[PATCH] arm64:mm Remove the redundant initrd memblock codes

[Ard Biesheuvel]

> On 4 jul. 2016, at 06:53, Dennis Chen <dennis.chen at arm.com> wrote:
> 
> The memory range between initrd_start and initrd_end was added to the memblock
> twice unnecessarily in the same function before initrd memory range can be freed.
> This patch merge those codes into one piece of block and add the initrd memory
> range only once, also it makes the code clean and simple.
> 

This is likely to break under KASLR (and I would recommend that you test with kaslr enabled when you propose changes to this code)

The randomization of memstart_addr needs to execute /after/ adding back the initrd, otherwise the chosen value of memstart_addr may push the initrd beyond the end of the linear area into the userland range.


> Signed-off-by: Dennis Chen <dennis.chen at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Steve Capper <steve.capper at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Cc: Will Deacon <will.deacon at arm.com>
> ---
> arch/arm64/mm/init.c | 58 +++++++++++++++++++++++-----------------------------
> 1 file changed, 26 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 2ade7a6..cf26cdb 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -228,6 +228,29 @@ void __init arm64_memblock_init(void)
>        memblock_add(__pa(_text), (u64)(_end - _text));
>    }
> 
> +    if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> +        extern u16 memstart_offset_seed;
> +        u64 range = linear_region_size -
> +                (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> +
> +        /*
> +         * If the size of the linear region exceeds, by a sufficient
> +         * margin, the size of the region that the available physical
> +         * memory spans, randomize the linear region as well.
> +         */
> +        if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> +            range = range / ARM64_MEMSTART_ALIGN + 1;
> +            memstart_addr -= ARM64_MEMSTART_ALIGN *
> +                     ((range * memstart_offset_seed) >> 16);
> +        }
> +    }
> +
> +    /*
> +     * Register the kernel text, kernel data, initrd, and initial
> +     * pagetables with memblock.
> +     */
> +    memblock_reserve(__pa(_text), _end - _text);
> +
>    if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
>        /*
>         * Add back the memory we just removed if it results in the
> @@ -254,41 +277,12 @@ void __init arm64_memblock_init(void)
>            memblock_remove(base, size); /* clear MEMBLOCK_ flags */
>            memblock_add(base, size);
>            memblock_reserve(base, size);
> +            /* the generic initrd code expects virtual addresses */
> +            initrd_start = __phys_to_virt(initrd_start);
> +            initrd_end = __phys_to_virt(initrd_end);
>        }
>    }
> 
> -    if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> -        extern u16 memstart_offset_seed;
> -        u64 range = linear_region_size -
> -                (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> -
> -        /*
> -         * If the size of the linear region exceeds, by a sufficient
> -         * margin, the size of the region that the available physical
> -         * memory spans, randomize the linear region as well.
> -         */
> -        if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> -            range = range / ARM64_MEMSTART_ALIGN + 1;
> -            memstart_addr -= ARM64_MEMSTART_ALIGN *
> -                     ((range * memstart_offset_seed) >> 16);
> -        }
> -    }
> -
> -    /*
> -     * Register the kernel text, kernel data, initrd, and initial
> -     * pagetables with memblock.
> -     */
> -    memblock_reserve(__pa(_text), _end - _text);
> -#ifdef CONFIG_BLK_DEV_INITRD
> -    if (initrd_start) {
> -        memblock_reserve(initrd_start, initrd_end - initrd_start);
> -
> -        /* the generic initrd code expects virtual addresses */
> -        initrd_start = __phys_to_virt(initrd_start);
> -        initrd_end = __phys_to_virt(initrd_end);
> -    }
> -#endif
> -
>    early_init_fdt_scan_reserved_mem();
> 
>    /* 4GB maximum for 32-bit only capable devices */
> -- 
> 1.8.3.1
>