[PATCH] arm64: Add support to supply 'kaslr-seed' to secondary kernel
AKASHI Takahiro
takahiro.akashi at linaro.org
Sun Apr 15 19:30:16 PDT 2018
Bhupesh,
On Sun, Apr 15, 2018 at 01:49:40AM +0530, Bhupesh Sharma wrote:
> This patch adds the support to supply 'kaslr-seed' to secondary kernel,
> when we do a 'kexec warm reboot to another kernel' (although the
> behaviour remains the same for the 'kdump' case as well) on arm64
> platforms using the 'kexec_load' invocation method.
>
> Lets consider the case where the primary kernel working on the arm64
> platform supports kaslr (i.e 'CONFIG_RANDOMIZE_BASE' was set to y and
> we have a compliant EFI firmware which supports EFI_RNG_PROTOCOL and
> hence can pass a non-zero (valid) seed to the primary kernel).
>
> Now the primary kernel reads the 'kaslr-seed' and wipes it to 0 and
> uses the seed value to randomize for e.g. the module base address
> offset.
>
> In the case of 'kexec_load' (or even kdump for brevity),
> we rely on the user-space kexec-tools to pass an appropriate dtb to the
> secondary kernel and since 'kaslr-seed' is wiped to 0 by the primary
> kernel, the secondary will essentially work with *nokaslr* as
> 'kaslr-seed' is set to 0 when it is passed to the secondary kernel.
>
> This can be true even in case the secondary kernel had
> 'CONFIG_RANDOMIZE_BASE' and 'CONFIG_RANDOMIZE_MODULE_REGION_FULL' set to
> y.
>
> This patch addresses this issue by first checking if the device tree
> provided by the firmware to the kernel supports the 'kaslr-seed'
> property and verifies that it is really wiped to 0. If this condition is
> met, it fixes up the 'kaslr-seed' property by using the getrandom()
> syscall to get a suitable random number.
>
> I verified this patch on my Qualcomm arm64 board and here are some test
> results:
>
> 1. Ensure that the primary kernel is boot'ed with 'kaslr-seed'
> dts property and it is really wiped to 0:
>
> [root at qualcomm-amberwing]# dtc -I dtb -O dts /sys/firmware/fdt | grep -A 10 -i chosen
> chosen {
> kaslr-seed = <0x0 0x0>;
> ...
> }
>
> 2. Now issue 'kexec_load' to load the secondary kernel (let's assume
> that we are using the same kernel as the secondary kernel):
> # kexec -l /boot/vmlinuz-`uname -r` --initrd=/boot/initramfs-`uname
> -r`.img --reuse-cmdline -d
>
> 3. Issue 'kexec -e' to warm boot to the secondary:
> # kexec -e
>
> 4. Now after the secondary boots, confirm that the load address of the
> modules is randomized in every successive boot:
>
> [root at qualcomm-amberwing]# cat /proc/modules
> sunrpc 524288 1 - Live 0xffff0307db190000
> vfat 262144 1 - Live 0xffff0307db110000
> fat 262144 1 vfat, Live 0xffff0307db090000
> crc32_ce 262144 0 - Live 0xffff0307d8c70000
> ...
>
> Signed-off-by: Bhupesh Sharma <bhsharma at redhat.com>
> ---
> kexec/arch/arm64/kexec-arm64.c | 135 +++++++++++++++++++++++++++++------------
> 1 file changed, 97 insertions(+), 38 deletions(-)
>
> diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
> index 62f37585b788..2ab11227447a 100644
> --- a/kexec/arch/arm64/kexec-arm64.c
> +++ b/kexec/arch/arm64/kexec-arm64.c
> @@ -15,6 +15,11 @@
> #include <linux/elf-em.h>
> #include <elf.h>
>
> +#include <unistd.h>
> +#include <syscall.h>
> +#include <errno.h>
> +#include <linux/random.h>
> +
> #include "kexec.h"
> #include "kexec-arm64.h"
> #include "crashdump.h"
> @@ -392,11 +397,13 @@ static int fdt_setprop_range(void *fdt, int nodeoffset,
> static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
> {
> uint32_t address_cells, size_cells;
> - int range_len;
> - int nodeoffset;
> + uint64_t fdt_val64;
> + uint64_t *prop;
> char *new_buf = NULL;
> + int len, range_len;
> + int nodeoffset;
> int new_size;
> - int result;
> + int result, kaslr_seed;
>
> result = fdt_check_header(dtb->buf);
>
> @@ -407,47 +414,99 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
>
> result = set_bootargs(dtb, command_line);
>
> - if (on_crash) {
> - /* determine #address-cells and #size-cells */
> - result = get_cells_size(dtb->buf, &address_cells, &size_cells);
> - if (result) {
> - fprintf(stderr,
> - "kexec: cannot determine cells-size.\n");
> - result = -EINVAL;
> - goto on_error;
> - }
> + /* determine #address-cells and #size-cells */
> + result = get_cells_size(dtb->buf, &address_cells, &size_cells);
> + if (result) {
> + fprintf(stderr, "kexec: cannot determine cells-size.\n");
> + result = -EINVAL;
> + goto on_error;
> + }
>
> - if (!cells_size_fitted(address_cells, size_cells,
> - &elfcorehdr_mem)) {
> - fprintf(stderr,
> - "kexec: elfcorehdr doesn't fit cells-size.\n");
> + if (!cells_size_fitted(address_cells, size_cells,
> + &elfcorehdr_mem)) {
> + fprintf(stderr, "kexec: elfcorehdr doesn't fit cells-size.\n");
> + result = -EINVAL;
> + goto on_error;
> + }
> +
> + if (!cells_size_fitted(address_cells, size_cells,
> + &crash_reserved_mem)) {
> + fprintf(stderr, "kexec: usable memory range doesn't fit cells-size.\n");
> + result = -EINVAL;
> + goto on_error;
> + }
> +
> + /* duplicate dt blob */
> + range_len = sizeof(uint32_t) * (address_cells + size_cells);
> + new_size = fdt_totalsize(dtb->buf)
> + + fdt_prop_len(PROP_ELFCOREHDR, range_len)
> + + fdt_prop_len(PROP_USABLE_MEM_RANGE, range_len);
> +
> + new_buf = xmalloc(new_size);
> + result = fdt_open_into(dtb->buf, new_buf, new_size);
> + if (result) {
> + dbgprintf("%s: fdt_open_into failed: %s\n", __func__,
> + fdt_strerror(result));
> + result = -ENOSPC;
> + goto on_error;
> + }
> +
> + /* fixup 'kaslr-seed' with a random value, if supported */
> + nodeoffset = fdt_path_offset(new_buf, "/chosen");
> + prop = fdt_getprop_w(new_buf, nodeoffset,
> + "kaslr-seed", &len);
> + if (!prop || len != sizeof(uint64_t)) {
Do we need this check?
