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Subject: Re: [PATCH v11 3/9] powerpc: Always define MODULES_{VADDR,END}
To: Jordan Niethe <jniethe5@gmail.com>, linuxppc-dev@lists.ozlabs.org
References: <20210429031602.2606654-1-jniethe5@gmail.com>
 <20210429031602.2606654-4-jniethe5@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Thu, 29 Apr 2021 07:04:08 +0200
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Le 29/04/2021 à 05:15, Jordan Niethe a écrit :
> If MODULES_{VADDR,END} are not defined set them to VMALLOC_START and
> VMALLOC_END respectively. This reduces the need for special cases. For
> example, powerpc's module_alloc() was previously predicated on
> MODULES_VADDR being defined but now is unconditionally defined.
> 
> This will be useful reducing conditional code in other places that need
> to allocate from the module region (i.e., kprobes).
> 
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
> v10: New to series
> v11: - Consider more places MODULES_VADDR was being used
> ---
>   arch/powerpc/include/asm/pgtable.h    | 11 +++++++++++
>   arch/powerpc/kernel/module.c          |  5 +----
>   arch/powerpc/mm/kasan/kasan_init_32.c | 10 +++++-----
>   arch/powerpc/mm/ptdump/ptdump.c       |  4 ++--
>   4 files changed, 19 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index c6a676714f04..882fda779648 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -39,6 +39,17 @@ struct mm_struct;
>   #define __S110	PAGE_SHARED_X
>   #define __S111	PAGE_SHARED_X
>   
> +#ifndef MODULES_VADDR
> +#define MODULES_VADDR VMALLOC_START
> +#define MODULES_END VMALLOC_END
> +#endif
> +
> +#if defined(CONFIG_PPC_BOOK3S_32) && defined(CONFIG_STRICT_KERNEL_RWX)

No no.

TASK_SIZE > MODULES_VADDR is ALWAYS wrong, for any target, in any configuration.

Why is it a problem to leave the test as a BUILD_BUG_ON() in module_alloc() ?

> +#if TASK_SIZE > MODULES_VADDR
> +#error TASK_SIZE > MODULES_VADDR
> +#endif
> +#endif
> +
>   #ifndef __ASSEMBLY__
>   
>   /* Keep these as a macros to avoid include dependency mess */
> diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> index fab84024650c..c60c7457ff47 100644
> --- a/arch/powerpc/kernel/module.c
> +++ b/arch/powerpc/kernel/module.c
> @@ -15,6 +15,7 @@
>   #include <linux/sort.h>
>   #include <asm/setup.h>
>   #include <asm/sections.h>
> +#include <linux/mm.h>
>   
>   static LIST_HEAD(module_bug_list);
>   
> @@ -88,7 +89,6 @@ int module_finalize(const Elf_Ehdr *hdr,
>   	return 0;
>   }
>   
> -#ifdef MODULES_VADDR
>   static __always_inline void *
>   __module_alloc(unsigned long size, unsigned long start, unsigned long end)
>   {
> @@ -102,8 +102,6 @@ void *module_alloc(unsigned long size)
>   	unsigned long limit = (unsigned long)_etext - SZ_32M;
>   	void *ptr = NULL;
>   
> -	BUILD_BUG_ON(TASK_SIZE > MODULES_VADDR);
> -
>   	/* First try within 32M limit from _etext to avoid branch trampolines */
>   	if (MODULES_VADDR < PAGE_OFFSET && MODULES_END > limit)
>   		ptr = __module_alloc(size, limit, MODULES_END);
> @@ -113,4 +111,3 @@ void *module_alloc(unsigned long size)
>   
>   	return ptr;
>   }
> -#endif
> diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
> index cf8770b1a692..42c057366ac7 100644
> --- a/arch/powerpc/mm/kasan/kasan_init_32.c
> +++ b/arch/powerpc/mm/kasan/kasan_init_32.c
> @@ -116,11 +116,11 @@ static void __init kasan_unmap_early_shadow_vmalloc(void)
>   
>   	kasan_update_early_region(k_start, k_end, __pte(0));
>   
> -#ifdef MODULES_VADDR
> -	k_start = (unsigned long)kasan_mem_to_shadow((void *)MODULES_VADDR);
> -	k_end = (unsigned long)kasan_mem_to_shadow((void *)MODULES_END);
> -	kasan_update_early_region(k_start, k_end, __pte(0));
> -#endif
> +	if (MODULES_VADDR != VMALLOC_START && MODULES_END != VMALLOC_END) {

Shouldn't it be an || ?

As soon as either MODULES_VADDR or MODULES_END differs from the vmalloc boundaries, it needs to be 
done I think.

> +		k_start = (unsigned long)kasan_mem_to_shadow((void *)MODULES_VADDR);
> +		k_end = (unsigned long)kasan_mem_to_shadow((void *)MODULES_END);
> +		kasan_update_early_region(k_start, k_end, __pte(0));
> +	}
>   }
>   
>   void __init kasan_mmu_init(void)
> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
> index aca354fb670b..0431457f668f 100644
> --- a/arch/powerpc/mm/ptdump/ptdump.c
> +++ b/arch/powerpc/mm/ptdump/ptdump.c
> @@ -73,7 +73,7 @@ struct addr_marker {
>   
>   static struct addr_marker address_markers[] = {
>   	{ 0,	"Start of kernel VM" },
> -#ifdef MODULES_VADDR
> +#if defined(CONFIG_BOOK32_32) && defined(CONFIG_STRICT_KERNEL_RWX)

Not valid anymore, see https://github.com/linuxppc/linux/commit/80edc68e0479 and 
https://github.com/linuxppc/linux/commit/9132a2e82adc

The best would be to be able to do something like:

#if MODULES_VADDR != VMALLOC_START

If it doesn't work, then it has to be

#if defined(CONFIG_BOOK32_32) || defined(CONFIG_PPC_8xx)

>   	{ 0,	"modules start" },
>   	{ 0,	"modules end" },
>   #endif
> @@ -359,7 +359,7 @@ static void populate_markers(void)
>   #else
>   	address_markers[i++].start_address = TASK_SIZE;
>   #endif
> -#ifdef MODULES_VADDR
> +#if defined(CONFIG_BOOK32_32) && defined(CONFIG_STRICT_KERNEL_RWX)

Same.

>   	address_markers[i++].start_address = MODULES_VADDR;
>   	address_markers[i++].start_address = MODULES_END;
>   #endif
>