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Message-ID: <87cz6mxyb7.ffs@tglx>
Date: Mon, 06 Feb 2023 22:45:48 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Song Liu <song@...nel.org>, linux-modules@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: hch@....de, kernel-team@...a.com, Song Liu <song@...nel.org>,
Luis Chamberlain <mcgrof@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Guenter Roeck <linux@...ck-us.net>,
Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v9] module: replace module_layout with module_memory
Song!
On Fri, Feb 03 2023 at 13:45, Song Liu wrote:
> diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
> index af7c322ebed6..9d4ecb6b1412 100644
> --- a/arch/arm/kernel/module-plts.c
> +++ b/arch/arm/kernel/module-plts.c
> @@ -30,7 +30,7 @@ static const u32 fixed_plts[] = {
>
> static bool in_init(const struct module *mod, unsigned long loc)
> {
> - return loc - (u32)mod->init_layout.base < mod->init_layout.size;
> + return within_module_init(loc, mod);
> }
>
> static void prealloc_fixed(struct mod_plt_sec *pltsec, struct plt_entries *plt)
> diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
> index 5a0a8f552a61..4bf94de272cb 100644
> --- a/arch/arm64/kernel/module-plts.c
> +++ b/arch/arm64/kernel/module-plts.c
> @@ -67,7 +67,7 @@ static bool plt_entries_equal(const struct plt_entry *a,
>
> static bool in_init(const struct module *mod, void *loc)
> {
> - return (u64)loc - (u64)mod->init_layout.base < mod->init_layout.size;
> + return within_module_init((unsigned long)loc, mod);
> }
Wouldn't it make sense to get rid of these indirections in arm[64]
completely ?
> struct mod_kallsyms {
> @@ -418,12 +448,8 @@ struct module {
> /* Startup function. */
> int (*init)(void);
>
> - /* Core layout: rbtree is accessed frequently, so keep together. */
> - struct module_layout core_layout __module_layout_align;
> - struct module_layout init_layout;
> -#ifdef CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC
> - struct module_layout data_layout;
> -#endif
> + /* rbtree is accessed frequently, so keep together. */
I'm confused about the rbtree comment here.
> + struct module_memory mem[MOD_MEM_NUM_TYPES] __module_memory_align;
>
> /* Arch-specific module values */
> struct mod_arch_specific arch;
> @@ -573,23 +599,33 @@ bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr);
> bool is_module_percpu_address(unsigned long addr);
> bool is_module_text_address(unsigned long addr);
>
> +static inline bool within_module_mem_type(unsigned long addr,
> + const struct module *mod,
> + enum mod_mem_type type)
> +{
> + unsigned long base, size;
> +
> + base = (unsigned long)mod->mem[type].base;
> + size = mod->mem[type].size;
> + return addr - base < size;
> +}
> +
> static inline bool within_module_core(unsigned long addr,
> const struct module *mod)
> {
> -#ifdef CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC
> - if ((unsigned long)mod->data_layout.base <= addr &&
> - addr < (unsigned long)mod->data_layout.base + mod->data_layout.size)
> - return true;
> -#endif
> - return (unsigned long)mod->core_layout.base <= addr &&
> - addr < (unsigned long)mod->core_layout.base + mod->core_layout.size;
> + for_class_mod_mem_type(type, core)
> + if (within_module_mem_type(addr, mod, type))
> + return true;
for_class_mod_mem_type(type, core) {
if (within_module_mem_type(addr, mod, type))
return true;
}
Please. It's not required by the language, but it makes the code simpler
to read. We omit the brackets when there is a true one-line statement
after the iterator() or condition().
> +static void free_mod_mem(struct module *mod)
> +{
> + /* free the memory in the right order to avoid use-after-free */
How do we end up with a UAF when the ordering is different?
> + static enum mod_mem_type mod_mem_free_order[MOD_MEM_NUM_TYPES] = {
> + /* first free init sections */
> + MOD_INIT_TEXT,
> + MOD_INIT_DATA,
> + MOD_INIT_RODATA,
> +
> + /* then core sections, except rw data */
> + MOD_TEXT,
> + MOD_RODATA,
> + MOD_RO_AFTER_INIT,
> +
> + /* last, rw data */
> + MOD_DATA,
> + };
That's fragile when we ever add a new section type.
static const enum mod_mem_type mod_mem_free_order[] = {
....
};
BUILD_BUG_ON(ARRAY_SIZE(mod_mem_free_order) != MOD_MEM_NUM_TYPES);
Hmm?
