[PATCH v4 3/3] kdump: Protect vmcoreinfo data under the crash memory
Dave Young
dyoung at redhat.com
Wed Apr 26 00:09:36 PDT 2017
On 04/20/17 at 07:39pm, Xunlei Pang wrote:
> Currently vmcoreinfo data is updated at boot time subsys_initcall(),
> it has the risk of being modified by some wrong code during system
> is running.
>
> As a result, vmcore dumped may contain the wrong vmcoreinfo. Later on,
> when using "crash", "makedumpfile", etc utility to parse this vmcore,
> we probably will get "Segmentation fault" or other unexpected errors.
>
> E.g. 1) wrong code overwrites vmcoreinfo_data; 2) further crashes the
> system; 3) trigger kdump, then we obviously will fail to recognize the
> crash context correctly due to the corrupted vmcoreinfo.
>
> Now except for vmcoreinfo, all the crash data is well protected(including
> the cpu note which is fully updated in the crash path, thus its correctness
> is guaranteed). Given that vmcoreinfo data is a large chunk prepared for
> kdump, we better protect it as well.
>
> To solve this, we relocate and copy vmcoreinfo_data to the crash memory
> when kdump is loading via kexec syscalls. Because the whole crash memory
> will be protected by existing arch_kexec_protect_crashkres() mechanism,
> we naturally protect vmcoreinfo_data from write(even read) access under
> kernel direct mapping after kdump is loaded.
>
> Since kdump is usually loaded at the very early stage after boot, we can
> trust the correctness of the vmcoreinfo data copied.
>
> On the other hand, we still need to operate the vmcoreinfo safe copy when
> crash happens to generate vmcoreinfo_note again, we rely on vmap() to map
> out a new kernel virtual address and update to use this new one instead in
> the following crash_save_vmcoreinfo().
>
> BTW, we do not touch vmcoreinfo_note, because it will be fully updated
> using the protected vmcoreinfo_data after crash which is surely correct
> just like the cpu crash note.
>
> Cc: Michael Holzheu <holzheu at linux.vnet.ibm.com>
> Signed-off-by: Xunlei Pang <xlpang at redhat.com>
> ---
> v3->v4:
> -Rebased on the latest linux-next
> -Copy vmcoreinfo after machine_kexec_prepare()
>
> include/linux/crash_core.h | 2 +-
> include/linux/kexec.h | 2 ++
> kernel/crash_core.c | 17 ++++++++++++++++-
> kernel/kexec.c | 8 ++++++++
> kernel/kexec_core.c | 39 +++++++++++++++++++++++++++++++++++++++
> kernel/kexec_file.c | 8 ++++++++
> 6 files changed, 74 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 7d6bc7b..5469adb 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -23,6 +23,7 @@
>
> typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
>
> +void crash_update_vmcoreinfo_safecopy(void *ptr);
> void crash_save_vmcoreinfo(void);
> void arch_crash_save_vmcoreinfo(void);
> __printf(1, 2)
> @@ -54,7 +55,6 @@
> vmcoreinfo_append_str("PHYS_BASE=%lx\n", (unsigned long)value)
>
> extern u32 *vmcoreinfo_note;
> -extern size_t vmcoreinfo_size;
>
> Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
> void *data, size_t data_len);
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index c9481eb..3ea8275 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -181,6 +181,7 @@ struct kimage {
> unsigned long start;
> struct page *control_code_page;
> struct page *swap_page;
> + void *vmcoreinfo_data_copy; /* locates in the crash memory */
>
> unsigned long nr_segments;
> struct kexec_segment segment[KEXEC_SEGMENT_MAX];
> @@ -250,6 +251,7 @@ extern void *kexec_purgatory_get_symbol_addr(struct kimage *image,
> int kexec_should_crash(struct task_struct *);
> int kexec_crash_loaded(void);
> void crash_save_cpu(struct pt_regs *regs, int cpu);
> +extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
>
> extern struct kimage *kexec_image;
> extern struct kimage *kexec_crash_image;
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 43cdb00..a29e9ad 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -15,9 +15,12 @@
>
