Re: [PATCH v5 06/13] module: Move strict rwx support to a separate file

Christophe Leroy
2022-02-10T12:21:55Z

Le 09/02/2022 à 18:03, Aaron Tomlin a écrit :
> No functional change.
>
> This patch migrates code that makes module text
> and rodata memory read-only and non-text memory
> non-executable from core module code into
> kernel/module/strict_rwx.c.
>
> Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
> ---
> kernel/module/Makefile | 1 +
> kernel/module/internal.h | 38 +++++++++++++++
> kernel/module/main.c | 97 +-------------------------------------
> kernel/module/strict_rwx.c | 84 +++++++++++++++++++++++++++++++++

This file generates many checkpatch WARNINGs and CHECKs.

Don't worry too much about the ones telling you to use WARN_ON() instead
of BUG_ON() for the time being, but others should be handled.

> 4 files changed, 124 insertions(+), 96 deletions(-)
> create mode 100644 kernel/module/strict_rwx.c
>
> diff --git a/kernel/module/Makefile b/kernel/module/Makefile
> index fc6d7a053a62..8f2857d9ba1e 100644
> --- a/kernel/module/Makefile
> +++ b/kernel/module/Makefile
> @@ -10,4 +10,5 @@ obj-$(CONFIG_MODULE_SIG_FORMAT) += signature.o
> ifdef CONFIG_MODULES
> obj-$(CONFIG_LIVEPATCH) += livepatch.o
> obj-$(CONFIG_MODULES_TREE_LOOKUP) += tree_lookup.o
> +obj-$(CONFIG_STRICT_MODULE_RWX) += strict_rwx.o
> endif
> diff --git a/kernel/module/internal.h b/kernel/module/internal.h
> index 08b6be037b72..99204447ce86 100644
> --- a/kernel/module/internal.h
> +++ b/kernel/module/internal.h
> @@ -21,6 +21,17 @@
> #define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4)
> #define MODULE_SECT_READ_SIZE (3 /* "0x", "\n" */ + (BITS_PER_LONG / 4))
>
> +/*
> + * Modules' sections will be aligned on page boundaries
> + * to ensure complete separation of code and data, but
> + * only when CONFIG_ARCH_HAS_STRICT_MODULE_RWX=y
> + */
> +#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
> +# define debug_align(X) ALIGN(X, PAGE_SIZE)

You can use PAGE_ALIGN() instead.

> +#else
> +# define debug_align(X) (X)
> +#endif
> +
> extern struct mutex module_mutex;
> extern struct list_head modules;
>
> @@ -124,3 +135,30 @@ static struct module *mod_find(unsigned long addr)
> return NULL;
> }
> #endif /* CONFIG_MODULES_TREE_LOOKUP */
> +
> +#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX

This #ifdef is not needed, frob_text() always exists.

> +void frob_text(const struct module_layout *layout, int (*set_memory)(unsigned long start,
> + int num_pages));
> +#endif /* CONFIG_ARCH_HAS_STRICT_MODULE_RWX */
> +
> +#ifdef CONFIG_STRICT_MODULE_RWX
> +void frob_rodata(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages));
> +void frob_ro_after_init(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages));
> +void frob_writable_data(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages));
> +void module_enable_ro(const struct module *mod, bool after_init);
> +void module_enable_nx(const struct module *mod);
> +int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> + char *secstrings, struct module *mod);
> +
> +#else /* !CONFIG_STRICT_MODULE_RWX */
> +static void module_enable_nx(const struct module *mod) { }
> +static void module_enable_ro(const struct module *mod, bool after_init) {}
> +static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> + char *secstrings, struct module *mod)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_STRICT_MODULE_RWX */
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index f733a719c65d..abdedc15f4f1 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -63,17 +63,6 @@
> #define CREATE_TRACE_POINTS
> #include <trace/events/module.h>
>
> -/*
> - * Modules' sections will be aligned on page boundaries
> - * to ensure complete separation of code and data, but
> - * only when CONFIG_ARCH_HAS_STRICT_MODULE_RWX=y
> - */
> -#ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
> -# define debug_align(X) ALIGN(X, PAGE_SIZE)
> -#else
> -# define debug_align(X) (X)
> -#endif
> -
> /*
> * Mutex protects:
> * 1) List of modules (also safely readable with preempt_disable),
> @@ -1815,7 +1804,7 @@ static void mod_sysfs_teardown(struct module *mod)
> * whether we are strict.
> */
> #ifdef CONFIG_ARCH_HAS_STRICT_MODULE_RWX
> -static void frob_text(const struct module_layout *layout,
> +void frob_text(const struct module_layout *layout,
> int (*set_memory)(unsigned long start, int num_pages))

The alignment of the second line is not correct.

