linux-kernel - Re: [PATCHv2] x86/boot/KASLR: skip the specified crashkernel reserved region

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Date:   Wed, 20 Mar 2019 08:25:24 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Will Deacon <will.deacon@....com>,
        Nicolas Pitre <nico@...aro.org>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] x86/boot/KASLR: skip the specified crashkernel
 reserved region

Please change subject as:

"x86/boot/KASLR: skip the specified crashkernel region"

Don't see why reserved is needed here.

On 03/13/19 at 12:19pm, Pingfan Liu wrote:
> crashkernel=x@y option may fail to reserve the required memory region if
> KASLR puts kernel into the region. To avoid this uncertainty, making KASLR
> skip the required region.
> 
> Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Nicolas Pitre <nico@...aro.org>
> Cc: Pingfan Liu <kernelfans@...il.com>
> Cc: Chao Fan <fanc.fnst@...fujitsu.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: linux-kernel@...r.kernel.org
> ---
> v1 -> v2: fix some trival format
> 
>  arch/x86/boot/compressed/kaslr.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 9ed9709..e185318 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -109,6 +109,7 @@ enum mem_avoid_index {
>  	MEM_AVOID_BOOTPARAMS,
>  	MEM_AVOID_MEMMAP_BEGIN,
>  	MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
> +	MEM_AVOID_CRASHKERNEL,
>  	MEM_AVOID_MAX,
>  };
>  
> @@ -240,6 +241,25 @@ static void parse_gb_huge_pages(char *param, char *val)
>  	}
>  }
>  
> +/* parse crashkernel=x@y option */
> +static void mem_avoid_crashkernel_simple(char *option)

Chao ever mentioned this, I want to ask again, why does it has to be
xxx_simple()?

Except of these, patch looks good to me. It's a nice catch, and only
need a simple fix based on the current code.

Thanks
Baoquan

> +{
> +	unsigned long long crash_size, crash_base;
> +	char *cur = option;
> +
> +	crash_size = memparse(option, &cur);
> +	if (option == cur)
> +		return;
> +
> +	if (*cur == '@') {
> +		option = cur + 1;
> +		crash_base = memparse(option, &cur);
> +		if (option == cur)
> +			return;
> +		mem_avoid[MEM_AVOID_CRASHKERNEL].start = crash_base;
> +		mem_avoid[MEM_AVOID_CRASHKERNEL].size = crash_size;
> +	}
> +}
>  
>  static void handle_mem_options(void)
>  {
> @@ -250,7 +270,7 @@ static void handle_mem_options(void)
>  	u64 mem_size;
>  
>  	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
> -		!strstr(args, "hugepages"))
> +		!strstr(args, "hugepages") && !strstr(args, "crashkernel="))
>  		return;
>  
>  	tmp_cmdline = malloc(len + 1);
> @@ -286,6 +306,8 @@ static void handle_mem_options(void)
>  				goto out;
>  
>  			mem_limit = mem_size;
> +		} else if (strstr(param, "crashkernel")) {
> +			mem_avoid_crashkernel_simple(val);
>  		}
>  	}
>  
> @@ -414,7 +436,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>  
>  	/* We don't need to set a mapping for setup_data. */
>  
> -	/* Mark the memmap regions we need to avoid */
> +	/* Mark the regions we need to avoid */
>  	handle_mem_options();
>  
>  #ifdef CONFIG_X86_VERBOSE_BOOTUP
> -- 
> 2.7.4
>