On Tue, Jan 5, 2021 at 1:31 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> The kernel is now mapped at the end of the address space and it should
> be accessed through this mapping only: so map the whole kernel in the
> linear mapping as read only.
>
> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> ---
> arch/riscv/include/asm/page.h | 9 ++++++++-
> arch/riscv/mm/init.c | 29 +++++++++++++++++++++--------
> 2 files changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 98188e315e8d..a93e35aaa717 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -102,8 +102,15 @@ extern unsigned long pfn_base;
> extern unsigned long max_low_pfn;
> extern unsigned long min_low_pfn;
> extern unsigned long kernel_virt_addr;
> +extern uintptr_t load_pa, load_sz;
> +
> +#define linear_mapping_pa_to_va(x) ((void *)((unsigned long)(x) + va_pa_offset))
> +#define kernel_mapping_pa_to_va(x) \
> + ((void *)((unsigned long) (x) + va_kernel_pa_offset))
> +#define __pa_to_va_nodebug(x) \
> + ((x >= load_pa && x < load_pa + load_sz) ? \
> + kernel_mapping_pa_to_va(x): linear_mapping_pa_to_va(x))
This change should be part of PATCH1
>
> -#define __pa_to_va_nodebug(x) ((void *)((unsigned long) (x) + va_pa_offset))
> #define linear_mapping_va_to_pa(x) ((unsigned long)(x) - va_pa_offset)
> #define kernel_mapping_va_to_pa(x) \
> ((unsigned long)(x) - va_kernel_pa_offset)
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9d06ff0e015a..7b87c14f1d24 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -159,8 +159,6 @@ void __init setup_bootmem(void)
> {
> phys_addr_t mem_start = 0;
> phys_addr_t start, end = 0;
> - phys_addr_t vmlinux_end = __pa_symbol(&_end);
> - phys_addr_t vmlinux_start = __pa_symbol(&_start);
This as well.
> u64 i;
>
> /* Find the memory region containing the kernel */
> @@ -168,7 +166,7 @@ void __init setup_bootmem(void)
> phys_addr_t size = end - start;
> if (!mem_start)
> mem_start = start;
> - if (start <= vmlinux_start && vmlinux_end <= end)
> + if (start <= load_pa && (load_pa + load_sz) <= end)
> BUG_ON(size == 0);
> }
>
> @@ -179,8 +177,13 @@ void __init setup_bootmem(void)
> */
> memblock_enforce_memory_limit(mem_start - PAGE_OFFSET);
>
> - /* Reserve from the start of the kernel to the end of the kernel */
> - memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
> + /*
> + * Reserve from the start of the kernel to the end of the kernel
> + * and make sure we align the reservation on PMD_SIZE since we will
> + * map the kernel in the linear mapping as read-only: we do not want
> + * any allocation to happen between _end and the next pmd aligned page.
> + */
> + memblock_reserve(load_pa, (load_sz + PMD_SIZE - 1) & ~(PMD_SIZE - 1));
>
> max_pfn = PFN_DOWN(memblock_end_of_DRAM());
> max_low_pfn = max_pfn;
> @@ -438,7 +441,9 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
> #endif
>
> -static uintptr_t load_pa, load_sz;
> +uintptr_t load_pa, load_sz;
> +EXPORT_SYMBOL(load_pa);
> +EXPORT_SYMBOL(load_sz);
I think all changes till here should be in PATCH1.
Only the changes here onwards seems to be as-per PATCH description.
>
> static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> {
> @@ -596,9 +601,17 @@ static void __init setup_vm_final(void)
>
> map_size = best_map_size(start, end - start);
> for (pa = start; pa < end; pa += map_size) {
> - va = (uintptr_t)__va(pa);
> + pgprot_t prot = PAGE_KERNEL;
> +
> + /* Protect the kernel mapping that lies in the linear mapping */
> + if (pa >= __pa(_start) && pa < __pa(_end))
> + prot = PAGE_KERNEL_READ;
> +
> + /* Make sure we get virtual addresses in the linear mapping */
> + va = (uintptr_t)linear_mapping_pa_to_va(pa);
> +
> create_pgd_mapping(swapper_pg_dir, va, pa,
> - map_size, PAGE_KERNEL);
> + map_size, prot);
> }
> }
>
> --
> 2.20.1
>
Regards,
Anup
