Re: [PATCH] RISC-V: Fix FIXMAP area corruption on RV32 systems

[Alistair Francis]

On Fri, 2019-08-16 at 11:49 +0000, Anup Patel wrote:
> Currently, the order of various virtual memory areas in increasing
> order of virtual addresses is as follows:
> 1. User space area
> 2. FIXMAP area
> 3. VMALLOC area
> 4. Kernel area
> 
> The user space area starts at 0x0 and it's maximum size 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. 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.patel@xxxxxxx>

This fixes the RV32 issue.

Tested-by: Alistair Francis <alistair.francis@xxxxxxx>

Alistair

> ---
>  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..9dd08a006a28 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>