> /* vmcoreinfo stuff */
> static unsigned char *vmcoreinfo_data;
> -size_t vmcoreinfo_size;
> +static size_t vmcoreinfo_size;
> u32 *vmcoreinfo_note;
>
> +/* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */
May make it clearer like:
/* Trusted vmcoreinfo copy in the kdump reserved memory */
> +static unsigned char *vmcoreinfo_data_safecopy;
> +
> /*
> * parsing the "crashkernel" commandline
> *
> @@ -323,11 +326,23 @@ static void update_vmcoreinfo_note(void)
> final_note(buf);
> }
>
> +void crash_update_vmcoreinfo_safecopy(void *ptr)
> +{
> + if (ptr)
> + memcpy(ptr, vmcoreinfo_data, vmcoreinfo_size);
> +
> + vmcoreinfo_data_safecopy = ptr;
> +}
> +
> void crash_save_vmcoreinfo(void)
> {
> if (!vmcoreinfo_note)
> return;
>
> + /* Use the safe copy to generate vmcoreinfo note if have */
> + if (vmcoreinfo_data_safecopy)
> + vmcoreinfo_data = vmcoreinfo_data_safecopy;
> +
> vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
> update_vmcoreinfo_note();
> }
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 980936a..e62ec4d 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -144,6 +144,14 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
> if (ret)
> goto out;
>
> + /*
> + * Some architecture(like S390) may touch the crash memory before
> + * machine_kexec_prepare(), we must copy vmcoreinfo data after it.
> + */
> + ret = kimage_crash_copy_vmcoreinfo(image);
> + if (ret)
> + goto out;
> +
> for (i = 0; i < nr_segments; i++) {
> ret = kimage_load_segment(image, &image->segment[i]);
> if (ret)
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index ae1a3ba..bac1b4f 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -481,6 +481,40 @@ struct page *kimage_alloc_control_pages(struct kimage *image,
> return pages;
> }
>
> +int kimage_crash_copy_vmcoreinfo(struct kimage *image)
> +{
> + struct page *vmcoreinfo_page;
> + void *safecopy;
> +
> + if (image->type != KEXEC_TYPE_CRASH)
> + return 0;
> +
> + /*
> + * For kdump, allocate one vmcoreinfo safe copy from the
> + * crash memory. as we have arch_kexec_protect_crashkres()
> + * after kexec syscall, we naturally protect it from write
> + * (even read) access under kernel direct mapping. But on
> + * the other hand, we still need to operate it when crash
> + * happens to generate vmcoreinfo note, hereby we rely on
> + * vmap for this purpose.
> + */
> + vmcoreinfo_page = kimage_alloc_control_pages(image, 0);
> + if (!vmcoreinfo_page) {
> + pr_warn("Could not allocate vmcoreinfo buffer\n");
> + return -ENOMEM;
> + }
> + safecopy = vmap(&vmcoreinfo_page, 1, VM_MAP, PAGE_KERNEL);
> + if (!safecopy) {
> + pr_warn("Could not vmap vmcoreinfo buffer\n");
> + return -ENOMEM;
> + }
> +
> + image->vmcoreinfo_data_copy = safecopy;
> + crash_update_vmcoreinfo_safecopy(safecopy);
> +
> + return 0;
> +}
> +
> static int kimage_add_entry(struct kimage *image, kimage_entry_t entry)
> {
> if (*image->entry != 0)
> @@ -598,6 +632,11 @@ void kimage_free(struct kimage *image)
> if (image->file_mode)
> kimage_file_post_load_cleanup(image);
>
> + if (image->vmcoreinfo_data_copy) {
> + crash_update_vmcoreinfo_safecopy(NULL);
> + vunmap(image->vmcoreinfo_data_copy);
> + }
> +
Should move above chunk before the freeing of the actual page?
> kfree(image);
> }
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index b118735..f78f719 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -304,6 +304,14 @@ void kimage_file_post_load_cleanup(struct kimage *image)
> if (ret)
> goto out;
>
> + /*
> + * Some architecture(like S390) may touch the crash memory before
> + * machine_kexec_prepare(), we must copy vmcoreinfo data after it.
> + */
> + ret = kimage_crash_copy_vmcoreinfo(image);
> + if (ret)
> + goto out;
> +
> ret = kexec_calculate_store_digests(image);
> if (ret)
> goto out;
> --
> 1.8.3.1
>
>
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Thanks
Dave
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