Re: [PATCH v2 3/6] RISC-V: Enforce protections for kernel sections early

Mike Rapoport
2020-10-27T10:00:54Z

On Mon, Oct 26, 2020 at 04:02:51PM -0700, Atish Patra wrote:
> Currently, all memblocks are mapped with PAGE_KERNEL_EXEC and the strict
> permissions are only enforced after /init starts. This leaves the kernel
> vulnerable from possible buggy built-in modules.
>
> Apply permissions to individual sections as early as possible.
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
> arch/riscv/include/asm/set_memory.h | 2 ++
> arch/riscv/kernel/setup.c | 2 ++
> arch/riscv/mm/init.c | 11 +++++++++--
> 3 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index 4c5bae7ca01c..4cc3a4e2afd3 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -15,11 +15,13 @@ int set_memory_ro(unsigned long addr, int numpages);
> int set_memory_rw(unsigned long addr, int numpages);
> int set_memory_x(unsigned long addr, int numpages);
> int set_memory_nx(unsigned long addr, int numpages);
> +void protect_kernel_text_data(void);
> #else
> static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
> static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
> static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
> +static inline void protect_kernel_text_data(void) {};
> #endif
>
> int set_direct_map_invalid_noflush(struct page *page);
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 7d6a04ae3929..b722c5bf892c 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -22,6 +22,7 @@
> #include <asm/cpu_ops.h>
> #include <asm/early_ioremap.h>
> #include <asm/setup.h>
> +#include <asm/set_memory.h>
> #include <asm/sections.h>
> #include <asm/sbi.h>
> #include <asm/tlbflush.h>
> @@ -92,6 +93,7 @@ void __init setup_arch(char **cmdline_p)
> #if IS_ENABLED(CONFIG_RISCV_SBI)
> sbi_init();
> #endif
> + protect_kernel_text_data();
> #ifdef CONFIG_SWIOTLB
> swiotlb_init(1);
> #endif
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index ea933b789a88..5f196f8158d4 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -608,7 +608,7 @@ static inline void setup_vm_final(void)
> #endif /* CONFIG_MMU */
>
> #ifdef CONFIG_STRICT_KERNEL_RWX
> -void mark_rodata_ro(void)
> +void protect_kernel_text_data(void)
> {
> unsigned long text_start = (unsigned long)_text;
> unsigned long text_end = (unsigned long)_etext;
> @@ -617,9 +617,16 @@ void mark_rodata_ro(void)
> unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
>

A comment about that rodata permissions are set later would be nice
here.

> set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> - set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> +}
> +
> +void mark_rodata_ro(void)
> +{
> + unsigned long rodata_start = (unsigned long)__start_rodata;
> + unsigned long data_start = (unsigned long)_data;
> +
> + set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
>
> debug_checkwx();
> }
> --
> 2.25.1
>

--
Sincerely yours,
Mike.