linux-kernel - Re: [PATCH 10/13] powerpc: Define KMSAN metadata address ranges for vmalloc and ioremap

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Date:   Thu, 14 Dec 2023 09:17:30 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
        "glider@...gle.com" <glider@...gle.com>,
        "elver@...gle.com" <elver@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "iii@...ux.ibm.com" <iii@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/13] powerpc: Define KMSAN metadata address ranges for
 vmalloc and ioremap



Le 14/12/2023 à 06:55, Nicholas Miehlbradt a écrit :
> Splits the vmalloc region into four. The first quarter is the new
> vmalloc region, the second is used to store shadow metadata and the
> third is used to store origin metadata. The fourth quarter is unused.
> 
> Do the same for the ioremap region.
> 
> Module data is stored in the vmalloc region so alias the modules
> metadata addresses to the respective vmalloc metadata addresses. Define
> MODULES_VADDR and MODULES_END to the start and end of the vmalloc
> region.
> 
> Since MODULES_VADDR was previously only defined on ppc32 targets checks
> for if this macro is defined need to be updated to include
> defined(CONFIG_PPC32).

Why ?

In your case MODULES_VADDR is above PAGE_OFFSET so there should be no 
difference.

Christophe

> 
> Signed-off-by: Nicholas Miehlbradt <nicholas@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 42 ++++++++++++++++++++
>   arch/powerpc/kernel/module.c                 |  2 +-
>   2 files changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index cb77eddca54b..b3a02b8d96e3 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -249,7 +249,38 @@ enum pgtable_index {
>   extern unsigned long __vmalloc_start;
>   extern unsigned long __vmalloc_end;
>   #define VMALLOC_START	__vmalloc_start
> +
> +#ifndef CONFIG_KMSAN
>   #define VMALLOC_END	__vmalloc_end
> +#else
> +/*
> + * In KMSAN builds vmalloc area is four times smaller, and the remaining 3/4
> + * are used to keep the metadata for virtual pages. The memory formerly
> + * belonging to vmalloc area is now laid out as follows:
> + *
> + * 1st quarter: VMALLOC_START to VMALLOC_END - new vmalloc area
> + * 2nd quarter: KMSAN_VMALLOC_SHADOW_START to
> + *              KMSAN_VMALLOC_SHADOW_START+VMALLOC_LEN - vmalloc area shadow
> + * 3rd quarter: KMSAN_VMALLOC_ORIGIN_START to
> + *              KMSAN_VMALLOC_ORIGIN_START+VMALLOC_LEN - vmalloc area origins
> + * 4th quarter: unused
> + */
> +#define VMALLOC_LEN ((__vmalloc_end - __vmalloc_start) >> 2)
> +#define VMALLOC_END (VMALLOC_START + VMALLOC_LEN)
> +
> +#define KMSAN_VMALLOC_SHADOW_START VMALLOC_END
> +#define KMSAN_VMALLOC_ORIGIN_START (VMALLOC_END + VMALLOC_LEN)
> +
> +/*
> + * Module metadata is stored in the corresponding vmalloc metadata regions
> + */
> +#define KMSAN_MODULES_SHADOW_START	KMSAN_VMALLOC_SHADOW_START
> +#define KMSAN_MODULES_ORIGIN_START	KMSAN_VMALLOC_ORIGIN_START
> +#endif /* CONFIG_KMSAN */
> +
> +#define MODULES_VADDR VMALLOC_START
> +#define MODULES_END VMALLOC_END
> +#define MODULES_LEN		(MODULES_END - MODULES_VADDR)
>   
>   static inline unsigned int ioremap_max_order(void)
>   {
> @@ -264,7 +295,18 @@ extern unsigned long __kernel_io_start;
>   extern unsigned long __kernel_io_end;
>   #define KERN_VIRT_START __kernel_virt_start
>   #define KERN_IO_START  __kernel_io_start
> +#ifndef CONFIG_KMSAN
>   #define KERN_IO_END __kernel_io_end
> +#else
> +/*
> + * In KMSAN builds IO space is 4 times smaller, the remaining space is used to
> + * store metadata. See comment for vmalloc regions above.
> + */
> +#define KERN_IO_LEN             ((__kernel_io_end - __kernel_io_start) >> 2)
> +#define KERN_IO_END             (KERN_IO_START + KERN_IO_LEN)
> +#define KERN_IO_SHADOW_START    KERN_IO_END
> +#define KERN_IO_ORIGIN_START    (KERN_IO_SHADOW_START + KERN_IO_LEN)
> +#endif /* !CONFIG_KMSAN */
>   
>   extern struct page *vmemmap;
>   extern unsigned long pci_io_base;
> diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> index f6d6ae0a1692..5043b959ad4d 100644
> --- a/arch/powerpc/kernel/module.c
> +++ b/arch/powerpc/kernel/module.c
> @@ -107,7 +107,7 @@ __module_alloc(unsigned long size, unsigned long start, unsigned long end, bool
>   
>   void *module_alloc(unsigned long size)
>   {
> -#ifdef MODULES_VADDR
> +#if defined(MODULES_VADDR) && defined(CONFIG_PPC32)
>   	unsigned long limit = (unsigned long)_etext - SZ_32M;
>   	void *ptr = NULL;
>