> {
> BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> @@ -1833,90 +1822,6 @@ static void module_enable_x(const struct module *mod)
> static void module_enable_x(const struct module *mod) { }
> #endif /* CONFIG_ARCH_HAS_STRICT_MODULE_RWX */
>
> -#ifdef CONFIG_STRICT_MODULE_RWX
> -static void frob_rodata(const struct module_layout *layout,
> - int (*set_memory)(unsigned long start, int num_pages))
> -{
> - BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
> - set_memory((unsigned long)layout->base + layout->text_size,
> - (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
> -}
> -
> -static void frob_ro_after_init(const struct module_layout *layout,
> - int (*set_memory)(unsigned long start, int num_pages))
> -{
> - BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
> - set_memory((unsigned long)layout->base + layout->ro_size,
> - (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
> -}
> -
> -static void frob_writable_data(const struct module_layout *layout,
> - int (*set_memory)(unsigned long start, int num_pages))
> -{
> - BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
> - BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1));
> - set_memory((unsigned long)layout->base + layout->ro_after_init_size,
> - (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
> -}
> -
> -static void module_enable_ro(const struct module *mod, bool after_init)
> -{
> - if (!rodata_enabled)
> - return;
> -
> - set_vm_flush_reset_perms(mod->core_layout.base);
> - set_vm_flush_reset_perms(mod->init_layout.base);
> - frob_text(&mod->core_layout, set_memory_ro);
> -
> - frob_rodata(&mod->core_layout, set_memory_ro);
> - frob_text(&mod->init_layout, set_memory_ro);
> - frob_rodata(&mod->init_layout, set_memory_ro);
> -
> - if (after_init)
> - frob_ro_after_init(&mod->core_layout, set_memory_ro);
> -}
> -
> -static void module_enable_nx(const struct module *mod)
> -{
> - frob_rodata(&mod->core_layout, set_memory_nx);
> - frob_ro_after_init(&mod->core_layout, set_memory_nx);
> - frob_writable_data(&mod->core_layout, set_memory_nx);
> - frob_rodata(&mod->init_layout, set_memory_nx);
> - frob_writable_data(&mod->init_layout, set_memory_nx);
> -}
> -
> -static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> - char *secstrings, struct module *mod)
> -{
> - const unsigned long shf_wx = SHF_WRITE|SHF_EXECINSTR;
> - int i;
> -
> - for (i = 0; i < hdr->e_shnum; i++) {
> - if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
> - pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
> - mod->name, secstrings + sechdrs[i].sh_name, i);
> - return -ENOEXEC;
> - }
> - }
> -
> - return 0;
> -}
> -
> -#else /* !CONFIG_STRICT_MODULE_RWX */
> -static void module_enable_nx(const struct module *mod) { }
> -static void module_enable_ro(const struct module *mod, bool after_init) {}
> -static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> - char *secstrings, struct module *mod)
> -{
> - return 0;
> -}
> -#endif /* CONFIG_STRICT_MODULE_RWX */
> -
> void __weak module_memfree(void *module_region)
> {
> /*
> diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
> new file mode 100644
> index 000000000000..1933272056c7
> --- /dev/null
> +++ b/kernel/module/strict_rwx.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Module strict rwx
> + *
> + * Copyright (C) 2015 Rusty Russell
> + */
> +
> +#include <linux/module.h>
> +#include <linux/vmalloc.h>
> +#include <linux/set_memory.h>
> +#include "internal.h"
> +
> +void frob_rodata(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages))
> +{
> + BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));

Could be:

BUG_ON(!PAGE_ALIGNED(layout->base));

Same for all others.

> + BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
> + BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
> + set_memory((unsigned long)layout->base + layout->text_size,
> + (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
> +}
> +
> +void frob_ro_after_init(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages))
> +{
> + BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> + BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
> + BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
> + set_memory((unsigned long)layout->base + layout->ro_size,
> + (layout->ro_after_init_size - layout->ro_size) >> PAGE_SHIFT);
> +}
> +
> +void frob_writable_data(const struct module_layout *layout,
> + int (*set_memory)(unsigned long start, int num_pages))
> +{
> + BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
> + BUG_ON((unsigned long)layout->ro_after_init_size & (PAGE_SIZE-1));
> + BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1));
> + set_memory((unsigned long)layout->base + layout->ro_after_init_size,
> + (layout->size - layout->ro_after_init_size) >> PAGE_SHIFT);
> +}
> +
> +void module_enable_ro(const struct module *mod, bool after_init)
> +{
> + if (!rodata_enabled)
> + return;
> +
> + set_vm_flush_reset_perms(mod->core_layout.base);
> + set_vm_flush_reset_perms(mod->init_layout.base);
> + frob_text(&mod->core_layout, set_memory_ro);
> +
> + frob_rodata(&mod->core_layout, set_memory_ro);
> + frob_text(&mod->init_layout, set_memory_ro);
> + frob_rodata(&mod->init_layout, set_memory_ro);
> +
> + if (after_init)
> + frob_ro_after_init(&mod->core_layout, set_memory_ro);
> +}
> +
> +void module_enable_nx(const struct module *mod)
> +{
> + frob_rodata(&mod->core_layout, set_memory_nx);
> + frob_ro_after_init(&mod->core_layout, set_memory_nx);
> + frob_writable_data(&mod->core_layout, set_memory_nx);
> + frob_rodata(&mod->init_layout, set_memory_nx);
> + frob_writable_data(&mod->init_layout, set_memory_nx);
> +}
> +
> +int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> + char *secstrings, struct module *mod)
> +{
> + const unsigned long shf_wx = SHF_WRITE|SHF_EXECINSTR;
> + int i;
> +
> + for (i = 0; i < hdr->e_shnum; i++) {
> + if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
> + pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
> + mod->name, secstrings + sechdrs[i].sh_name, i);
> + return -ENOEXEC;
> + }
> + }
> +
> + return 0;
> +}