On Fri, Apr 09, 2021 at 11:22:51AM -0500, Eric W. Biederman wrote:
>
> During kexec there are two kernel versions at play. The version of
> the running kernel and the version of the kernel that will be booted.
>
> On powerpc it appears people have been using the version of the
> running kernel to attempt to detect properties of the kernel to be
> booted which is just wrong. As the linux kernel version that is being
> detected is a no longer supported kernel just remove that buggy and
> confused code.
>
> On x86_64 the kernel_version is used to compute the starting virtual
> address of the running kernel so a proper core dump may be generated.
> Using the kernel_version stopped working a while ago when the starting
> virtual address became randomized.
>
> The old code was kept for the case where the kernel was not built with
> randomization support, but there is nothing in reading /proc/kcore
> that won't work to detect the starting virtual address even there.
> In fact /proc/kcore must have the starting virtual address or a
> debugger can not make sense of the running kernel.
>
> So just make computing the starting virtual address on x86_64
> unconditional. With a hard coded fallback just in case something went
> wrong.
>
> Doing something with kernel_version() has become important as recent
> stable kernels have seen the minor version to > 255. Just removing
> kernel_version() looks like the best option.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> ---
>
> Can folks please test this patch and verify that it works. I really
> think simply removing the problem code is going to be a much more robust
> solution than papering over the bug.
>
> kexec/Makefile | 1 -
> kexec/arch/i386/crashdump-x86.c | 28 +++++----------
> kexec/arch/ppc/crashdump-powerpc.c | 3 +-
> kexec/arch/ppc64/crashdump-ppc64.c | 3 +-
> kexec/kernel_version.c | 57 ------------------------------
> kexec/kexec.h | 4 ---
> 6 files changed, 11 insertions(+), 85 deletions(-)
> delete mode 100644 kexec/kernel_version.c
>
> diff --git a/kexec/Makefile b/kexec/Makefile
> index 8e3e9ea39664..e69e30950ac8 100644
> --- a/kexec/Makefile
> +++ b/kexec/Makefile
> @@ -22,7 +22,6 @@ KEXEC_SRCS_base += kexec/firmware_memmap.c
> KEXEC_SRCS_base += kexec/crashdump.c
> KEXEC_SRCS_base += kexec/crashdump-xen.c
> KEXEC_SRCS_base += kexec/phys_arch.c
> -KEXEC_SRCS_base += kexec/kernel_version.c
> KEXEC_SRCS_base += kexec/lzma.c
> KEXEC_SRCS_base += kexec/zlib.c
> KEXEC_SRCS_base += kexec/kexec-xen.c
> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> index d5b5b6850fe8..ea3e7c73c621 100644
> --- a/kexec/arch/i386/crashdump-x86.c
> +++ b/kexec/arch/i386/crashdump-x86.c
> @@ -55,16 +55,8 @@ static int get_kernel_page_offset(struct kexec_info *UNUSED(info),
> int kv;
>
> if (elf_info->machine == EM_X86_64) {
> - kv = kernel_version();
> - if (kv < 0)
> - return -1;
> -
> - if (kv < KERNEL_VERSION(2, 6, 27))
> - elf_info->page_offset = X86_64_PAGE_OFFSET_PRE_2_6_27;
> - else if (kv < KERNEL_VERSION(4, 20, 0))
> - elf_info->page_offset = X86_64_PAGE_OFFSET_PRE_4_20_0;
> - else
> - elf_info->page_offset = X86_64_PAGE_OFFSET;
> + /* get_kernel_vaddr_and_size will override this */
> + elf_info->page_offset = X86_64_PAGE_OFFSET;
> }
> else if (elf_info->machine == EM_386) {
> elf_info->page_offset = X86_PAGE_OFFSET;
> @@ -151,17 +143,15 @@ static int get_kernel_vaddr_and_size(struct kexec_info *UNUSED(info),
>
> /* Search for the real PAGE_OFFSET when KASLR memory randomization
> * is enabled */
> - if (get_kernel_sym("page_offset_base") != 0) {
> - for(phdr = ehdr.e_phdr; phdr != end_phdr; phdr++) {
> - if (phdr->p_type == PT_LOAD) {
> - vaddr = phdr->p_vaddr & pud_mask;
> - if (lowest_vaddr == 0 || lowest_vaddr > vaddr)
> - lowest_vaddr = vaddr;
> - }
> + for(phdr = ehdr.e_phdr; phdr != end_phdr; phdr++) {
> + if (phdr->p_type == PT_LOAD) {
> + vaddr = phdr->p_vaddr & pud_mask;
> + if (lowest_vaddr == 0 || lowest_vaddr > vaddr)
> + lowest_vaddr = vaddr;
> }
> - if (lowest_vaddr != 0)
> - elf_info->page_offset = lowest_vaddr;
> }
> + if (lowest_vaddr != 0)
> + elf_info->page_offset = lowest_vaddr;
>
> /* Traverse through the Elf headers and find the region where
> * _stext symbol is located in. That's where kernel is mapped */
> diff --git a/kexec/arch/ppc/crashdump-powerpc.c b/kexec/arch/ppc/crashdump-powerpc.c
> index 4ad026f38dd0..15e85313ff75 100644
> --- a/kexec/arch/ppc/crashdump-powerpc.c
> +++ b/kexec/arch/ppc/crashdump-powerpc.c
> @@ -255,8 +255,7 @@ static void add_cmdline(char *cmdline, char *str)
> int cmdline_size;
> int cmdlen = strlen(cmdline) + strlen(str);
>
> - cmdline_size = (kernel_version() < KERNEL_VERSION(3, 15, 0) ?
