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

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Date:   Mon, 25 Feb 2019 16:23:18 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.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>, Baoquan He <bhe@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Nicolas Pitre <nico@...aro.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/boot/KASLR: skip the specified crashkernel reserved
 region

On Mon, Feb 25, 2019 at 03:59:56PM +0800, 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
>---
> arch/x86/boot/compressed/kaslr.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>

Hi Pingfan,

Some not important comments:

>diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>index 9ed9709..728bc4b 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 +241,27 @@ static void parse_gb_huge_pages(char *param, char *val)
> 	}
> }
> 
>+/* parse crashkernel=x@y option */
>+static int mem_avoid_crashkernel_simple(char *option)
>+{
>+	char *cur = option;
>+	unsigned long long crash_size, crash_base;

Change the position of two lines above.

>+
>+	crash_size = memparse(option, &cur);
>+	if (option == cur)
>+		return -EINVAL;
>+
>+	if (*cur == '@') {
>+		option = cur + 1;
>+		crash_base = memparse(option, &cur);
>+		if (option == cur)
>+			return -EINVAL;
>+		mem_avoid[MEM_AVOID_CRASHKERNEL].start = crash_base;
>+		mem_avoid[MEM_AVOID_CRASHKERNEL].size = crash_size;
>+	}
>+
>+	return 0;

You just call this function and don't use its return value.
So why not change it as void type.

>+}
> 
> static void handle_mem_options(void)

If you want to change this function, I think you could change the
function name and the comment:

        /* Mark the memmap regions we need to avoid */
        handle_mem_options();

> {
>@@ -250,7 +272,7 @@ 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 +308,8 @@ static void handle_mem_options(void)
> 				goto out;
> 
> 			mem_limit = mem_size;
>+		} else if (strstr(param, "crashkernel")) {
>+			mem_avoid_crashkernel_simple(val);

I am wondering why you call this function mem_avoid_crashkernel_*simple*().

Thanks,
Chao Fan

> 		}
> 	}
> 
>-- 
>2.7.4
>
>
>