Please note that people are allowed to provide a dtb explicitly
at command line and may want to use kexec as bootloader on
no-uefi platform.
> + dbgprintf("%s: no kaslr-seed found: %s\n",
> + __func__, fdt_strerror(result));
> + /* for kexec warm reboot case, we don't need to fixup
> + * other dtb properties
> + */
> + if (!on_crash)
> + goto free_new_buf;
> +
> + } else {
> + kaslr_seed = fdt64_to_cpu(*prop);
> +
> + /* kaslr_seed must be wiped clean by primary
> + * kernel during boot
> + */
> + if (kaslr_seed != 0) {
> + dbgprintf("%s: kaslr-seed is not wiped to 0.\n",
> + __func__);
Ditto
If this is a user-provided dtb, there is no reason to reject it.
I think all what is needed here is to feed a *sane* dtb to kexec.
So along with the comment above, it may be useful to add a command line
option for turning on or off "kaslr-seed".
> result = -EINVAL;
> goto on_error;
> }
>
> - if (!cells_size_fitted(address_cells, size_cells,
> - &crash_reserved_mem)) {
> - fprintf(stderr,
> - "kexec: usable memory range doesn't fit cells-size.\n");
> + /*
> + * Invoke the getrandom system call with
> + * GRND_NONBLOCK, to make sure we
> + * have a valid random seed to pass to the
> + * secondary kernel.
> + */
> + result = syscall(SYS_getrandom, &fdt_val64,
> + sizeof(fdt_val64),
> + GRND_NONBLOCK);
Why do you use syscall() here?
> +
> + if(result == -1) {
> + dbgprintf("%s: Reading random bytes failed.\n",
> + __func__);
> result = -EINVAL;
> goto on_error;
> }
>
> - /* duplicate dt blob */
> - range_len = sizeof(uint32_t) * (address_cells + size_cells);
> - new_size = fdt_totalsize(dtb->buf)
> - + fdt_prop_len(PROP_ELFCOREHDR, range_len)
> - + fdt_prop_len(PROP_USABLE_MEM_RANGE, range_len);
> -
> - new_buf = xmalloc(new_size);
> - result = fdt_open_into(dtb->buf, new_buf, new_size);
> + nodeoffset = fdt_path_offset(new_buf, "/chosen");
> + result = fdt_setprop_inplace(new_buf,
> + nodeoffset, "kaslr-seed",
> + &fdt_val64, sizeof(fdt_val64));
> if (result) {
> - dbgprintf("%s: fdt_open_into failed: %s\n", __func__,
> - fdt_strerror(result));
> - result = -ENOSPC;
> + dbgprintf("%s: fdt_setprop failed: %s\n",
> + __func__, fdt_strerror(result));
> + result = -EINVAL;
> goto on_error;
> }
> + }
>
> + if (on_crash) {
> /* add linux,elfcorehdr */
> nodeoffset = fdt_path_offset(new_buf, "/chosen");
> result = fdt_setprop_range(new_buf, nodeoffset,
> @@ -455,7 +514,7 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
> address_cells, size_cells);
> if (result) {
> dbgprintf("%s: fdt_setprop failed: %s\n", __func__,
> - fdt_strerror(result));
> + fdt_strerror(result));
> result = -EINVAL;
> goto on_error;
> }
> @@ -467,23 +526,23 @@ static int setup_2nd_dtb(struct dtb *dtb, char *command_line, int on_crash)
> address_cells, size_cells);
> if (result) {
> dbgprintf("%s: fdt_setprop failed: %s\n", __func__,
> - fdt_strerror(result));
> + fdt_strerror(result));
> result = -EINVAL;
> goto on_error;
> }
> -
> - fdt_pack(new_buf);
> - dtb->buf = new_buf;
> - dtb->size = fdt_totalsize(new_buf);
> }
>
> - dump_reservemap(dtb);
> + fdt_pack(new_buf);
> + dtb->buf = new_buf;
> + dtb->size = fdt_totalsize(new_buf);
>
> + dump_reservemap(dtb);
>
> return result;
>
> on_error:
> fprintf(stderr, "kexec: %s failed.\n", __func__);
> +free_new_buf:
Well, technically correct, but it looks odd as it is placed
on *error* return path.
You also miss dump_reservemap().
Thanks,
-Takahiro AKASHI
> if (new_buf)
> free(new_buf);
>
> --
> 2.7.4
>
More information about the kexec
mailing list