Re: [PATCH v4 18/21] arm64: Move "nokaslr" over to the early cpufeature infrastructure

David Brazdil
2021-01-18T14:49:46Z

On Mon, Jan 18, 2021 at 09:45:30AM +0000, Marc Zyngier wrote:
> Given that the early cpufeature infrastructure has borrowed quite
> a lot of code from the kaslr implementation, let's reimplement
> the matching of the "nokaslr" option with it.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: David Brazdil <dbrazdil@google.com>

> ---
> arch/arm64/kernel/idreg-override.c | 17 ++++++++++++++
> arch/arm64/kernel/kaslr.c | 37 +++---------------------------
> 2 files changed, 20 insertions(+), 34 deletions(-)
>
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index 1db54878b2c4..143fe7b8e3ce 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -33,8 +33,24 @@ static const struct reg_desc mmfr1 __initdata = {
> },
> };
>
> +extern u64 kaslr_feature_val;
> +extern u64 kaslr_feature_mask;
> +
> +static const struct reg_desc kaslr __initdata = {
> + .name = "kaslr",
> +#ifdef CONFIG_RANDOMIZE_BASE
> + .val = &kaslr_feature_val,
> + .mask = &kaslr_feature_mask,
> +#endif
> + .fields = {
> + { "disabled", 0 },
> + {}
> + },
> +};
> +
> static const struct reg_desc * const regs[] __initdata = {
> &mmfr1,
> + &kaslr,
> };
>
> static const struct {
> @@ -43,6 +59,7 @@ static const struct {
> } aliases[] __initdata = {
> { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
> { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
> + { "nokaslr", "kaslr.disabled=1" },
> };
>
> static int __init find_field(const char *cmdline, const struct reg_desc *reg,
> diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
> index 5fc86e7d01a1..dcc4a5aadbe2 100644
> --- a/arch/arm64/kernel/kaslr.c
> +++ b/arch/arm64/kernel/kaslr.c
> @@ -51,39 +51,8 @@ static __init u64 get_kaslr_seed(void *fdt)
> return ret;
> }
>
> -static __init bool cmdline_contains_nokaslr(const u8 *cmdline)
> -{
> - const u8 *str;
> -
> - str = strstr(cmdline, "nokaslr");
> - return str == cmdline || (str > cmdline && *(str - 1) == ' ');
> -}
> -
> -static __init bool is_kaslr_disabled_cmdline(void *fdt)
> -{
> - if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
> - int node;
> - const u8 *prop;
> -
> - node = fdt_path_offset(fdt, "/chosen");
> - if (node < 0)
> - goto out;
> -
> - prop = fdt_getprop(fdt, node, "bootargs", NULL);
> - if (!prop)
> - goto out;
> -
> - if (cmdline_contains_nokaslr(prop))
> - return true;
> -
> - if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
> - goto out;
> -
> - return false;
> - }
> -out:
> - return cmdline_contains_nokaslr(CONFIG_CMDLINE);
> -}
> +u64 kaslr_feature_val __initdata;
> +u64 kaslr_feature_mask __initdata;
>
> /*
> * This routine will be executed with the kernel mapped at its default virtual
> @@ -126,7 +95,7 @@ u64 __init kaslr_early_init(void)
> * Check if 'nokaslr' appears on the command line, and
> * return 0 if that is the case.
> */
> - if (is_kaslr_disabled_cmdline(fdt)) {
> + if (kaslr_feature_val & kaslr_feature_mask & 0xf) {

nit: Isn't the 0xf redundant here? You don't re-mask for VH either.

> kaslr_status = KASLR_DISABLED_CMDLINE;
> return 0;
> }
> --
> 2.29.2
>