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

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Date:   Tue, 26 Feb 2019 11:11:53 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Chao Fan <fanc.fnst@...fujitsu.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>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/boot/KASLR: skip the specified crashkernel reserved region

On Mon, Feb 25, 2019 at 4:23 PM Chao Fan <fanc.fnst@...fujitsu.com> wrote:
>
> 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.
>
Yes, it is better.
> >+
> >+      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.
>
OK.
> >+}
> >
> > 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();
>
Yes, it is outdated, should fix the comment.
> > {
> >@@ -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*().
>
It follows the name of parse_crashkernel_simple()

Thanks,
Pingfan