return -EINVAL; + } + + xz_dec = xz_dec_init(XZ_DYNALLOC, (u32)-1); + if (!xz_dec) + return -ENOMEM; + + xz_buf.in_size = size; + xz_buf.in = buf; + xz_buf.in_pos = 0; + + do { + struct page *page = module_get_next_page(info); + if (!page) { + retval = -ENOMEM; + goto out; + } + + xz_buf.out = kmap(page); + xz_buf.out_pos = 0; + xz_buf.out_size = PAGE_SIZE; + xz_ret = xz_dec_run(xz_dec, &xz_buf); + kunmap(page); + + new_size += xz_buf.out_pos; + } while (xz_buf.out_pos == PAGE_SIZE && xz_ret == XZ_OK); + + if (xz_ret != XZ_STREAM_END) { + pr_err("decompression failed with status %d\n", xz_ret); + retval = -EINVAL; + goto out; + } + + retval = new_size; + + out: + xz_dec_end(xz_dec); + return retval; +} +#else +#error "Unexpected configuration for CONFIG_MODULE_DECOMPRESS" +#endif + +int module_decompress(struct load_info *info, const void *buf, size_t size) +{ + unsigned int n_pages; + ssize_t data_size; + int error; + + /* + * Start with number of pages twice as big as needed for + * compressed data. + */ + n_pages = DIV_ROUND_UP(size, PAGE_SIZE) * 2; + error = module_extend_max_pages(info, n_pages); + + data_size = MODULE_DECOMPRESS_FN(info, buf, size); + if (data_size < 0) { + error = data_size; + goto err; + } + + info->hdr = vmap(info->pages, info->used_pages, VM_MAP, PAGE_KERNEL); + if (!info->hdr) { + error = -ENOMEM; + goto err; + } + + info->len = data_size; + return 0; + +err: + module_decompress_cleanup(info); + return error; +} + +void module_decompress_cleanup(struct load_info *info) +{ + int i; + + if (info->hdr) + vunmap(info->hdr); + + for (i = 0; i < info->used_pages; i++) + __free_page(info->pages[i]); + + kvfree(info->pages); + + info->pages = NULL; + info->max_pages = info->used_pages = 0; +} + +static ssize_t compression_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%s\n", __stringify(MODULE_COMPRESSION)); +} +static struct kobj_attribute module_compression_attr = __ATTR_RO(compression); + +static int __init module_decompress_sysfs_init(void) +{ + int error; + + error = sysfs_create_file(&module_kset->kobj, + &module_compression_attr.attr); + if (error) + pr_warn("Failed to create 'compression' attribute"); + + return 0; +} +late_initcall(module_decompress_sysfs_init); -- cgit v1.2.3