Re: [PATCH] kexec: Export memory sections virtual addresses to vmcoreinfo

Eric W. Biederman
2016-10-06T20:10:01Z

Baoquan He <bhe@redhat.com> writes:

> KASLR memory randomization can randomize the base of the physical memory
> mapping (PAGE_OFFSET), vmalloc (VMALLOC_START) and vmemmap
> (VMEMMAP_START). These need be exported to VMCOREINFO so that user space
> utility, mainly makedumpfile can use them to identify the base of each
> memory section. Here using VMCOREINFO_NUMBER we can reuse the existing
> struct number_table in makedumpfile to import data easily.
>
> Since they are related to x86_64 only, put them into
> arch_crash_save_vmcoreinfo. And move the exportion of KERNEL_IMAGE_SIZE
> together since it's also for x86_64 only.

*Scratches my head* I would have thought this information would have
better fit in the ELF header. Where it actually has a field for virtual
address. It also has a field for physical address, and a third field
for offset in the file (which is where the kdump finds these things in
memory aftewards).

Why do we need need more magic vmcoreinfo to handle this?

Eric

>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> arch/x86/kernel/machine_kexec_64.c | 4 ++++
> kernel/kexec_core.c | 3 ---
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 5a294e4..e150dd7 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -337,6 +337,10 @@ void arch_crash_save_vmcoreinfo(void)
> #endif
> vmcoreinfo_append_str("KERNELOFFSET=%lx\n",
> kaslr_offset());
> + VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
> + VMCOREINFO_NUMBER(PAGE_OFFSET);
> + VMCOREINFO_NUMBER(VMALLOC_START);
> + VMCOREINFO_NUMBER(VMEMMAP_START);
> }
>
> /* arch-dependent functionality related to kexec file-based syscall */
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 5616755..8ad3a29e 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1467,9 +1467,6 @@ static int __init crash_save_vmcoreinfo_init(void)
> #endif
> VMCOREINFO_NUMBER(PG_head_mask);
> VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
> -#ifdef CONFIG_X86
> - VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
> -#endif
> #ifdef CONFIG_HUGETLB_PAGE
> VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
> #endif