Hello Anup,
On Mon, 19 Aug 2019, Anup Patel wrote:
> Currently, various virtual memory areas of Linux RISC-V are organized
> in increasing order of their virtual addresses is as follows:
> 1. User space area (This is lowest area and starts at 0x0)
> 2. FIXMAP area
> 3. VMALLOC area
> 4. Kernel area (This is highest area and starts at PAGE_OFFSET)
>
> The maximum size of user space aread is represented by TASK_SIZE.
>
> On RV32 systems, TASK_SIZE is defined as VMALLOC_START which causes the
> user space area to overlap the FIXMAP area. This allows user space apps
> to potentially corrupt the FIXMAP area and kernel OF APIs will crash
> whenever they access corrupted FDT in the FIXMAP area.
>
> On RV64 systems, TASK_SIZE is set to fixed 256GB and no other areas
> happen to overlap so we don't see any FIXMAP area corruptions.
>
> This patch fixes FIXMAP area corruption on RV32 systems by setting
> TASK_SIZE to FIXADDR_START.
This part -- the TASK_SIZE change -- makes sense to me.
However, the patch also changes FIXADDR_SIZE to be defined in terms of
page table-related constants. Previously, FIXADDR_SIZE was based on
__end_of_fixed_addresses, as it is for most other architectures. The part
of the patch that changes FIXADDR_SIZE seems unrelated to the actual fix.
If that's indeed the case -- that the change to FIXADDR_SIZE is unrelated
from the fix -- could you please split that into a separate patch, with a
description of the rationale? I think I understand why you're proposing
it, but it seems odd to explicitly connect it to page table-related
constants, rather than the contents of "enum fixed_addresses", and I'm
reluctant to merge that part of this patch without a bit more discussion.
> We also move FIXADDR_TOP, FIXADDR_SIZE, and FIXADDR_START defines to
> asm/pgtable.h so that we can avoid cyclic header includes.
>
> Signed-off-by: Anup Patel <anup.pa...@wdc.com>
> Tested-by: Alistair Francis <alistair.fran...@wdc.com>
> Reviewed-by: Christoph Hellwig <h...@lst.de>
> ---
> Changes since v1:
> - Drop braces from "#define FIXADDR_TOP"
> ---
> arch/riscv/include/asm/fixmap.h | 4 ----
> arch/riscv/include/asm/pgtable.h | 12 ++++++++++--
> 2 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index 9c66033c3a54..161f28d04a07 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -30,10 +30,6 @@ enum fixed_addresses {
> __end_of_fixed_addresses
> };
>
> -#define FIXADDR_SIZE (__end_of_fixed_addresses * PAGE_SIZE)
> -#define FIXADDR_TOP (VMALLOC_START)
> -#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
> -
> #define FIXMAP_PAGE_IO PAGE_KERNEL
>
> #define __early_set_fixmap __set_fixmap
> diff --git a/arch/riscv/include/asm/pgtable.h
> b/arch/riscv/include/asm/pgtable.h
> index a364aba23d55..c24a083b3e12 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -420,14 +420,22 @@ static inline void pgtable_cache_init(void)
> #define VMALLOC_END (PAGE_OFFSET - 1)
> #define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
>
> +#define FIXADDR_TOP VMALLOC_START
> +#ifdef CONFIG_64BIT
> +#define FIXADDR_SIZE PMD_SIZE
> +#else
> +#define FIXADDR_SIZE PGDIR_SIZE
> +#endif
> +#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
> +
> /*
> - * Task size is 0x4000000000 for RV64 or 0xb800000 for RV32.
> + * Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
> * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> */
> #ifdef CONFIG_64BIT
> #define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)
> #else
> -#define TASK_SIZE VMALLOC_START
> +#define TASK_SIZE FIXADDR_START
> #endif
>
> #include <asm-generic/pgtable.h>
> --
> 2.17.1
>
- Paul
