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

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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@xxxxxxxxxx>
> ---
>   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;
> +}




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