>
> static bool module_init_layout_section(const char *sname)
> @@ -1428,6 +1506,20 @@ static void layout_sections(struct module *mod, struct load_info *info)
> { SHF_WRITE | SHF_ALLOC, ARCH_SHF_SMALL },
> { ARCH_SHF_SMALL | SHF_ALLOC, 0 }
> };
> + static int core_m_to_mem_type[] = {
const?
> + MOD_TEXT,
> + MOD_RODATA,
> + MOD_RO_AFTER_INIT,
> + MOD_DATA,
> + MOD_INVALID,
What's the point of this MOD_INVALID here?
> + };
> + static int init_m_to_mem_type[] = {
> + MOD_INIT_TEXT,
> + MOD_INIT_RODATA,
> + MOD_INVALID,
> + MOD_INIT_DATA,
> + MOD_INVALID,
> + };
> unsigned int m, i;
>
> for (i = 0; i < info->hdr->e_shnum; i++)
> @@ -1435,41 +1527,30 @@ static void layout_sections(struct module *mod, struct load_info *info)
>
> pr_debug("Core section allocation order:\n");
> for (m = 0; m < ARRAY_SIZE(masks); ++m) {
> + enum mod_mem_type type = core_m_to_mem_type[m];
Oh. This deals with ARRAY_SIZE(masks) being larger than the
*_to_mem_type[] ones. A comment on the *to_mem_type arrays would be
appreciated.
>
> pr_debug("Init section allocation order:\n");
> for (m = 0; m < ARRAY_SIZE(masks); ++m) {
> + enum mod_mem_type type = init_m_to_mem_type[m];
> +
> for (i = 0; i < info->hdr->e_shnum; ++i) {
> Elf_Shdr *s = &info->sechdrs[i];
> const char *sname = info->secstrings + s->sh_name;
> @@ -1479,30 +1560,13 @@ static void layout_sections(struct module *mod, struct load_info *info)
> || s->sh_entsize != ~0UL
> || !module_init_layout_section(sname))
> continue;
> - s->sh_entsize = (module_get_offset(mod, &mod->init_layout.size, s, i)
> - | INIT_OFFSET_MASK);
> +
> + if (WARN_ON_ONCE(type == MOD_INVALID))
> + continue;
> +
> + s->sh_entsize = module_get_offset_and_type(mod, type, s, i);
> pr_debug("\t%s\n", sname);
Now that the explicit layout members are gone the only difference
between the core and the init part aside of the seperate _to_mem_type[]
array is:
- || module_init_layout_section(sname))
+ || !module_init_layout_section(sname))
continue;
Which means the loop can be moved into a separate function which takes
an @is_init argument which then selects the right _to_mem_type[] array
and tweaks the condition accordingly. Can be a follow up patch.
> + for_each_mod_mem_type(type) {
> + const struct module_memory *mod_mem = &mod->mem[type];
> +
> + if (mod_mem->size)
> + flush_icache_range((unsigned long)mod_mem->base,
> + (unsigned long)mod_mem->base + mod_mem->size);
Brackets here too, please
> diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
> index 14fbea66f12f..2e79a77f40eb 100644
> --- a/kernel/module/strict_rwx.c
> +++ b/kernel/module/strict_rwx.c
> @@ -11,82 +11,26 @@
> #include <linux/set_memory.h>
> #include "internal.h"
>
> -/*
> - * LKM RO/NX protection: protect module's text/ro-data
> - * from modification and any data from execution.
> - *
> - * General layout of module is:
> - * [text] [read-only-data] [ro-after-init] [writable data]
> - * text_size -----^ ^ ^ ^
> - * ro_size ------------------------| | |
> - * ro_after_init_size -----------------------------| |
> - * size -----------------------------------------------------------|
> - *
> - * These values are always page-aligned (as is base) when
> - * CONFIG_STRICT_MODULE_RWX is set.
> - */
> +static void module_set_memory(
> + const struct module *mod, enum mod_mem_type type,
> + int (*set_memory)(unsigned long start, int num_pages))
Please don't use this horrible formatting.
static void module_set_memory(const struct module *mod, enum mod_mem_type type,
int (*set_memory)(unsigned long start, int num_pages))
We lifted the 80 character limit long ago.
> +{
> + const struct module_memory *mod_mem = &mod->mem[type];
Other than those nits, this looks great!
Thanks,
tglx
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