> - 512 : COMMAND_LINE_SIZE);
> + cmdline_size = COMMAND_LINE_SIZE;
> if (cmdlen > (cmdline_size - 1))
> die("Command line overflow\n");
> strcat(cmdline, str);
> diff --git a/kexec/arch/ppc64/crashdump-ppc64.c b/kexec/arch/ppc64/crashdump-ppc64.c
> index 26f9a01a8174..addd769de401 100644
> --- a/kexec/arch/ppc64/crashdump-ppc64.c
> +++ b/kexec/arch/ppc64/crashdump-ppc64.c
> @@ -478,8 +478,7 @@ static int add_cmdline_param(char *cmdline, uint64_t addr, char *cmdstr,
> strcat(str, byte);
> len = strlen(str);
> cmdlen = strlen(cmdline) + len;
> - cmdline_size = (kernel_version() < KERNEL_VERSION(3, 15, 0) ?
> - 512 : COMMAND_LINE_SIZE);
> + cmdline_size = COMMAND_LINE_SIZE;
> if (cmdlen > (cmdline_size - 1))
> die("Command line overflow\n");
> strcat(cmdline, str);
> diff --git a/kexec/kernel_version.c b/kexec/kernel_version.c
> deleted file mode 100644
> index 21fb13adf095..000000000000
> --- a/kexec/kernel_version.c
> +++ /dev/null
> @@ -1,57 +0,0 @@
> -#include "kexec.h"
> -#include <errno.h>
> -#include <string.h>
> -#include <sys/utsname.h>
> -#include <string.h>
> -#include <limits.h>
> -#include <stdlib.h>
> -
> -long kernel_version(void)
> -{
> - struct utsname utsname;
> - unsigned long major, minor, patch;
> - char *p;
> -
> - if (uname(&utsname) < 0) {
> - fprintf(stderr, "uname failed: %s\n", strerror(errno));
> - return -1;
> - }
> -
> - p = utsname.release;
> - major = strtoul(p, &p, 10);
> - if (major == ULONG_MAX) {
> - fprintf(stderr, "strtoul failed: %s\n", strerror(errno));
> - return -1;
> - }
> -
> - if (*p++ != '.') {
> - fprintf(stderr, "Unsupported utsname.release: %s\n",
> - utsname.release);
> - return -1;
> - }
> -
> - minor = strtoul(p, &p, 10);
> - if (minor == ULONG_MAX) {
> - fprintf(stderr, "strtoul failed: %s\n", strerror(errno));
> - return -1;
> - }
> -
> - /* There may or may not be a patch level for this kernel */
> - if (*p++ == '.') {
> - patch = strtoul(p, &p, 10);
> - if (patch == ULONG_MAX) {
> - fprintf(stderr, "strtoul failed: %s\n",strerror(errno));
> - return -1;
> - }
> - } else {
> - patch = 0;
> - }
> -
> - if (major >= 256 || minor >= 256 || patch >= 256) {
> - fprintf(stderr, "Unsupported utsname.release: %s\n",
> - utsname.release);
> - return -1;
> - }
> -
> - return KERNEL_VERSION(major, minor, patch);
> -}
> diff --git a/kexec/kexec.h b/kexec/kexec.h
> index f0f347d5e9e0..595dd681db6d 100644
> --- a/kexec/kexec.h
> +++ b/kexec/kexec.h
> @@ -179,10 +179,6 @@ struct arch_map_entry {
> extern const struct arch_map_entry arches[];
> long physical_arch(void);
>
> -#define KERNEL_VERSION(major, minor, patch) \
> - (((major) << 16) | ((minor) << 8) | patch)
> -long kernel_version(void);
> -
> void usage(void);
> int get_memory_ranges(struct memory_range **range, int *ranges,
> unsigned long kexec_flags);
> --
> 2.30.1
[ Sorry this has taken so long --jak ]
Successful dump was acquired using a hand-built 4.4.262-kdump kernel.
The new kdump tools were installed in /usr/local, and a modified kdumpctl
(making it use the new tools) was put in in /tmp/kdumpctl. When I do:
kdumpctl start
echo c >/proc/sysrq
I get the 'Unsupported utsname.release' error message, and the 'echo c'
fails to create a dump directory in /var/crash. When I do:
/tmp/kdumpctl start
echo c >/proc/sysrq
I no longer get the 'Unsupported' error message and a dump directory
appears in /var/crash. I did not test if the dump itself was good.
Tested-by: Joe Korty <joe.korty@xxxxxxxxxxxxxxxx>
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