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SubjectRe: [PATCH v16 16/16] arm64: kexec_file: add kaslr support
On Thu, Nov 15, 2018 at 02:52:55PM +0900, AKASHI Takahiro wrote:
> Adding "kaslr-seed" to dtb enables triggering kaslr, or kernel virtual
> address randomization, at secondary kernel boot. We always do this as
> it will have no harm on kaslr-incapable kernel.
>
> We don't have any "switch" to turn off this feature directly, but still
> can suppress it by passing "nokaslr" as a kernel boot argument.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
> arch/arm64/kernel/machine_kexec_file.c | 46 +++++++++++++++++++++++++-
> 1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index ab296b98d633..a0a730bd9be6 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -16,6 +16,7 @@
> #include <linux/libfdt.h>
> #include <linux/memblock.h>
> #include <linux/of_fdt.h>
> +#include <linux/random.h>
> #include <linux/slab.h>
> #include <linux/string.h>
> #include <linux/types.h>
> @@ -28,6 +29,7 @@
> #define FDT_PSTR_INITRD_STA "linux,initrd-start"
> #define FDT_PSTR_INITRD_END "linux,initrd-end"
> #define FDT_PSTR_BOOTARGS "bootargs"
> +#define FDT_PSTR_KASLR_SEED "kaslr-seed"
>
> const struct kexec_file_ops * const kexec_file_loaders[] = {
> &kexec_image_ops,
> @@ -46,11 +48,38 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
> return kexec_image_post_load_cleanup_default(image);
> }
>
> +/* crng needs to have been initialized for providing kaslr-seed */
> +static int random_ready;
> +
> +static void random_ready_notified(struct random_ready_callback *unused)
> +{
> + random_ready = 1;
> +}
> +
> +static struct random_ready_callback random_ready_cb = {
> + .func = random_ready_notified,
> +};
> +
> +static __init int init_random_ready_cb(void)
> +{
> + int ret;
> +
> + ret = add_random_ready_callback(&random_ready_cb);
> + if (ret == -EALREADY)
> + random_ready = 1;
> + else if (ret)
> + pr_warn("failed to add a callback for random_ready\n");
> +
> + return 0;
> +}
> +late_initcall(init_random_ready_cb)

Why can't we just call crng_ready()?

> +
> static int setup_dtb(struct kimage *image,
> unsigned long initrd_load_addr, unsigned long initrd_len,
> char *cmdline, void *dtb)
> {
> int nodeoffset;
> + u64 value;
> int ret;
>
> nodeoffset = fdt_path_offset(dtb, "/chosen");
> @@ -106,12 +135,27 @@ static int setup_dtb(struct kimage *image,
> return -EINVAL;
> }
>
> + /* add kaslr-seed */
> + ret = fdt_delprop(dtb, nodeoffset, FDT_PSTR_KASLR_SEED);
> + if (ret && (ret != -FDT_ERR_NOTFOUND))
> + return -EINVAL;
> +
> + if (random_ready) {
> + get_random_bytes(&value, sizeof(value));

get_random_u64() ?

> + ret = fdt_setprop_u64(dtb, nodeoffset, FDT_PSTR_KASLR_SEED,
> + value);
> + if (ret)
> + return (ret == -FDT_ERR_NOSPACE ? -ENOMEM : -EINVAL);
> + } else {

Wouldn't we be better off preserving the previous seed here, if it was
present?

> + pr_notice("kaslr-seed won't be fed\n");

"fed" is probably not the right word here.

Will

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