Re: [PATCH v3 01/13] riscv: Move KASAN mapping next to the kernel mapping

[Jisheng Zhang <jszhang@kernel.org>]

On Mon,  6 Dec 2021 11:46:45 +0100
Alexandre Ghiti <alexandre.ghiti@canonical.com> wrote:

> Now that KASAN_SHADOW_OFFSET is defined at compile time as a config,
> this value must remain constant whatever the size of the virtual address
> space, which is only possible by pushing this region at the end of the
> address space next to the kernel mapping.
> 
> Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
> ---
>  Documentation/riscv/vm-layout.rst | 12 ++++++------
>  arch/riscv/Kconfig                |  4 ++--
>  arch/riscv/include/asm/kasan.h    |  4 ++--
>  arch/riscv/include/asm/page.h     |  6 +++++-
>  arch/riscv/include/asm/pgtable.h  |  6 ++++--
>  arch/riscv/mm/init.c              | 25 +++++++++++++------------
>  6 files changed, 32 insertions(+), 25 deletions(-)
> 
> diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst
> index b7f98930d38d..1bd687b97104 100644
> --- a/Documentation/riscv/vm-layout.rst
> +++ b/Documentation/riscv/vm-layout.rst
> @@ -47,12 +47,12 @@ RISC-V Linux Kernel SV39
>                                                                | Kernel-space virtual memory, shared between all processes:
>    ____________________________________________________________|___________________________________________________________
>                      |            |                  |         |
> -   ffffffc000000000 | -256    GB | ffffffc7ffffffff |   32 GB | kasan
> -   ffffffcefee00000 | -196    GB | ffffffcefeffffff |    2 MB | fixmap
> -   ffffffceff000000 | -196    GB | ffffffceffffffff |   16 MB | PCI io
> -   ffffffcf00000000 | -196    GB | ffffffcfffffffff |    4 GB | vmemmap
> -   ffffffd000000000 | -192    GB | ffffffdfffffffff |   64 GB | vmalloc/ioremap space
> -   ffffffe000000000 | -128    GB | ffffffff7fffffff |  124 GB | direct mapping of all physical memory
> +   ffffffc6fee00000 | -228    GB | ffffffc6feffffff |    2 MB | fixmap
> +   ffffffc6ff000000 | -228    GB | ffffffc6ffffffff |   16 MB | PCI io
> +   ffffffc700000000 | -228    GB | ffffffc7ffffffff |    4 GB | vmemmap
> +   ffffffc800000000 | -224    GB | ffffffd7ffffffff |   64 GB | vmalloc/ioremap space
> +   ffffffd800000000 | -160    GB | fffffff6ffffffff |  124 GB | direct mapping of all physical memory
> +   fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
>    __________________|____________|__________________|_________|____________________________________________________________
>                                                                |
>                                                                |
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 6d5b63bd4bd9..6cd98ade5ebc 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -161,12 +161,12 @@ config PAGE_OFFSET
>  	default 0xC0000000 if 32BIT && MAXPHYSMEM_1GB
>  	default 0x80000000 if 64BIT && !MMU
>  	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
> -	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
> +	default 0xffffffd800000000 if 64BIT && MAXPHYSMEM_128GB
>  
>  config KASAN_SHADOW_OFFSET
>  	hex
>  	depends on KASAN_GENERIC
> -	default 0xdfffffc800000000 if 64BIT
> +	default 0xdfffffff00000000 if 64BIT
>  	default 0xffffffff if 32BIT
>  
>  config ARCH_FLATMEM_ENABLE
> diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
> index b00f503ec124..257a2495145a 100644
> --- a/arch/riscv/include/asm/kasan.h
> +++ b/arch/riscv/include/asm/kasan.h
> @@ -28,8 +28,8 @@
>  #define KASAN_SHADOW_SCALE_SHIFT	3
>  
>  #define KASAN_SHADOW_SIZE	(UL(1) << ((CONFIG_VA_BITS - 1) - KASAN_SHADOW_SCALE_SHIFT))
> -#define KASAN_SHADOW_START	KERN_VIRT_START
> -#define KASAN_SHADOW_END	(KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
> +#define KASAN_SHADOW_START	(KASAN_SHADOW_END - KASAN_SHADOW_SIZE)
> +#define KASAN_SHADOW_END	MODULES_LOWEST_VADDR
>  #define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>  
>  void kasan_init(void);
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 109c97e991a6..e03559f9b35e 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -33,7 +33,11 @@
>   */
>  #define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
>  
> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
> +/*
> + * Half of the kernel address space (half of the entries of the page global
> + * directory) is for the direct mapping.
> + */
> +#define KERN_VIRT_SIZE		((PTRS_PER_PGD / 2 * PGDIR_SIZE) / 2)
>  
>  #ifndef __ASSEMBLY__
>  
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 39b550310ec6..d34f3a7a9701 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -39,8 +39,10 @@
>  
>  /* Modules always live before the kernel */
>  #ifdef CONFIG_64BIT
> -#define MODULES_VADDR	(PFN_ALIGN((unsigned long)&_end) - SZ_2G)
> -#define MODULES_END	(PFN_ALIGN((unsigned long)&_start))
> +/* This is used to define the end of the KASAN shadow region */
> +#define MODULES_LOWEST_VADDR	(KERNEL_LINK_ADDR - SZ_2G)
> +#define MODULES_VADDR		(PFN_ALIGN((unsigned long)&_end) - SZ_2G)
> +#define MODULES_END		(PFN_ALIGN((unsigned long)&_start))
>  #endif
>  
>  /*
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index c0cddf0fc22d..4224e9d0ecf5 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -103,6 +103,9 @@ static void __init print_vm_layout(void)
>  	print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
>  		  (unsigned long)high_memory);
>  #ifdef CONFIG_64BIT
> +#ifdef CONFIG_KASAN
> +	print_mlm("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);
> +#endif

I think we'd better avoid #ifdef usage as much as possible.
For this KASAN case, we can make both KASAN_SHADOW_START and KASAN_SHADOW_END
always visible as x86 does, then above code can be
if (IS_ENABLED(CONFIG_KASAN))
	print_mlm("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);

Thanks